BSL PRO Lesson H25-H26 - BIOPAC

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05.11.2021

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BSL PRO Lesson H25-H26: BSL PRO Signal Processing Breadboard Labs

Signal Processing Breadboard Lab Summary:

Lab 1: Square Wave Oscillator Lab 5: Notch Filter for 50/60 Hz Rejection video 2

Lab 2: Instrumentation Amplifier video 1 Lab 6: QRS Detection: Band Pass Filter video 3

Lab 3: High Pass Active Filter Lab 7: QRS Detection: Absolute Value Circuit video 4

Lab 4: Active Gain Block and Low Pass Filter

Lab 8: QRS Detection: Low Pass Filter and Overall System Test Video 5-log

The Signal Processing Labs use the BIOPAC SS39L/SS39LA Signal Processing Breadboard, the SS39L/SS39LA Interface Cable, SS60L/SS60LA Interface Cable, and the BSLTCI-22 Breadboard Electrode Interface.

NOTE: In BSL 4.1.2 and higher, this Lesson Procedure PDF is also embedded in the graph template’s Journal but is best viewed with the Journal set to “Floating display.” See Appendix for details.

http://www.biopac.com/

https://www.biopac.com/video/?video_category=biopac-student-lab&v=bsl-bme-notch-filter

https://www.biopac.com/video/?video_category=biopac-student-lab&v=bsl-bme-instrumentation-amplifier

https://www.biopac.com/video/?video_category=biopac-student-lab&v=bsl-bme-band-pass-filter

https://www.biopac.com/video/?video_category=biopac-student-lab&v=bsl-bme-absolute-value-circuit

https://www.biopac.com/video/?video_category=biopac-student-lab&v=bsl-bme-qrs-detection

BSL PRO Lesson H25-H26 BIOPAC Systems, Inc.


Signal Processing Background

The human body can be studied by viewing the potential difference (Voltage) between strategically placed surface electrodes. Because surface electrodes are an easy, non-invasive way to obtain information about the body, they represent a good starting point for examining the types of electronic circuits used in Biomedical Engineering.

In order to view and record the potential difference between surface electrodes, electronic circuits are used. Electrode leads, which are essentially wires, connect the electrodes to the circuit. Most signals from physiological activity have small amplitudes and must be amplified and processed before they can be viewed in a meaningful way. The good news is that the characteristics of biopotential amplifiers are much the same as any other amplifier. We will review the basics of amplifiers, with special emphasis on the biopotentials.

1. Gain. Physiological signals have amplitudes that range from several microvolts to a few millivolts. To drive display and recording equipment, most biopotential amplifiers have gains of 500 or greater. It is useful to use the decibel form of gain, which is obtained from linear form by the formula:

( )log20)( 10 GainLineardBGain =

2. Common-mode rejection (CMR). The human body makes a reasonably good antenna, and will create electric potentials from electromagnetic radiation present in the atmosphere. A serious problem is 50/60 Hz radiation - present almost anywhere there is electric power. The problem become acute when the biopotentials we wish to monitor have useful energy in the 50/60 Hz range. CMR is the property of canceling any signals that are in common to both inputs, while amplifying differential signals (a potential difference between the inputs). Both AC and DC CMR are important for physiological signals. CMR is usually specified for a common-mode voltage change at a certain frequency. The common-mode rejection ratio (CMRR) is first obtained:

)(OUT

CM

D VV

ACMRR =

where DA is the differential gain of the amplifier

CMV is the common-mode voltage present at both inputs of the amplifier

OUTV is the output voltage result when the common-mode inputs are applied

The logarithmic conversion of CMRR, common-mode rejection is defined as:

( )log20)( 10 CMRRdBCMR =

3. Frequency response. The bandwidth of a physiological amplifier should accurately amplify all the frequencies of importance in the signal, while rejecting those signals outside the bandwidth of interest. The bandwidth is defined as the difference between the low frequency cutoff and high frequency cutoff. The cutoff is defined at the point where the gain is 0.707 of the midpoint gain of the response, and is alternatively called the half power point

( )5.0707.0 2 = , or –3dB point, since ( )707.0log20)(01.3 10=− dB .

4. Input impedance. A fundamental rule of measurement is to not allow the measuring device to influence the signal under observation. An amplifier should exhibit high input impedance so as to not measurably attenuate physiological signals being measured. In the case of the ECG, the ECG electrode itself has low impedance, but skin impedance can range from 100 ohms to 1M ohm. Amplifier input currents cause potentials across the skin impedance that are amplified by the gain of the amplifier, causing large DC offsets in the amplifier output.




5. Noise and drift. Unwanted signals that contaminate physiological measurements, noise produced within amplifier circuitry is generally defined as those signals with components above 0.1Hz, while drift refers to the changes in

baseline below 0.1Hz. Noise can be measured in microvolts peak to peak ( ppV − ) or microvolts root mean

square ( RMSV ). Sources of drift include offset voltage drift (varying input impedance), and gain drift, usually

affected most by temperature.

6. Electrode polarization. Electrodes made of metal, and used with a electrolyte, such as the standard ECG Silver/Silver chloride electrode, form small potentials resulting from ion electron exchange between the electrode and the electrolyte (as in a battery). The challenge for the amplifier designer is to amplify the weak physiological signals in the presence of these polarized dc signals.

ECG Background

The generation of electrical activity in the heart is characterized by mechanical events. During the period of diastole, the heart rests between beats, and assumes its maximum size while filling with blood that has been oxygenated by the lungs and venous blood from the body. Mechanical activity in the heart is called systole and is initiated by contraction of muscles surrounding the atria by electrical stimulation. The stimulations of the sinoatrial node (SA node), a bundle of nerves located in the right atrium, start the heartbeat and set the frequency of cardiac rhythm. This rhythm can be modified by nerve fibers external to the heart that function to control the hearts response to increases or decreases in the body’s demand for blood. Contractions of muscles comprising the atria are stimulated by impulses generated by the SA node.

Impulses from the SA node are conducted along nerve fibers in the atrium to depolarize the atriovetricular node (AV node). AV node stimulation causes contraction of the muscles comprising the ventricles via the bundle of His and the Purkinje conducting system. The depolarization and repolarization of the SA node is followed by the depolarization and repolarization of the AV node – this is the electrical control system that initiates the muscle contractions necessary to maintain the heart’s pumping action. This nerve system generates the external action potentials known as electriocardiogram (ECG), which can be recorded by electrodes at the surface of the body.

ECG waveform and heart function (from Biophysical Measurements, P. Strong, Tektronix Inc.)

It is important to understand the basic functions of the heart as shown by the ECG waveform. The QRS spike is associated with the rapid depolarization of ventricular muscle immediately preceding its contraction. The P wave is the result of atrial depolarization and the T wave is caused by ventricular muscle repolarization.

Monitoring this electrical generator, enclosed in a torso, is the function of electrocardiography. By attaching electrodes to certain places on the body, the small electrical potentials on the surface are sensed. The potentials can then be amplified, conditioned and displayed to give a representation of the heart’s electrical activity. Assuming we will be using the basic frontal plane cardiac vector—a standard placement of electrodes—we can construct a simple ECG monitor to record the potentials.

Circuit requirements:

The ECG QRS spike can range from 400 uV to 2.5 mV peak, and will require a voltage gain of 100 to 1000. ECG bandwidth has been standardized to make interpretation of the results uniform. Two filters with 3 dB cutoffs are used – a high pass filter at 0.05 Hz and a low pass filter at 100 Hz. A 60 Hz (or 50 Hz) notch filter is used to attenuate nominal mains interference.




Although the waveform of the ECG is considered as a low frequency AC signal, there can be significant DC offsets between the electrodes on the body (0 to ±20 mV DC). With a voltage gain at +1000, a DC offset of 20 mV will cause an amplifier to try to produce a signal at 20.0 V, higher than typical power supplies permit. We must prevent DC offsets from swamping the AC signal of interest, and we do this with a high pass filter.

Signals present on the electrodes higher than 100 Hz contribute noise to the ECG that must be reduced to present an accurate view of the ECG. Potentials generated from muscle activity are undesirable in the ECG and are partially reduced with the low pass filter (it is required that a person being monitored for ECG remain relaxed and motionless.)

