Automatic Industrial Control Laboratory

Process Control Unit 1

©ITT Educational Services, Inc. Date: 04/06/2012 15

Labs

Lab 1.1: Process-Control Instrumentation

What is the purpose?

The control of processes in most industries requires accurate knowledge of process conditions, and this, in turn, requires accurate measurement of these conditions. Without measurement, there can be no error signal for the controller and no signal to the final control element for a corrective action to occur. The purpose of this lab is to familiarize you with the various devices that are used in practical process-control systems to measure conditions, develop corrective signals, and apply a corrective influence over the process. Use this opportunity to examine some real-world devices. In the textbook, the devices are represented by a symbol. There are no pictures of real-world devices. This lab will help you get acquainted with different types of sensors, actuators, controllers, and final elements.

What are the steps?

Task 1: Procedure

1. Use the ITT Tech Virtual Library or the Internet to identify the different types of devices used in a process-control system. Use the following key words to streamline your search:

o Sensors Thermal sensors Strain sensors Pressure sensors Level sensors Velocity sensors

o Process controllers PID controllers Temperature controllers Flow controllers

o Actuators Actuator motors Linear actuators Valve actuators Heaters

2. List at least three manufacturers of each device you have identified. 3. List the part ID# of each device you have listed. 4. Record the operating range of each device listed.

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5. Construct a table similar to the following one to tabulate your findings.

Devices Types of Devices

Manufacture of Device and Device No.

Operating Range

Sensors

Process controllers

Actuators

Task 2:

Procedure Group the devices you have identified in Task 1 under the following elements of the process control system:

o Measurement o Controller o Control element

Task 3:

Procedure 1. Draw and label a basic closed-loop block diagram for a basic

temperature-control system. The diagram should reflect your visualization of the elements of a loop and how the elements are connected to each other.

2. Identify devices for each block of diagram from the list you have made for Task 1 and Task 2.



Lab Report Summary

Create a lab report summary that provides supporting explanation required and answers the following questions: Did you identify the various real-world devices used in practical process-control systems?

Did you find manufacturer names and device IDs that are used in process-control systems?

Did you categorize the devices under the main elements of a process-control system?

Did you draw and label a basic closed-loop block diagram for a basic temperature-control system?

Did you identify devices for each block in the diagram that can be used in a closed-loop temperature control system?

Automatic Industrial Control Unit 2


Labs

Lab 2.1: Analog-Signal Conditioning


Signal conditioning is commonly required to facilitate the interface between various elements in a process-control system. This lab will help you investigate some of the circuits used to condition signals. You will use MultiSim to work with the following:

A Wheatstone bridge A passive filter An op amp signal conditioning circuit

What are the steps?

Task 1: Use MultiSim to build a Wheatstone bridge and an op amp instrumentation amplifier. The circuit should provide a 0-10Volt (V) output for a given range of resistance change of the active resistance in the Wheatstone bridge.

Procedure: 1. In MultiSim, build the Wheatstone bridge shown in Figure L 2.1. The

fixed resistors in this circuit are R1 = R2 = 100 Ohms (Ω) and R4 = R5 = 200 Ω. R3 is an adjustable resistor. The supply voltage, V = 12V. It is the only variable component in the circuit.

+

-

a b

R1

100

R4

200

R5

200

R3

10 R2

100

Figure L 2.1

2. Connect a volt meter between points a and b. Measure the voltage

range, while adjusting R3 between the minimum and maximum voltage values. You can adjust the value of R3 by five percent intervals by

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pressing “A” for an increase and Shift +“A” for a decrease. Record the minimum and maximum voltage values in the following table.

Minimum V Maximum V

3. Design an op amp instrumentation amplifier similar to the one shown

in Figure L 2.2. Connect it to the Wheatstone bridge such that, as R3 in the Wheatstone bridge is adjusted through a range of 0 to 10 Ω, the output voltage of the op amp changes from 0 to 10V. Hint: Refer to Example 2.20 on page 94 in the textbook for ideas.

+

-

a b

R1

100

R4

200

R5

200

R3

10 R2

100

+_

+_

+_

Figure L 2.2

Note: For op amps, use a 741 analog component and connect pin 7 to +12V (VCC) and pin 4 to –12V (VDD) on all three op amps.

4. Set R3 to 20 percent intervals and record the op amp output voltages in

the following table.