There are numerous other potentials that are inadvertently amplified when using electrodes to monitor ECG. The mains power produces very high levels of EMI interference, which must be carefully eliminated. The use of shielded electrodes, coupled into a differential amplifier, can reduce EMI mains interference dramatically. Other sources of EMI include radio stations, cell or portable phones, microwave sources, computers, and automotive ignition. We will not attempt to squelch all these sources of interference, although you may experience them in your circuits.

Breadboard Setup

The SS39L/LA Breadboard is designed to rapidly prototype the ECG circuitry without the use of soldering equipment.

Close examination of the SS39L/LA Breadboard reveals that there are five individual boards mounted on the plastic base. The top bus strip has a row of two power bus rows. Next is a strip that contains a 5x64x2 connection array, designed to easily accept 0.3” Dual In Line (DIP) integrated circuits (IC). Beneath the 5x64x2 strip is another power bus strip identical to the top strip. The BIOPAC lessons do not use or refer to the bottom two boards.

The power busses are not labeled on the SS39L/LA, so for safety and reliability, add the following labels:

• Top Row: ‘-5’

• Row above row A: ’G1’

• Row below row J: ‘G2’

• Next Row: ‘+5’

The power strips must be wired so that the top bus is connected to -5.0 V (Green terminal), the bus above row A is GND (Black terminal), the bus below row J is also GND (Black terminal), and the last bus is connected to +5.0 V (Red terminal).

Needle nosed pliers are recommended for inserting wires into the breadboard.

1. Connect a Brown 1.0” jumper from the Black terminal (GND) to the bus above Row A (G1). Connect a Red 2.0” jumper from G1 to G2.

2. Connect a Yellow 4.0” jumper from the Red terminal (+5 V) to the bus +5.

3. Connect a Brown 1.0” jumper from the Green terminal (-5 V) to the bus -5.

4. Each bus is actually divided into two half busses. Bridge all the busses by adding four 0.3” Orange jumpers as shown below.

Next, place all the integrated circuits and wire them to the power busses, adding the decoupling capacitors.




1. Place the LMC6484A with pin 1 in row F, column 55

2. Place an LM324 with pin 1 in row F, column 35



5. Connect four 0.01 uF capacitors with one end in pin 4 of each IC, the other end to G2 bus.

6. Connect four 0.01 uF capacitors with one end in pin 11 of each IC, the other end to G1 bus.

7. Check all capacitors for short circuits.

8. Place the BSLTCI-22 Breadboard Electrode Adapter with pin 1 in row A, column 48.

Power Verification

BME ECG Board Layout with Integrated Circuits

The following steps will apply +5 V and -5 V isolated power to the breadboard from the MP36/MP35/MP46/MP45. The MP36/MP35/MP46/MP45 power is limited to about 100 ma. If the MP36/MP35/MP46/MP45 power is overloaded by the breadboard circuitry due to improper wiring, the MP36/35 may not perform acquisitions properly.

1. If inserted, remove the DB9 end of the SS39L/LA cable from the MP36/MP35/MP46/MP45, and turn off the MP36/MP35. (Disconnect MP46/MP45, as it has no power button.)

2. Plug in the SS39L/LA Cable Black (GND) banana plug into the Black terminal jack.

3. Plug in the SS39L/LA Cable Red (+5) banana plug into the Red terminal jack.

4. Plug in the SS39L/LA Cable Green (-5) banana plug into the Green terminal jack.

5. Plug in the SS39L/LA Cable GND Reference pin into the breadboard GND bus G1.

6. Plug in the SS39L/LA Cable SIGNAL pin into the breadboard GND bus G1.

7. Plug in the SS39L/LA Cable DB9 plug into CH1 of the MP36/MP35/MP46/MP45.

8. Plug in the SS60L/LA Cable DB9 plug into CH2 of the MP36/MP35/MP46/MP45.

9. Plug in the SS60L/LA Cable SIGNAL pin into the breadboard GND bus G1.




10. Plug in the SS60L/LA Cable GND pin into the breadboard GND bus G1.

11. Turn on power to the MP36/35/45. Verify 5 V(±5%) and -5 V(±5%) power buses with a DVM.

• If at any time during the experiments the measured power busses drop below their rated values, turn off the MP36/35/45 and find the cause of the circuit overload in your breadboard wiring.

12. Start BSL PRO. Make a sample reading of the MP36/MP35/MP46/MP45 (Start). Verify that the reading is ~0.00 V DC. If there is a problem with power that causes the MP36/MP35/MP46/MP45 startup routine to fail, the Busy light on the MP36/MP35/MP46/MP45 front panel will flash an error code sequence, and will not allow a recording to occur. The Busy light normally comes on for 1 or 2 seconds, blinks once for USB renumeration, stays on for 10-20 seconds for self-calibration, then turns off. The Busy light then monitors USB data transfers.




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Page 9 of 60 Lab 1

Lab 1: Square Wave Oscillator

Objectives:

1. Create a Square Wave Oscillator, which will be used to test the remaining circuits in the BME labs.

2. Approximate the magnitude of an ECG signal.

Background:

The step voltage has great value in analysis of amplifiers. The square wave generator built in this lab is used later to determine gain and AC-response of the remainder of the circuits in the BME Breadboard Labs. Square wave generators are available commercially, but self-test is an important part of most modern medical equipment, so it is included as the first project.

A Square Wave Oscillator can be designed using the opamp as a Schmitt comparator, using a single quad opamp (Fig. 1.1).

Fig. 1.1 Schematic for SS39L/LA Breadboard Lab 1

Referring to the schematic, the Square Wave output voltage is Vo, and the voltage across the capacitor is Vc. The voltage across the comparator inputs Vi is the difference of (Vc – ßVo). Assuming an ideal comparator response, with the voltage Vi < 0, the capacitor charges exponentially toward Vo through the RC combination. The output stays at Vo until Vc=+ßVo, which causes the comparator output to reverse to –Vo. Vc charges exponentially toward –Vo. The output will continue this cycle, with the period T:

( )21ln22

1

13 RR

CRT +=

The output will swing rail to rail. With the LMC6484 opamp (supplied with the SS39L/LA), expect ~9.8 Vpp signal out, with some offset due to mismatch between positive and negative rail levels. This will also affect the square wave symmetry.

The oscillator is followed by an amplifier which provides a divide by 19.6 (0.5 Vpp) which, in turn, is followed by another amplifier that divides by 200 (2.5 mVpp). The 2.5 mVpp square wave is a signal level very close to the expected ECG signal, and can be used to test the instrumentation amp gain, as well as the high and Low Pass filters. The 0.5 Vpp will be used for the common mode test of the instrumentation amp.


Page 10 of 60 Lab 1

Laboratory:

Hardware Setup

1. Build the square wave oscillator and divisor functions per the Lab 1 Schematic (Fig. 1.1).

2. Connect the interface cables to the MP36/MP35/MP46/MP45 unit.

a. SS39L/LA into CH1 on the MP36/MP35/MP46/MP45

b. SS60L/LA into CH2 on the MP36/MP35/MP46/MP45

3. Connect the interface cables to the breadboard to monitor the square wave outputs.

a. MP36/MP35/MP46/MP45 CH1 signal input to 0.5 Vpp (IC1 pin 7).

b. MP36/MP35/MP46/MP45 CH2 signal input to 2.5 mVpp (IC1 pin 8).

c. Connect the negative leads to the ground bus.

Software Setup

Set the BSL PRO software for recording as follows:

▪ Use the pre-configured SqWvGen.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- SqWvGen Template” from the lesson list and click OK.

The h25-h26 directory may also be accessed from within the BSL PRO application via “File > Open.”

The steps below are for Manual Graph Setup and not necessary if the pre-configured graph SqWvGen.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 11.)

1. MP36/MP35/MP46/MP45 > Set Up Data Acquisition > Channels:

a. Enable Acquire, Plot, and Value for CH1 and CH2, and enter the following label for each channel.

b. Click “Setup…” for CH1 and set parameters as follows:

i) Filters 1, 2, 3: None; Gain: x50, Offset: 0; Input coupling: DC

ii) Scaling 10 mV → 50 mV and -10 mV →-50 mV. Scaling is set at x5 to account for the probe’s ÷5 internal resistor scaling.|


Page 11 of 60 Lab 1

c. Click “Setup…” for CH2 and set parameters as follows:

i) Filter 1,2,&3: None; Gain: x2000; Offset: 0; Input coupling: DC

ii) Scaling 10000 microV (or 10 mV) → 50 mV and -10000 microV (or 10 mV) → -50 mV. Scaling is set at x5 to account for the probe’s ÷5 internal resistor scaling.

d. Click OK as required to exit Set up Channels.

2. MP36/MP35/MP46/MP45 > Set Up Data Acquisition > Length/Rate

a. Mode: Record, Save Once, PC Memory

b. Sample Rate: 5000

c. Acquisition Length: 5 seconds (minimum)

3. Use two measurement rows. To set up, select (Display > Preferences > Measurements). Show 2 measurement rows and 5 measurement columns. Show 3 digits of precision.

Recording

1. Press the “Start” button in the software window to begin recording.

2. After at least 5 seconds, press the “Stop” button.


Page 12 of 60 Lab 1

Analysis

1. Set the following measurements for each channel:

a. Freq (frequency) d) Stddev (standard deviation)

b. Mean e) P-P (peak-to-peak)

c. Delta T (time)

2. Select a section of the high output level for each channel, avoiding any ringing at the transitions, and measure Mean.

3. Select a section of the low output level for each channel, avoiding any ringing at the transitions, and measure Mean.

4. Select one square wave cycle and measure Freq, Delta T, and Stddev, P-P for each channel.

▪ Standard deviation of a square wave is ½ the P-P value. Standard deviation is equal to RMS, but with the added bonus of DC removal.

5. Do you notice “noise” on the 2.5 mVpp signal? Magnify a section of the signal to measure the frequency and amplitude.


Page 13 of 60 Lab 1

Data Report for Lab 1:

1. Report all findings of the Lab.

Channel High Mean Low Mean Freq Delta T Stddev P-P

CH1

CH2

2. Include recorded graphs of the results.

▪ To paste graphs into an open Word document, select Edit > Clipboard > Copy Graph in BSL PRO and then right-click in the Word document and select paste.

3. Review the findings.

a. Is the square wave symmetrical (are the periods for both halves of the cycle equal)?

Yes No

b. What is the ratio of the noise to the 2.5 mVpp signal?

c. Report any discrepancies from actual results and expected results.

▪ Expected results: Frequency: 1.0 Hz ±20%; Output Voltage at voltage dividers: 0.5 Vpp and 2.5 mVpp ±10%

d. Report suspected causes for any discrepancies.

e. How was /could the problem(s) be fixed?

4. What is the correlation between the Delta T and Freq measurements? (answer as an equation)

5. Why is the Stddev measurement more precise than the P-P measurement?

End Lab 1


Page 14 of 60 Lab 2

Lab 2: Instrumentation Amplifier


Objectives

1. To build a simple instrumentation amp to act as a primary interface for medical transducers, such as electrodes or bridge resistance sensors.

2. To use the Square Wave 2.5 mVpp signal as a single ended input to test for Gain.

Background:

An instrumentation amplifier (InAmp) is a device that amplifies the difference between two input potentials, while rejecting any signals that are common to both inputs. The InAmp is usually assigned the delicate job of extracting small signals from sensors and transducers, in instruments such as ECG, EEG, blood pressure monitors and defibrillators. They are especially effective in removing both common mode DC and low frequency AC signals, essential for monitoring human body potentials. The most important property of InAmps is common-mode rejection (CMR), the property of canceling out any signals that are common to both inputs, while amplifying any signals that provide a potential difference to the inputs.

Instrumentation amps have several features in common:

A. Balanced, differential inputs each with high impedance and low bias currents

B. Single ended output with respect to a reference terminal

C. A closed loop gain block with gain setting resistor isolated from the signal terminals

D. Low output impedance, normally several milliohms at low frequencies

Why not use an opamp—don’t opamps have balanced differential inputs with high impedance, low output impedance, and a gain block? Because, in the typical inverting or non-inverting circuits, both the signal and the common mode voltage appear at the amplifier output. The opamp does exhibit CMR, but the signal is amplified by the opamp’s closed-loop gain, while the common mode voltage receives unity gain, reducing the opamps’s output swing. To summarize the problems of just using an opamp, inadequate DC CMR will produce undesirable offsets at the output. Inadequate AC CMR causes large, time-varying errors that change with frequency, making the errors difficult to remove in following electronic circuits.

Another important property of InAmps is low noise voltage and current. Input noise is Referred To Input (RTI), so that a

specification of 10 nV/ Hz @1 kHz will be multiplied by the differential gain at the output. If the InAmp is operated at high

gain, then the InAmp input noise can become the largest noise source of the entire circuit.

An InAmp must provide adequate bandwidth for an application. Unity bandwidths of up to 4 mHz are typical of good InAmps. Most InAmps specify bandwidths at several gain settings, to show how the bandwidth decreases with increased gain.

AC CMR varies with frequency and gain. For most InAmps, the CMR increases with gain (up to a certain point) because most designs have a front end configuration that rejects common-mode signals while amplifying differential voltages. Since any imbalance in the differential input will show up as a common-mode error, AC CMR decreases with frequency.

In this lab, an InAmp for an ECG application (Fig. 2.1) is built.


Page 15 of 60 Lab 2

When setting the gain, use what is known about the required measurement(s) to obtain the largest gain possible from the InAmp without exceeding its capabilities. It is important to design the best CMR from the front end, because the sensors are really only electrical conductors attached to the body (antennas). The electrodes will pick up every imaginable form of electromagnetic energy present, from the heart, muscles, nearby heterodyne radios, computers, AC mains, electric lights, radio stations, transmissions from friendly aliens, microwave ovens and waffle irons. Even the best attachment of electrodes to the body cannot fully account for skin resistance, which is surprisingly high and varies from electrode to electrode.

Although input voltage offset will be multiplied by the gain of the circuit to contribute to DC offset at the output, the dominant output DC offset will be from DC potentials between the electrodes. In this lab, expect as much as 25 mV between the two signal electrodes. The LM324 data sheet (available at: http://www.ti.com/lit/ds/symlink/lm124-n.pdf shows the output voltage swing from the LM324’s opamps is about 1.2 V from the supply rails. The MP36/MP35/MP46/MP45 Channel input jacks will provide ±5 V supplies, so that allows ±3.8 V swings. The ECG signal is not expected to exceed 2.5 mV, although the common-mode signals may be 100 times higher, or more. The front end of the InAmp must accurately reproduce the common-mode signals so that they can be cancelled out by the following difference amplifier. To calculate the maximum voltage swing that will not exceed the output swing limitation (3.8 V in this lab):

Max voltage swing = DC electrode offset + ECG signal + CM noise + Input Offset

For this lab:

Max voltage swing = 25 mV +2.5 mV + 1.0 mV + 3 mV = 31.5 mV

Although a maximum gain of (3.8 V/32.5 mV) = 117 is possible, a more conservative gain of 101 is recommended.

The bandwidth of the ECG is very small (100 Hz), so bandwidth is not a major concern, even at very high gains. The input offset of 4.0 mV may contribute to DC offsets at the output.

Laboratory:

Hardware Setup for Gain Measurement

1. Build the square wave oscillator and divisor functions per the Lab 2 Schematic (Fig. 2.1). Matching the 4 resistors of the difference amp section can improve CMR. Carefully measure R10, R11, R12 and R13 with a high quality DVM, noting the values of each resistor. Make the ratio of R13/R12 as close as possible to R11/R10.

▪ Leave at least 8 vertical busses vacant on the end of the LM324 for test hookup, as well as placement of the Electrode breadboard adapter





a. MP36/MP35/MP46/MP45 CH1 signal input to U2 pin 5, +INAMP.

b. MP36/MP35/MP46/MP45 CH2 signal input to U2 pin 1, INA_OUT.

c. Connect both the signal grounds/negative leads to the ground bus.

http://www.ti.com/lit/ds/symlink/lm124-n.pdf


Page 16 of 60 Lab 2

4. Connect the square wave generator (Lab 1) to the InAmp inputs to use the Square Wave 2.5 mVpp signal in a single ended configuration to test for Gain.

a. Square Wave Generator 2.5 mVpp output (U1 pin 8) to +INAMP input (U2 pin 5).

b. Connect -INAMP (U2 pin 10) to the ground bus G1.