R3 Voltage 0% 20% 40% 60% 80% 100%

Task 2: Design an RC low-pass filter that will have a Vout/Vin value of less than 0.03 at 800 kilo Hertz (kHz).



Procedure: 1. Use Example 2.11 in the textbook on page 73 to help you design the

circuit. Record the critical frequency.

2. Using MultiSim, build the circuit you designed, apply a 5V sine wave signal from the function generator as the input, and use an oscilloscope to measure the output voltage for the frequencies listed in the table provided for Step 3.

3. Record the value of Vout/Vin in the table. It is a common convention to

state the output of amplifiers and filters in decibel (dB), rather than the ratio, Vout/Vin. Convert the Vout/Vin value to dB using the following equation:

in

out

V

VLogdB 20

Frequency Vout Vout/Vin dB

100 Hz 1 KHz 10 KHz 100 KHz 800 KHz

Lab Report Summary

Create a lab report summary that provides any supporting explanation required and answers the following questions. In Task 1, did the voltage between a and b change with a change in the value of

R3? In Task 1, did you get a 0V output when R3 was set to 0 percent?

In Task 1, did you get a 5V output when R3 was set to 50 percent? In Task 1, did you get a 10V output when R3 was set to 100 percent? In Task 2, did Vout/Vin decrease as the frequency of the output voltage increased? In Task 2, was Vout/Vin less than 0.03 at 800 kHz?

In Task 2, at what frequency will the output be -3dB? In Task 2, at what frequency will the output be -10 dB



Instructor Notes for the Lab Session:

The lab should be executed in groups of two to three students. Refer to Appendix G: General Information about Using Groups for more information on how to conduct labs in a group.

It is recommend that you download a copy of the datasheet for ADC0808 and

distribute it to students. A copy of pin-outs will help students in wiring the circuit. A good source of datasheets is the following Web site: Datasheets www.alldatasheet.com/ ALLDATASHEET.COM is an on-line electronic component datasheets search engine. This is a datasheet search site for electronic components, semiconductors, integrated circuits, and diodes.

Ensure that the lab is equipped with all the equipment so that students do not face any difficulty while performing their tasks.

Students should accurately follow the required steps. Missing a single step can

cause inaccurate results. Additional References

Appendix 2 on pp. 603-611 from the textbook



Labs

Lab 3.1: Digital Signal Conditioning


Many systems use digital signal processing in process control. The analog signal must be converted into a digital signal. This can be done using an ADC. In this hardware-based lab, you will use an ADC to convert an analog voltage range into digital values. You will be using an ADC 0808, which is an 8-bit microprocessor compatible ADC and has an 8 channel multiplexer. The analog channel is selected using three addressing pins. It uses a single 5V supply and outputs transistor-transistor logic (TTL)-compatible digital values.

What are the steps?

Task 1: Build an ADC circuit. Procedure

1. Build the circuit shown in Figure L 3.1. The equipment you will need are listed as follows:

o ADC 0808 o Eight 330Ω resistors o 1KΩ resistor o 10KΩ Potentiometer o LED display

Bar Graph

330 ohm

21

20

19

18

8

15

14

17

VCC

VCC

11

13

12

16

9

6

7

22

23

24

25

10CLK

26

3

Channel 0

Channel 5

ADC0808

Figure 3.1

Figure L 3.1

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2. Connect the DC power supply and a TTL-compatible clock, as shown in Figure L 3.2.

10k

1k

VCC

Figure L 3.2

3. Connect the output of the voltage divider to channel 0 and select the

channel 0 input by connecting pins 23-25 to the ground. 4. Connect a voltmeter to the output of the voltage divider and apply 5V

DC to VCC connections. Set the clock to 100 kHz.

Note: The ADC 0808 has active low outputs; therefore, when you set the input analog voltage to 0V, all LEDs will be lit, and when the analog input voltage is 5V, all LEDs will be unlit. You will read the binary output value by interpreting an unlit LED as 1 and a lit LED as 0.

5. Adjust the voltage output of the voltage divider to less than 1V, and record the binary digital output value as well as the divider voltage.

Initial binary value _____ Initial Voltage _________

6. Increase the voltage until the binary digital value has increased by

1010, and again record the binary digital value and the divider voltage.

Final binary value _____ Final Voltage _________ 7. The change in the binary value is 1010, and the change in voltage

(ΔV) is given by Vfinal – Vinitial. The resolution voltage or sensitivity is derived by the following formula:

10

V

Record the resolution voltage in Table 1.