Software Setup for Gain Measurement

Set the BSL PRO software for Gain Measurement recording as follows:

▪ Use the pre-configured InAmpGain.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- InAmpGain Template” from the lesson list and click OK.


The steps below are for Manual Graph Setup and not necessary if the pre-configured graph InAmpGain.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 18.

1. MP36/MP35/MP46/MP45 > Set up Channels:

a. Enable Acquire, Plot, and Value for CH1 and CH2, and enter the following label for each channel.

b. Click the “Setup” for CH1 and set parameters as follows:

i. Filters 1, 2, 3: None; Gain: x200, Offset: 0; Input coupling: DC


Page 17 of 60 Lab 2

ii. Click “Scaling” and set to: 10 mV → 50 mV and -10 mV →-50 mV

c. Click “Setup” for CH2 and set parameters as follows:

i. Filter 1,2,&3: None; Gain: x50; Offset: 0; Input coupling: DC

ii. Click “Scaling” and set to: 10 mV → 50 mV and -10 mV → -50 mV


2. MP36/MP35/MP46/MP45 > Set up Acquisition

e. Mode: Record, Save once, Memory

f. Sample Rate: 5000

g. Acquisition Length: 5 seconds (minimum)

3. Use two measurement rows. To set up, select (File > Preference > General). Show 5 measurement columns. Show 3 digits of precision.


Page 18 of 60 Lab 2

Recording for Gain Measurement

1. Segment 1: Gain

a. Press the “Start” button in the software window to begin recording.

b. Wait for the recording to stop after 5 seconds, or press the “Stop” button.

c. Set the measurement rows to read Stddev, P-P and Mean for each channel.

2. Using the I-beam selection tool, select one full cycle of the square wave. 3. Measure the Stddev for the input and output signal.

a. Measure the CD offset of the output – the mean of exactly one cycle b. Verify the gain is 101 ±2%. c. Paste the recorded graph into an open Word document for your report.

▪ To paste graphs into an open Word document, select Edit > Clipboard > Copy Graph in BSL PRO and then right-click in the Word document and select paste. Use Edit > Clipboard > Copy Measurement to copy measurement data.

d. Note the measurements notes results in a table:

Stddev P-P Mean

Channel 1

Channel 2

e. Note any anomalies. Do any square waves droop? Is there phase inversion between channels?

Hardware Setup for CMRR Measurement

1. When we measured the gain, we injected a low level signal into the positive +InAmp input, while holding the –InAmp input at GND. We demonstrated that the InAmp is working properly when we recorded an output with the correct gain. To test CMRR, we will inject a high level signal into both inputs on the InAmp, and then measure the output. Ideally, with infinite CMR, the output would remain at 0.0 V DC. We need a high level input, because the InAmp is very good at suppressing signals that appear on both inputs, and we need to be able to see the output with reasonable accuracy.

2. Connect MP36/MP35/MP46/MP45 CH1 signal input to U2 pin 5, +INAMP. Connect the Ground wire to GND.

3. Connect MP36/MP35/MP46/MP45 CH2 signal input to U2 pin 1, INA_OUT. Connect CH2 Ground wire to GND.

4. We will now change the input from the 2.5 mVpp signal to the 0.5 mVpp signal. This will require moving one end of a jumper that was inserted in the Hardware Setup for Gain measurement at the beginning of the experiment. Lift the end of the jumper from U1-pin 8 (2.5 mVpp) and insert it into U1-pin 7 (0.5 Vpp). The other end of the jumper should remain in U2-pin 5 (+IN_AMP).


Page 19 of 60 Lab 2

5. Remove the jumper from U2-pin 10 to GND. Connect a jumper from U2-pin5 to U2-pin 10. This will insert the same 0.5 Vpp signal into both InAmp inputs.

Software Setup for CMRR Measurement

Set the BSL PRO software for CMRR Measurement recording as follows:

▪ Open a New Window for recording. (File > New Graph Window) or use the InAmpCM.gtl template (File > Open > InAmpCM.gtl) to simplify setup.

▪ OR: From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- InAmpCM Template” from the lesson list and click OK.

The steps below are for Manual Graph Setup and not necessary if the pre-configured graph InAmpCM.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 20.

1. Configure the Channel Set Up Parameters as follows:

a. Enable Acquire, Plot and Value for CH1 and CH2. Channel Labels: CH1; 0.5 V CM input, CH 2; InAmp CM out.

b. Click “Setup” for CH1 and set parameters as follows:

i. Filter 1, 2, & 3: None; Gain: x50; Offset: 0; Input coupling: DC

ii. Click “Scaling” and set to: 10 mV → 50 mV, -10 mV → -50 mV


Page 20 of 60 Lab 2


i. Filter 1, 2 & 3: None; CH2: Gain = x200 (or x100 if DC offsets are too high); Input coupling: DC

ii. Click “Scaling” and set to: 10 mV → 50 mV, -10 mV → -50 mV


2. MP36/MP35/MP46/MP45 > Set Up Data Acquisition > Length/Rate.

a. Mode: Record, Save once, Memory


c. Acquisition Length: 5 seconds (minimum)


Recording for CMRR Measurement

1. Record 5 seconds of data. Using the selection tool, select one cycle of the square wave. Use the measurement tool to read the Stddev for both channels.

2. Paste the recording into an open Word document (your lab write-up).

3. Record the Stddev for the CH1 CM input, and CH2 InAmp Output CM.


Page 21 of 60 Lab 2

Analysis and Data Report for Lab 2:

1. Report all results of the Lab. Include recorded graphs of the results.

▪ To paste graphs into an open Word document, select Edit > Clipboard > Copy Graph in BSL PRO and then right-click in the Word document and select paste.

2. Gain measurements:

a. how the recordings for the gain measurement. Verify the operation, and show the gain calculation.

b. Note the square wave levels and their offset.

c. Do any square waves droop?

d. Note any phase inversion between channels.

e. Calculate the Gain and compare to the expected gain of 101.

3. CMRR Measurements

a. Show the recordings for the CMRR calculation including the measurement settings. Show the CMRR calculation, and the DC offset.

b. CMRR calculation:

Differential Gain=101

Common mode gain= Output StdDev/Input Common Mode StdDev

CMRR=Differential gain/Common mode gain

c. Calculate Common Mode Rejection CMRRdBCMR log20)( =

d. Report any discrepancies from actual results and expected results.

Expected results: CMR -40 dB to -120 dB

e. Report suspected causes for any discrepancies.

f. How was/could the problems(s) be fixed?

End Lab 2


Page 22 of 60 Lab 3

Lab 3: High Pass Filter


Objective:

1. To design, build and test a High Pass active filter to demonstrate the bio-medical application of filters in an ECG monitor.

Background:

Wilhelm Einthoven is credited with designing the first ECG using a magnetic string galvanometer. Since then, recording of ECG signals has been standardized to accurately interpret the results. The standard requires two filters: a High Pass filter with a -3 dB cutoff at 0.05 Hz and a Low Pass filter -3 dB filter cutoff at 100 Hz. The High Pass filter specified here is a standard second order Butterworth filter (Q=0.707)—preferred for its maximally flat response and reasonably good roll-off. Other filter topologies offer steeper roll-offs, but typically have ripple in the pass band and increasing non-linear phase. For ECG filters, avoiding excessive non-linear phase is important because non-linear phase will result in varying group delay within the ECG frequency band. This effect is problematic because varying delays at different frequencies will result in distortion of the ECG signal, thus confusing diagnosis of possible physiological problems.

The main purpose of the High Pass filter in ECG monitoring applications is the removal of DC offsets from the ECG signal that are present after the initial amplification stage. DC removal is necessary to move the signal as close as possible to the middle of the power supply rails, so that the following circuitry can filter, and further amplify if necessary. That is why the High Pass filter precedes the Low Pass filter.