8. Follow the same process for a voltage approximately equal to 3V and for a voltage approximately equal to 5V.

o Near 3V Initial binary value _____ Initial Voltage _________ Final binary value _____ Final Voltage _________

o Near 5V

Initial binary value _____ Initial Voltage _________ Final binary value _____ Final Voltage _________

9. Calculate the average of the three resolution voltage values. The value

you derive is the measured resolution voltage. The resolution voltage can be calculated with the following formula:

n

VCC

2VoltageResolution

In the formula, VCC is the supply voltage and n is the number of bits of the ADC.

Record your observations in the following format:

Initial Voltage

Final Voltage

Resolution Voltage

Near 1V Near 3V

Near 5V

Table 1 Resolution Voltage: Calculated ____________ Measured _____________

How close was the measured value to the calculated value?

Task 2: Predict the digital value for an analog input voltage and check the circuit

for the correct operation.

Procedure 1. Predict the digital output value by solving the following equation for D

and converting the value to an n-bit binary number:

12

n

D

VCC

V

In the formula, D is a decimal value and V is the equivalent analog



voltage after digital-to-analog conversion over n bits using a supply voltage, VCC.

Convert 2.7V to an 8-bit binary number. The binary value for 2.7V is ______________.

2. Set the voltage divider to 2.7V. Does the LED display show the correct

binary value?

3. Repeat Steps 1 and 2 for 4.2V. Does the LED display show the correct value?

The binary value for 4.2V is _______________.

Task 3: Move the voltage divider to channel 5 and reset pins 23, 24, and 25 to

select channel 5.

Procedure 1. Set the voltage divider to 1.8V. Does the LED display show the correct

value?


2. Set the voltage divider to 3.6V. Does the LED display show the correct value?


Lab Report Summary

Create a lab report summary that provides any supporting explanation required and answers the following questions. In Task 1, were the calculated and measured values within the .005V range

when the binary number was converted back into a voltage using the following formula:

12

n

D

VCC

V?

In Task 1, is the voltage drop across the 1k resistor linear over the range of the 10k resister? In Task 2, was the predicted binary value close to the circuits’ binary value?

In Task 2, what are valid reasons for the binary values to be different? In Task 3, were you able to select a different analog input channel?

In Task 3, why would you expect the values to be the same on both channels?



Labs

Lab 4.1: Thermistors


Temperature control is essential in the food processing industry, IC manufacturing processes, and metal fabrication. In this hardware-based lab, you will examine the behavior of a thermistor—one of the commonly used devices for temperature control—and use it to convert temperature into a voltage signal.

What are the steps?

Task 1: Measure the change of resistance of a thermistor as its temperature changes. You will be using the following equipment:

o 21T1K Thermistor o 741 op amp o 1KΩ potentiometer o Two1KΩ resistors o Two10KΩ resistors o Two 220Ω resistors o 180Ω if needed o 1.8KΩ resistor

Procedure 1. Set a digital multi meter (DMM) to measure resistance. Connect the

leads or the ohm meter to the leads of a thermistor. This thermistor should have a resistance of 1KΩ at 25 degrees Celsius, which is 77 degrees Fahrenheit. The room temperature will affect the resistance you measure. It will be close to 1KΩ. Record the resistance.

Thermistor resistance __________________

2. If a soldering iron is available, plug it in and heat it. After it is heated,

hold the iron near the thermistor and observe what happens to the resistance. If a soldering iron is not available, pinch the thermistor between your fingers to increase its temperature. Did the resistance increase or decrease?

The resistance _________________ (increased/decreased)

3. If canned air is available, use it near the thermistor and observe what happens to the resistance. If canned air is not available, cool your fingers with some ice or a can of pop and pinch the thermistor between your fingers to decrease its temperature. Did the resistance increase or decrease?

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The resistance _________________ (increased/decreased)

Task 2: Use the change in the resistance of a thermistor to convert a change in

temperature into a change in voltage.

Procedure 1. Construct the circuit shown in Figure L 4.1.

2. Remember to apply the positive and negative 12V to pins 4 and 7of

the op amp.

1K1K

Thermistor

220

10K

10K

220

+12V-12V

1K

1.8K

Figure L 4.1

3. Using the DMM, set it to measure voltage and connect it to the output

of the circuit.