The 0.05 Hz High Pass filter used here has the advantage of having a pass band that extends well below 1 Hz, and the final ECG waveform will display a minimum of filter induced sag. A disadvantage of this filter is its very long settling time, which can cause long waiting periods until signals can be properly displayed. Another problem is the large capacitors that are required. A 1 Hz High Pass filter might be implemented because of these practical issues of construction and observation. A 1 Hz filter is far more useful for monitoring the ECG under conditions of body motion to permit physiological monitoring during the course of exercise. Normally, during exercise, electrodes on the body shift position, thus causing artifacts at the low end of the ECG spectrum. A 1 Hz High Pass filter helps reduce this effect.

The Sallen-Key configuration shown in the BME Laboratory ECG Amplifier schematic is a biquad implementation, meaning there are two poles in the circuit transfer function:

When C6=C7=C, the form becomes:

2

00

2

2

/ ++=

Qss

s

Vi

Vo

where RR =14 RQR )4( 2

15 = and Q

CR02

1

=


Page 23 of 60 Lab 3

Laboratory:

Hardware Setup

1. Build the active High Pass filter per the Lab 3 Schematic (Fig. 3.1). C=10uF R14=226K R15=453K

2. To further develop the ECG amplifier, connect (as in Fig. 3.1):

a. High pass input to instrumentation amp output

b. Square wave generator 2.5 mV P-P output (U1 pin 8) to +INAMP (U2 pin 5)

c. –INAMP (U2 pin 10) to GND





a. MP36/MP35/MP46/MP45 CH1 signal input to INA_OUT (IC2 pin 1).

b. MP36/MP35/MP46/MP45 CH2 signal input to HPF_OUT (IC2 pin 14).


Software Setup


Use the pre-configured High Pass.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- High Pass Template” from the lesson list and click OK.

▪ The h25-h26 directory may also be accessed from within the BSL PRO application via “File > Open.”

The steps below are for Manual Graph Setup and not necessary if the pre-configured graph High Pass.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 25.

1. MP36/MP35/MP46/MP45 > Set up Channels:

a. Enable Acquire, Plot, and Value for CH1 and CH2, and type the following labels for each channel.


Page 24 of 60 Lab 3



ii. Click “Scaling” and set to 10 mV → 50 mV and -10 mV →-50 mV


i. Filter 1, 2, 3: None; Gain: x100; Offset: 0; Input coupling: DC




a. Mode: Record, Save once, Memory


c. Acquisition Length: 300 seconds.



Page 25 of 60 Lab 3

Recording

Press the “Start” button in the software window to begin recording. The High Pass output may drift, but should be centered at 0.00V within 30 seconds. Then press “Stop”.

High Pass filter function with a complete cycle highlighted.

Hardware Setup for Electrode Interface

1. To view actual ECG waveforms, we will now remove the 2.5 mVpp test signal and connect the SS2L Electrode Assembly, using the BSLTCI-22 Breadboard Electrode Interface.

2. Remove jumper from 2.5 mVpp (U1 pin 8) to +InAmp (U2 pin 5)

3. Remove jumper from –InAmp (U2 pin 10) to GND.

4. Connect TCI-22 pin 2 to +InAmp U2 pin 5.

5. Connect TCI-22 pin 4 to –InAmp U2 pin 10.

6. Connect TCI-22 pin 3 to GND bus.

7. Attach electrodes to a human subject for an ECG recording.

It is a good idea to lightly abrade the skin (using an ELPAD), before electrode placement to decrease the impedance between the electrode and the skin surface.

Establish a standard Lead II configuration with three EL503 disposable electrodes: Attach the GND (BLACK) electrode on the right leg, the POS (RED) electrode to the left leg and the NEG (WHITE) electrode to right forearm.


Page 26 of 60 Lab 3

SS2L inserted into BSLTCI-22 Breadboard Electrode Interface, connected to input of InAmp.

8. Save the current graph (File, SaveAs, “MyHighPass.acq”). Record the ECG wave by clicking “Start” – since we are in Append mode, the data is attached to the end of the current graph window. You may have to wait a long period for the waveforms to settle. Try to keep muscles relaxed during acquisition (why?). Large offsets may cause the InAmp output to go offscale – to rescale, click on the right hand side Vertical Scale and enter larger scale factors. Large offsets can be caused by high skin resistance – prepare the skin under the electrode with a gentle abrasive pad to reduce skin resistance. 50/60 Hz noise can sometimes be reduced by keeping the bulk of the electrode leads as close to the body as possible.

ECG High Pass filter function with electrodes input.


Page 27 of 60 Lab 3

Analysis

1. Determine the AC gain of the circuit.

a. Use the Stddev function over one complete cycle for both input and output.

b. Verify gain is 1 + - 1%.

2. Use the I-beam tool to measure the heart rate recorded using the electrodes. Is there “noise” on the recording? Using the magnifying tool, expand a portion of the noise wave. Use the I-beam tool to measure the frequency.

3. High Pass 3dB cut-off measurements.

a. Measure the 3db cut-off frequency using the sag of the high pass output. - Select a complete cycle of the High Pass Output after the waveform has stabilized. - Set the “Freq” measurement

- Select one cycle, and note the freq = f

b. Select a High Pass filter output area that begins after a low-to-high transition, then sags until the high-to-low transition.

- Select an area that does not include the transitions; a period that will be ~T/2, with T = the period of the cycle.

- Set the Delta measurement

- Measure the droop, Vdelta

c. Obtain V max.

- Select a complete low-to-high High Pass Output transition.

- Set the “Delta” measurement.


Page 28 of 60 Lab 3

4. Estimate high pass filter response. According to Jacob Millman (“Microelectronics, Digital and Analog Circuits and Systems,” McGraw Hill, 1979), the response of a single order high pass filter can be estimated using square wave testing using the formula:

f

V

Vdeltaf hp

2

max=

Note: Millman’s formula is an approximation commonly used to derive the highpass filter breakpoint from the measured “tilt” or “sag” in the filter’s square ware response. The Tilt (P) is equal to (Vdelta/Vmax) and P = Pi*ƒhp/ƒ where Pi = 3.1415926..., ƒhp is Highpass filter breakpoint, and ƒ is the frequency of driving square wave. The BSL PRO calculates Vdelta in a manner that requires this value to be multiplied by an additional factor of 2 to reference it properly to the Vmax measurement for the ultimate determination of P.

This lab implements a second order filter, which through simulation, results in the formula:

f

V

Vdeltaf hp

414.1

max=


1. Show recorded graphs of the input and output responses to the High Pass filter, after the output has stabilized.

2. Show the results of the Square wave recording.

3. Show the results of the ECG recording.

4. Show the calculations for gain, and the High Pass 3 dB cut-off frequency.

5. What is the heartbeat frequency of the ECG? What is the frequency of the noise measured on the ECG wave?

6. 3dB cut-off measurements:

freq = f Vdelta V max

7. Estimated high pass filter response:

End Lab 3


Page 29 of 60 Lab 4

Lab 4: Active Gain Block and Low Pass Filter


Objectives:

1. To construct a simple non-inverting amplifier to increase signal level for the laboratory ECG monitor.

2. To follow the amplifier by a Low Pass filter with 3dB cut-off at 100 Hz, to limit the response of the system to the frequencies of interest.

Background:

The non-inverting amplifier of 5x gain is shown in the BME Laboratory ECG Amplifier schematic as Positive Gain Block. The gain is defined as:

17

161R

R

Vi

Vo+=

The InAmp provides a gain of x101, and the High Pass filter removes any DC offsets, leaving a ~100-500 mV signal primarily centered around ground level. Amplify this signal to a ~500-2500 mV level with the gain block and then remove the DC offset with the High Pass filter. Otherwise, the DC Offset may cause the output of the gain block or the Low Pass filter to easily rail because both of these blocks are DC voltage sensitive.

The main purpose of the Low Pass filter in ECG monitoring applications is to limit the bandwidth to the frequencies of interest in the ECG signal. The original ECG signal is on the order of ~1-5 mV. The Sallen-Key configuration of the unity gain Low Pass Filter (LPF) shown in the BME ECG Amplifier schematic (the LPF that follows the Gain Block) is a biquad implementation, meaning there are two poles in the circuit transfer function:

With RRR == 1918

2

00

2

2

0

/

++=

QssVi

Vo

where CC =10 , CQC )4( 2

11 = and Q

CR02

1

=

Modeling the response of an RC circuit to a step response closely approximates the cutoff frequency.

Where the voltage across the output capacitor is given as:

)1(0RC

t

eViv−

−=


Page 30 of 60 Lab 4

The time for 0v to reach a tenth of its final value is 0.1RC, and the time to reach nine tenths of its final value is 2.3RC. rt

is the difference between these two times, so:

hh

rff

RCt35.0

2

2.22.2 ===

and r

ht

f35.0

=

Laboratory:

Hardware Setup

1. Build the active gain block and LPF per the Lab 4 Schematic (Fig. 4.1), with previous experiment’s HPF_OUT (U2 pin 14) connected to U3 pin 10, the gain block. Be sure that the 2.5 mVpp signal (U1 pin 8) is connected to +InAmp (U2 pin 5). Connect –InAmp (U2 pin 10) GND. Remove the SS2L Electrode if it is connected to the BSLTCI-22 Breadboard Electrode Interface.

Gain Block: R17=24.9K R16=100K

Low Pass Filter: C10=.047uF C11=0.1uF

R18=R19=23.7K




3. Connect the interface cables to the breadboard to monitor the Gain block outputs.

a. MP36/MP35/MP46/MP45 CH1 signal input to HPF_OUT (U3 pin 10).

b. MP36/MP35/MP46/MP45 CH2 signal input to GAIN_OUT (U3 pin 8).



Page 31 of 60 Lab 4

Software Setup


▪ Use the pre-configured GainBlkLP.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- GainBlkLP Template” from the lesson list and click OK.


The steps below are for Manual Graph Setup and not necessary if the pre-configured graph GainBlkLP.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 32.







i. Filter 1,2, 3: None; Gain: x50; Offset: 0; Input coupling: DC




a. Mode: Record, Append, Memory



Page 32 of 60 Lab 4

c. Acquisition Length: 300 seconds


Recording

A. Gain Block

Use the Square Wave (~2.5 mV) output, through the InAmp (x101), and the High Pass Filter (x1).


2. After the output has stabilized around ground potential (at least 30 seconds) press the “Stop” button.

B. Low Pass Filter

Use the same square wave generator input, through the InAmp, High Pass filter and gain block.

1. Change the hardware connections to monitor the Low Pass Filter outputs. Move the CH2 probe from U3 pin 8 to U3 pin 14

2. Press the “Start” button in the software window to append recording.

3. After the output has stabilized around ground potential (at least 30 seconds) press the “Stop” button.

Analysis




c. Delta T (time)

2. Measure the Stddev values of input and output channels in a window containing one full cycle, after the output is stable. Verify a DC gain of 5.

3. Measure the P-P signal.

4. To test the LPF cutoff frequency (100 Hz)

a. select in the CH2 Low Pass Output, a low to high transition waveform.

b. Magnify the time base, so that the single transition is visible across the screen.

c. Use the P-P tool to find the total extent of the transition

d. Measure Delta T on a window that starts at 10% of the P-P, and ends at 90% P-P.


Page 33 of 60 Lab 4


1. Show a graph of the input and output responses to the Gain Block, after the output has stabilized.

2. Show a graph of the input and output responses to the LPF.

3. Show a graph of an expanded low to high Low Pass filter output transition, with the 10%-90% areas highlighted.

4. Compare the calculated High Pass 3 db cutoff frequency to the design value and explain any discrepancies between actual results and expected results.

5. Compare calculated gain to measured input and output (Stddev values) in a window containing at least one full cycle. The output of the Gain Block should be 5x the output of the High Pass Filter.

6. Determine the rise time rt ,defined as the time for the waveform to rise from 10% to 90% its final value.

End Lab 4


Page 34 of 60 Lab 5

Lab 5: Notch Filter for 50/60 Hz Rejection


Objective:

1. To construct a notch filter to remove 50 or 60 Hz noise from the ECG signal.

• This lesson uses a Multiple Feedback Band-Reject Filter.

Background:

The second order Band-Reject filter is shown in the BME Laboratory ECG Amplifier schematic as Notch Filter. The notch filter utilizes a Band Pass filter, followed by a summing amplifier, which subtracts the Band Pass output from the input signal.

The Band Pass filter equation is:

( )2

00

2

0

)/(

2

++=

Qwss

Qs

Vi

Vo

With 1312 CCC == 1=Q and 2120

2120

RR

RRReq

+=

Establish the total gain of the Band Pass section multiplied by the gain of the resistor input voltage divider as

1== vrbptotal AAA

The gain of the resistor divider is

2120

21

RR

RAvr

+=

The equations for the Band Pass section are:

22 2 −=−= QAbp 2

23

4Q

RReq =

Cf

QR

023 =

where eqR is the resistance seen by the Band Pass filter section.

2

23

4Q

RReq =

So

2

1=vrA and eqRRR 22021 ==

To produce a band reject function, add the Band Pass filter output to the original signal through an inverting summing section. The component values for a 60 Hz,Q=1 notch filter are as follows:

With C=C12=C13=0.22uF


Page 35 of 60 Lab 5

R23=24.3K

R20=R21=12.1K

For a 50 Hz, Q=1 notch filter, use values 28.7K for R23 and 13.3K for R20 and R21.

Laboratory:

Hardware Setup

1. Build the Notch Filter per the Lab 5 Schematic (Fig. 5.1), with LPF_OUT connected to the junction of R20 and R21





a. MP36/MP35/MP46/MP45 CH1 signal input to LPF_OUT (IC3 pin 14).

b. MP36/MP35/MP46/MP45 CH2 signal input to ECG_OUT (IC3 pin 1).


Software Setup


▪ Use the pre-configured Notch.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- Notch Template” from the lesson list and click OK.


The steps below are for Manual Graph Setup and not necessary if the pre-configured graph Notch.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 36.




Page 36 of 60 Lab 5









e. Mode: Record, Save Once, Memory

f. Sample Rate: 5000

g. Acquisition Length: 30 seconds


Recording

Use the Square Wave (2.5 mVpp) output, through the Instrumentation Amp (x101), High Pass Filter, Gain Block,


Page 37 of 60 Lab 5

and Low Pass Filter.

1. After the circuit has been running with the square wave input for 30 seconds, press the “Start” button in the software window to begin recording.

2. Record about 5 seconds, press the “Stop” button.

3. Save the recording as “Notch1.acq” (File, Save As) for backup in case of difficulty in analysis.

Notch Filter Analysis




c. Delta T (time)

2. Show notch filter using FFT.

a. Select CH2 Band pass Filter by clicking on the 60 Hz Notch Filter label.

b. Select Transform > Difference and apply the default difference of 1 to the entire waveform.

c. Click the Vertical Autoscale icon to scale the result.

d. Select one half cycle (as shown below) to simulate an impulse response for the FFT function.


Page 38 of 60 Lab 5

3. Magnify the lower frequencies to better display the range around the 60 Hz notch. Scale the FFT waveforms.

a. On the output FFT, click on the Vertical Scale, and in the Vertical Scale dialog box, enter (for example) Scale=20 dbV and Midpoint=40 dbV. On the output FFT click on the Horizontal Scale and in the Horizontal Scale Dialog box, enter Scale = 100 Hz and Start = 0

b. Using the I-beam toll, record the depth of the notch and the bandwidth.

Hardware Setup for Electrode Interface







SS2L inserted into BSLTCI-22 Breadboard Electrode Interface, connected to input of InAmp.


Page 39 of 60 Lab 5

Recording 2—ECG

Test the ECG amplifier with actual ECG signals.

7. Attach electrodes to a human subject for an ECG recording.

a. It is a good idea to lightly abrade the skin (using an ELPAD), before electrode placement to decrease the impedance between the electrode and the skin surface.

b. Establish a standard Lead II configuration with three EL503 disposable electrodes: Attach the GND (BLACK) electrode on the right leg, the POS (RED) electrode to the left leg and the NEG (WHITE) electrode to right forearm.

8. Set the BSL PRO software for recording as follows:

a. Use the pre-configured ECG.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- ECG Template” from the lesson list and click OK.

Or manually open a new window and set just like the Notch Filter above, except label CH2 “ECG OUT”. Press “Start” to begin recording.

• If the ECG (50/60 Hz Notch) is inverted, exchange the POS and NEG electrode connectors on the electrodes.