4. Adjust the 1K potentiometer until the output voltage is 0 volts. You may have to change one of the 220Ω resistors to a 180Ω resistor to get the voltage to drop to 0V.

5. If you have a soldering iron, hold it close to the thermistor and observe the voltmeter reading. If a soldering iron is not available, heat the thermistor by holding it between your fingers to increase its temperature.

6. If canned air is available, use it near the thermistor and observe what happens to the resistance. If canned air is not available, cool your fingers with some ice or a can of pop and pinch the thermistor between



your fingers to decrease its temperature.

7. Briefly describe the effect that heating the thermistor has on the output voltage.

Note: The results of this lab are not designed to have a specific voltage for the temperature of the thermistor. A way to measure the temperature is required to get a set voltage value. It will be sufficient to note that a change in temperature will result in a change in voltage. If the temperature is measured and the change in voltage tabulated, you can develop the transfer function for this circuit. The transfer function is stated as volts per degree change in temperature.

Lab Report Summary

Create a lab report summary that provides any supporting explanation required and answers the following questions.

In Task 1, did the resistance change when the thermistor was heated? In Task 1, did the resistance change when the thermistor was cooled? In Task 1, what was the resistance range between the heated and cooled thermistor? In Task 2, were you able to set the output of the circuit to 0V at room temperature? In Task 2, if you were not able to null the system to 0V at room temperature, what

could you do to improve the circuit? In Task 2, did the voltage increase as the thermistor was heated? In Task 2, did the voltage decrease as the thermistor was cooled?



Labs

Lab 7.1: TRIAC Phase Control


There are many types of final control devices. SCRs, also called thyristors, are switching devices used in final control operations. An SCR acts like a diode. When the SCR is in conduction mode, it will continue to conduct current even after the gate signal is removed—the SCR remains in the On state until any Turn-Off condition occurs. Another limitation of SCRs is that these are unidirectional and are useful for controlling current in only one direction. To overcome this limitation, two SCRs are placed in parallel and reversed. This device conducts current in both directions, depending on the control signal on the gate. This device is called a TRIode for Alternating Current (TRIAC). The purpose of this lab exercise is to provide you experience in using the TRIAC as a final control element. In this lab, you will:

Control the power to an AC load using a TRIAC Adjust the load power over a given range of resistor values.

What are the steps?

Task 1: Build a TRIAC phase control final control circuit. Procedure

1. Obtain the datasheet on the SC141B TRIAC and determine the pin out and the threshold voltage.

2. Build the circuit shown in Figure L 7.1. The following list shows the

equipment you will need: o SC141B TRIAC o 1kΩ potentiometer o 12V lamp o 10Ω resistor o 0.47μf capacitor

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Figure L 7.1 3. Apply the 12.6VAC to the circuit.

Note: The 12.6VAC supply will be from the output of the 12.6VAC step down transformer supplied in the lab room.

4. Connect an oscilloscope with the positive lead to MT2 and the negative lead to MT1, and observe the waveform. The waveform will show the voltage across the TRIAC as shown in Figure L 7.2.

Figure L 7.2

Task 2: Observe how the power dissipated by the load—the lamp—changes as

the value of R1 changes. Procedure

1. Adjust R1 and observe how the waveform changes. You will notice that, as the value of R1 changes, the waveform changes from a full sin wave to almost a flat line. You will also observe that when the waveform is a full sin wave, the lamp will not be lit. As the waveform shape changes to almost a straight line as shown in Figure 2, what



happens to the lamp?

2. Use the DMM set to measure AC current and insert the meter in series with the lamp.

3. The portion of the waveform where the sin wave is shown occurs when the TRIAC is Off, and the portion of the waveform that is flat indicates that the TRIAC is On. Adjust the waveform shown on the oscilloscope so that the TRIAC is On for about 50 percent of the positive half cycle. Record the current through the lamp. Then use the DMM to measure the AC voltage across the lamp.

Lamp Current _____________ Lamp Voltage ____________

4. Adjust R1 until the TRIAC is on for about 75 percent of the positive

half cycle and record the current through the lamp and voltage across the lamp.

Lamp Current _____________ Lamp Voltage ___________

5. Adjust R1 until the TRIAC is always on and record the current through

the lamp and the voltage across the lamp.