• If excess 50/60 Hz noise is present, adjust (firmly attach) the electrodes for better contact.

9. Insert an event marker (F9 Windows, Esc Mac) for each condition:

a. Subject touches keyboard

b. Subject rapidly clenches/unclenches fist.

c. Subject move arm.

10. After at least 30 seconds, press the “Stop” button

• It may take up to 30 seconds for the waveform to settle (the 0.05 Hz High Pass filter).


Page 40 of 60 Lab 5



• To paste graphs into an open Word document, select Edit > Clipboard > Copy Graph in BSL PRO and then right-click in the Word document and select paste.

a. Show a graph of the input and output responses to the Notch Filter Block, after the output has stabilized.

b. Show the FFT response of the Notch Filter, and the design and calculated values.

c. Show a graph of the ECG measurements. Indicate ECG levels (note total gain of 505).

d. Explain any discrepancies between actual results and expected results.

2. Record the depth of the notch and the bandwidth and compare to the design values.

3. Can you see the effects of the 100 Hz Low Pass filter in the FFT results?

4. What effect did the Subject touching the mouse or keyboard have on 50/60 Hz interference?

5. What effect did the Subject’s rapid fist clenching/unclenching have on the measurement?

6. What effect did the Subject’s arm movement have on the measurement?

End Lab 5


Page 41 of 60 Lab 6

Lab 6: Band pass Filter for QRS Detect Function


Objective:

1. To construct a Band Pass filter as a building block in a QRS wave detector.

Background:

ECG measurements often require synchronization with other medical/lab equipment. The heart rate is an extremely useful synchronization tool. The typical method of obtaining heart rate is to trigger off the QRS wave, because it is the most prominent part of the ECG waveform. The QRS wave has been studied extensively—analysis of the QRS wave in many subjects has shown a pattern of high energy in the 17 Hz band. To trigger off this energy band, amplify the energy found in the QRS band, and reject other frequencies.

The second order Band Pass filter at 17 Hz is shown in the BME Laboratory ECG Amplifier schematic.

The Band Pass filter equation is:

( )2

00

2

0

)/(

2

++=

Qwss

Qs

Vi

Vo

With 1514 CCC == and 5=Q

22 2 −=−= QAv 2

27

264Q

RR =

Cf

QR

027 =

So, with C=C14=C15=0.47uF

R27=200K

R26=2.00K

0 =106.4 0f = 16.9 Hz


Page 42 of 60 Lab 6

Laboratory:

Hardware Setup

1. Build the Band pass Filter per the Lab 6 Schematic (Fig. 6.1), with R26 connected to LPF_OUT (U3 pin 14).





a. MP36/MP35/MP46/MP45 CH1 signal input to LPF_OUT (U3 pin 14).

b. MP36/MP35/MP46/MP45 CH2 signal input to BP_OUT (U4 pin 8).


Software Setup


▪ Use the pre-configured BandPass.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- BandPass Template” from the lesson list and click OK.


The steps below are for Manual Graph Setup and not necessary if the pre-configured graph BandPass.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 44.


h. Enable Acquire, Plot, and Value for CH1 and CH2, and type the following labels for each channel.

i. Click “Setup” for CH1 and set parameters as follows:



Page 43 of 60 Lab 6


j. Click “Setup” for CH2 and set parameters as follows:



k. Click OK as required to exit Set up Channels.


l. Mode: Record, Save Once, Memory

m. Sample Rate: 5000

n. Acquisition Length: 5 seconds

3. Use two measurement rows. To set up, select (File > Preference > General). Show 5 measurement columns.

Show 3 digits of precision.


Page 44 of 60 Lab 6

Recording

Use the Square Wave (2.5 mVpp) output, through the InAmp (x101), High Pass Filter, Gain Block, and Low Pass Filter.


2. Record for 5 seconds.

Analysis

1. Set the following measurements for each channel: a. Freq (frequency) d) Stddev (standard deviation) b. Mean e) P-P (peak-to-peak) c. Delta T (time)

2. Generate an Output FFT.

a. Select CH2 Band Pass Out.

b. Select Transform > Difference and apply the default difference of 1 to the entire wave.

c. Click the Vertical Autoscale icon to scale the result.

d. Select one half cycle (as shown below) to simulate an impulse response for the FFT function).

e. Select Analysis > FFT (no window, other defaults ON).

f. When sampled at 5K samples per second, the FFT will show about 2.5 kHz full scale. Magnify the lower frequencies to better display the range around the 17 Hz notch.


Page 45 of 60 Lab 6

0.00 50.00 100.00 150.00Hz

45.00

60.00

75.00

90.00

105.00

dbV

Magnitu

de

3. Generate an input FFT to compare with the output FFT.

a. Select CH1 Low Pass Out.

b. Repeat steps 2b-2e to create a new FFT window.

4. Superimpose the input FFT on the output FFT.

a. Select the input FFT, select Edit > Select All, and then Edit > Copy to copy the entire input FFT waveform to the clipboard.

b. Select the output FFT, select Edit > Insert Waveform.

c. Both FFTs will be displayed in the same window.

5. Scale the FFT waveforms.

a. On the output FFT, click on the Vertical Scale, and in the Vertical Scale dialog box, enter (for example) Scale=15 dbV and Midpoint=75 dbV. Select BOTH All Channels options.

b. On the output FFT click on the Horizontal Scale and in the Horizontal Scale Dialog box, enter Scale = 50 Hz and Start = 0

c. Select the scope mode to overlap the waves.

6. Record the magnitude and bandwidth of the bandpass and compare to the design values.


Page 46 of 60 Lab 6




a. Show a graph of the input and output responses to the Band pass Filter Block, after the output has stabilized.

b. Show the FFT response of the input and output waves.

c. Discuss the design and calculated values, and explain any discrepancies between actual results and expected results.

End Lab 6


Page 47 of 60 Lab 7

Lab 7: Absolute Value Circuit for QRS Detector


Objective:

1. To construct an Absolute Value Circuit as a building block in a QRS wave detector.

Background:

In the Breadboard Lab 6, the ECG signal was processed with a Band Pass filter with a high Q of 5 and center frequency of 17 Hz to amplify the main energy band of the QRS wave. The purpose of the Absolute Value Circuit is to full wave rectify the resultant signal to produce an output that is never less than zero, to generate a TTL level output that can be used by external equipment.

The input signal at R29 arrives at a summing node of an inverting operational amplifier. A less than zero signal forward biases D2 and develops an output signal across R30, with a gain of R30/R29. When the signal is positive, D2 does not conduct. A negative feedback path through D1 is provided, which reduces the negative output swing to –0.7 V and prevents the amplifier from saturating. This is a half wave rectifier.

The second summing amplifier converts the half wave rectifier to a full wave rectifier. The second amp sums the half wave rectified signal and the input to produce a full wave signals. For negative inputs, the first amp output is zero, generating no current through R31, and the output is

28

32

R

ViRVo

−=

Positive inputs are summed through R31 and R28, so

)(2831

32R

Vi

R

ViRVo −= .

With )2

( 28

31

RR = and )(

28

32

R

RViVo =

R28=R29=R30=R32=10.0K

R31=4.99K

Laboratory:

Hardware Setup

1. Build the Absolute Value block Filter per the Lab 7 Schematic (Fig. 7.1), with BP_OUT (U4 pin 8) as the input to the block.





Page 48 of 60 Lab 7


a. MP36/MP35/MP46/MP45 CH1 signal input to BP_OUT (U4 pin 8).

b. MP36/MP35/MP46/MP45 CH2 signal input to ABS_OUT (U4 pin 1).


Software Setup


▪ Use the pre-configured ABS.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- ABS Template” from the lesson list and click OK.


The steps below are for Manual Graph Setup and not necessary if the pre-configured graph ABS.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 50.


o. Enable Acquire, Plot, and Value for CH1 and CH2, and type the following labels for each channel.

p. Click “Setup” for CH1 and set parameters as follows:



Page 49 of 60 Lab 7


q. Click “Setup” for CH2 and set parameters as follows:



r. Click OK as required to exit Set up Channels.


s. Mode: Record, Save Once, Memory

t. Sample Rate: 5000

u. Acquisition Length: 5 seconds



Page 50 of 60 Lab 7

Recording

Use the Square Wave (2.5 mV P-P) output, through the InAmp (x101), High Pass Filter, Gain Block, Low Pass Filter and the Band pass Filter.