Lamp Current ___________ Lamp Voltage _________

6. For the three settings of R1, calculate the power dissipated by the lamp.

Power for 50% _______________ Power for 75% _______________ Power for always on _____________

Lab Report Summary


In Task 1, draw the predicted waveform across the lamp. In Task 2, was the lamp voltage greater in Step 5 than it was in Step 3? In Task 2, was the lamp current greater in value in Step 5 than it was in Step 3? In Task 2, was the power dissipated by the lamp greater in Step 5 than it was in either

Step 3 or Step 4? In Task 2, would a 20% change in time that the TRIAC is on result in a 20% change

in power applied to the lamp? Explain your answer and provide calculations to support your conclusion.



Labs

Lab 8.1: Analog Controller Circuits


The controller is the part of the process-control system, which inputs the controlled variable and a setpoint representing the desired value of the variable. The controller outputs a signal representing action to be taken when the measured value of the controlled variable deviates from the setpoint. The deviation is called an error. In this lab, you will build controller circuits and observe the controller output signals for various controller modes. You will do this lab exercise using MultiSim.

What are the steps?

Task 1: Build an analog PID controller in MultiSim. Procedure

1. Build the circuit shown in Figure L 8.1 using MultiSim.

Figure L 8.1

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Use the following component values: o R = 10kΩ o R1 = 10kΩ o R2 = 47kΩ o R3 = 1.3kΩ o RI = 3.3kΩ o RD = 82kΩ o CI = 100nF o CD = 4.7µF

2. Use 5V for the VCC and VEE to the op amps, and set up a switch to

input at Ve so that the error input can be changed using the switch. The Multisim circuit should now look like Figure L8.2.

R1

47kR2

10k

V110mV

V210mV

J1

Key = Space

U2

741

3

2

4

7

6

51

VEE

-5V

VCC5V

U1

741

3

2

4

7

6

51

R3

10k

R4

10k

VEE

-5V

VCC5V

U3

741

3

2

4

7

6

51

VCC5V

VEE-5V

U4

741

3

2

4

7

6

51

VCC

5V

VEE-5V

R7

1.3k

R5

3.3k

R6

82k

U5

741

3

2

4

7

6

51

R8

10k

R9

10k

R10

10k

R11

10k

XSC1

A B

Ext Trig+

+

_

_ + _

C1

100nF

C2

4.7uF

Proprotional Controller

Integral Controller

Derivative Controller

Remove these lines for Step 1 of task 2

Figure L 8.2

3. Set the V1 and V2 voltages to 10mV and connect the oscilloscope to the output.



Task 2: Observe the characteristics of various controller modes. Procedure

1. To observe the characteristics of a proportional controller, remove the connecting lines that join the integrator and the differentiator to the summing amplifier. Run the simulation and observe the oscilloscope as you toggle the switch from one supply voltage to another. Print the oscilloscope waveform using the print instrument feature. Label the printout to indicate which controller mode is referred to.

2. Change the gain of the proportional controller by changing the value of R2 shown in Figure 2. Print and label the oscilloscope display for the simulation.

3. Connect the integrator circuit to the summing amplifier. This makes a proportional-integral controller. Run the simulation and observe the waveform on the oscilloscope while you switch the input. You may have to adjust the oscilloscope sweep speed to observe the effect; however, you will notice that the proportional-integral controller responds differently than proportional controller, to the change in the input. Print the oscilloscope waveform. Change the CI value to 10nF, run the simulation, and print the waveform. Observe how the waveform changes with variation in the integral gain.

4. Connect the differentiator circuit to the summing amplifier, run the simulation, and print the oscilloscope waveform. Change the CD value to 1µF and print the oscilloscope waveform. Observe the effect of changing the derivative gain.

Note: These oscilloscope waveforms are not the output of a controller

that is used in a closed-loop process-control system. These waveforms represent the behavior of a controller responding to a voltage input in an open-loop condition.

5. Use printouts of waveforms and write a short conclusion describing the behavior of the three controller modes you simulated.

Lab Report Summary


1. In Task 2 Step 1, did the output waveform of the proportional controller give a square wave that followed the change in the input switch?

2. In Task 2 Step 3, after the integrator was added, did the output waveform of the proportional-integral controller give a waveform that had a linear slope?



3. In Task 2 Step 4, after the differentiator was added, did the output waveform jump toward 0V when the input switch was changed?

Automatic Industrial Control Laboratory

Documents

process control system

control of processes

final control element

various devices

o sensors thermal sensors

different types of devices

various realworld devices

pictures of realworld