2. After 5 seconds, press the “Stop” button.

Analysis




c. Delta T (time)

2. Compare the input to the output to verify the operation of this circuit.

3. Verify that the output is never less than zero, and that negative inputs are indeed converted to positive values.




a. Show a graph of the input and output responses to the Absolute Value Block, after the output has stabilized.

b. Show the graphs of the input and output waves.

2. Does ViVo = ? Discuss the design and calculated values, and explain any discrepancies between actual results

and expected results.

End Lab 7


Page 51 of 60

Lab 8: QRS Detection: Low Pass & System Test


Objectives:

1. To construct a Low Pass filter to remove the high frequency component of the wave generated by the QRS Band Pass filter, to produce a usable waveform that will become a QRS detector.

2. To test the ECG amplifier and QRS wave detector.

Background:

The Sallen-Key configuration of the QRS Low Pass Filter (LPF) shown in the BME ECG Amplifier schematic (the LPF that follows the Absolute Value Block) is a biquad implementation, meaning there are two poles in the circuit transfer function:

2

00

2

2

0

/

++=

QssVi

Vo

with RRR == 3433 18

2

19 4 CQC = and Qf

RC0

184

1

=

Low Pass Filter:

C18=.047uF

C19=0.1uF

R18=R19=237K

Modeling the response of an RC circuit to a step response closely approximates the cutoff frequency.

Where the voltage across the output capacitor is given as:

)1(0RC

t

eViv−

−=

The time for 0v to reach a tenth of its final value is 0.1RC, and the time to reach nine tenths of its final value is 2.3RC. rt

is the difference between these two times, so:

hh

rff

RCt35.0

2

2.22.2 ===

and r

ht

f35.0

=


Page 52 of 60

Laboratory:

Hardware Setup

1. Build the QRS Low Pass Filter per the Lab 8 Schematic (Fig. 8.1), with ABS_OUT (U4 pin 1) connected to R33 the QRS LPF input.





a. MP36/MP35/MP46/MP45 CH1 signal input to ABS_OUT (U4 pin 1).

b. MP36/MP35/MP46/MP45 CH2 signal input to QRS_OUT (U4 pin 14).


Software Setup


▪ Use the pre-configured QRS.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- QRS Template” from the lesson list and click OK.


The steps below are for Manual Graph Setup and not necessary if the pre-configured graph QRS.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 53.


v. Enable Acquire, Plot, and Value for CH1 and CH2, and type the following labels for each channel.

w. Click “Setup” for CH1 and set parameters as follows:



Page 53 of 60


x. Click “Setup” for CH2 and set parameters as follows:



y. Click OK as required to exit Set up Channels.


z. Mode: Record, Save Once, Memory

aa. Sample Rate: 5000

bb. Acquisition Length: 5 seconds



Page 54 of 60

Recording 1—LPF

Use the Square Wave (2.5 mVpp) output, through the InAmp (x101), High Pass Filter, Gain Block, Low Pass Filter, Band pass Filter and the Absolute Value Block.


2. Record for 5 seconds.

• The ABS out data shown below is clipped but could be corrected by reducing the Gain setting for the channel.

QRS LPF data

Analysis 1—LFP




c. Delta T (time)

2. Test the LPF cutoff frequency (10 Hz)

a. Select a low to high transition in CH2 Low Pass Output.

b. Magnify the time base, so that the single transition is visible across the screen.

c. Use the P-P measurement to find the total voltage of the transition, then make a Delta T measurement on a window that starts at 10% of the peak-peak range, and ends at 90%.


Page 55 of 60

ECG System

Test the ECG amplifier and QRS detector with actual ECG signals.

Hardware Setup for ECG System Test

1. Move the MP36/MP35/MP46/MP45 CH 1 signal input to ECG_OUT (U3 pin1).

2. MP36/MP35/MP46/MP45 CH2 signal input remains connected to QRS_OUT (U4 pin 14).








Page 56 of 60

9. Plug in the SS2L Electrode Assembly to the TCI-22. Connect to electrodes as follows:

a. It is a good idea to lightly abrade the skin (using an ELPAD), before electrode placement to decrease the impedance between the electrode and the skin surface.

b. b. Establish a standard Lead II configuration with three EL503 disposable electrodes: Attach the GND (BLACK) electrode on the right leg, the POS (RED) electrode to the left leg and the NEG (WHITE) electrode to right forearm.

Software Setup


▪ Use the pre-configured ECGsys.gtl graph template to simplify setup. From the Startup Wizard, choose “Create/Record a new experiment,” click the PRO Lessons tab, select “H25-H26 --- ECGsys Template” from the lesson list and click OK.


The steps below are for Manual Graph Setup and not necessary if the pre-configured graph ECGsys.gtl template is used. If using pre-configured graph template, skip directly to the Recording section on page 58.


Page 57 of 60


cc. Enable Acquire, Plot, and Value for CH1 and CH2, and type the following labels for each channel.

dd. Click “Setup” for CH1 and set parameters as follows:



ee. Click “Setup” for CH2 and set parameters as follows:



ff. Click OK as required to exit Set up Channels.


gg. Mode: Record, Save Once, Memory

hh. Sample Rate: 5000

ii. Acquisition Length: 30 seconds


Page 58 of 60


Recording 2—ECG System


• If the ECG is inverted, exchange the POS and NEG electrode connectors on the electrodes.

• If excess 50/60 Hz noise is present, adjust (firmly attach) the electrodes for better contact.

2. Insert an event marker (F9 Windows, Esc Mac) for each condition:

a. Subject touches keyboard.

b. Subject rapidly clenches/unclenches fist.

c. Subject move arm.

3. After at least 30 seconds, press the “Stop” button

• It may take up to 30 seconds for the waveform to settle (the 0.05 Hz High Pass filter).

Analysis 2—ECG

1. Need to specify ECG measurements. Note that the report asks for the effect on the ECG as Subject changes condition.

• See BSL Lessons 5-7 for more details on ECG wave analysis.


Page 59 of 60




a. Show a graph of the input and output responses to the LPF.

b. Show a graph of an expanded low to high Low Pass filter output transition, with the 10%-90% areas highlighted.

c. Show a graph of the final ECG output vs. QRS wave detection.

2. Calculate the High Pass 3db cutoff frequency and compare to the design value. Explain any discrepancies between actual results and expected results.

3. Describe how the QRS detector can be tricked. Note any problems with recording ECG waveforms.

4. Determine the rise time rt , defined as the time for the waveform to rise from 10% to 90% its final value.

5. What effect did the Subject touching the mouse or keyboard have on 50/60 Hz interference?

6. What effect did the Subject’s rapid fist clenching/unclenching have on the measurement?

7. What effect did the Subject’s arm movement have on the measurement?

End Lab 8


Page 60 of 60

Appendix:

Enabling the “Floating window” Journal Display

BSL 4.1.2 and higher: In addition to the Help menu, lesson-specific PRO Lesson PDFs are also available in the lesson’s Journal and viewable by clicking the Journal’s “lesson procedure” tab. To enhance viewing of lesson PDFs from within the Journal, BIOPAC recommends changing the Journal display preference from the default “Docked at bottom of graph window” setting to “Floating window.” This option allows for easy resizing and repositioning of the onscreen lesson Journal while allowing full access to the graph. “Floating window” also provides a higher resolution PDF display and positions any Output Control panels directly below the graph for easier viewing.

To change the Journal display to “Floating window”:

1. In BSL PRO, choose “Display > Preferences” (or click the Preferences toolbar button. ).

2. Highlight the “Journal” option in the Preferences window.

3. Under “Display Style,” select “Floating window” and click OK.

4. The Journal will now appear in a separate window from the BSL graph. (It may appear behind the graph display. Drag the graph sideways and click the Journal window to bring it to the front.

5. Click the “lesson procedure” tab to view the PDF. Reposition and resize the Journal window as necessary. Toggle between Journal text (notes you’ve entered) and the lesson procedure PDF by clicking the “Journal” and “lesson procedure” tabs.

BSL PRO Lesson H25-H26 - BIOPAC

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