42-0157-00 Low Ash Sensitivity Pm-147 Sensor

8/6/2019 42-0157-00 Low Ash Sensitivity Pm-147 Sensor

1/25

VOITH

MANUALLOW ASH SENSITIVITY PROMETHIUM-147

BASIS WEIGHT SENSORMODEL 4403-3

PN: 42.0157.00


2/25

LOW ASH SENSITIVITY PROMETHIUM-1BASIS WEIGHT SENSOR MANUAL

VOITH PAPERAUTOMATION

Contents:

1. Sensor Overview

2. Sensor Description2.1 Operating Principle and Measurement Algorithm2.2 Sensor Electronics2.3 Cooling System and Purge Air 2.4 Air Column Temperature Measurement and the Air Curtain2.5 Sensor Wiring

3. Troubleshooting

4. Window Replacement4.1 Source Window4.2 Receiver Window

5. Shutter Operation

6. Basis Weight Calibration6.1 Overview6.2 Initial Dynamic Calibration6.3 Continued Dynamic Basis Weight Verification

7. Leakage Radiation

8. Spare Parts

PN: 42.0157.00 Page2REV 1


3/25


1. Sensor Overview

The Impact Basis Weight Sensor measures the basis weight of paper using the absorption

of -rays from a radioactive source. This source contains 500 mCi (18.5 GBq) of Promethium-147.

Figure 1.1 shows the transmission curve for Promethium-147.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

g/m2

S i g n a l

Figure 1.1. Transmission Curve for Pm-147

Promethium-147 source is used for basis weights up to 250 g/m2. The half life of Pm-147 is 2.6 years and the recommended working life for the source is 5 years.

After the working life of the source has expired, the source needs to be replaced by a person trained by Impact and properly authorized to work with radioactive sources.Radiation safety issues are covered in a separate manual.

PN: 42.0157.00 Page3REV 1


4/25


Source/Shutter

Sheet

Silicon Detector Array

Pre-Amp.

Internal Standard

VFC

Figure 1.2 Basis Weight Sensor Block Diagram

PN: 42.0157.00 Page4REV 1


5/25


The Pm-147 source is mounted on a rotating source holder that acts as a shutter bymoving the source in and out of the measuring position.

An internal mylar standard can be inserted in front of the source. This standard is used toimprove dirt compensation and to verify calibration stability automatically.

The receiver has a four element Silicon detector array mounted on a temperaturecontrolled platform. Detectors are connected to a preamplifier and a voltage to frequencyconverter.

Both the source and the receiver heads have a air circulation system that will keep the air behind the external window in rapid motion. A venturi is used to keep the air flowingthrough a tube containing an air temperature sensor. The signal from this temperaturesensor is used for calculating the air density compensation for the internal air columns.

The external air gap is purged from both sides of the sheet with a circular air curtainsurrounding the window area. The spent sensor cooling air flows through a temperaturecontrolled plenum into this curtain.

2. SENSOR DESCRIPTION

2.1 Operating Principle and Measurement Algorithm

As the radiation penetrates the sheet, it will interact with the charged particles in thematter in several ways. Beta rays can lose energy by colliding inelastically with theelectrons in the atoms. In this case the beta ray will not only slow down, but it will alsochange direction, i.e. it will scatter. A beta particle can also collide with the atomicnucleus elastically, in which case it will scatter without a loss of energy. A small amountof a beta particles energy is also lost as the electromagnetic field around the atoms willcause the particles to decelerate and emit X-rays (bremsstrahlung).

The absorption of beta energy by matter is generally proportional to the density of electrons in the matter. For all common elements, with the exception of hydrogen, themass number of an atom is close to two times the number of electrons in the atom, so themass absorption coefficient for a beta ray with a given energy is almost independent of the element. Hydrogen, of course, has one electron and a mass number of one, so anymaterial with a high Hydrogen content will have a high absorption.

Elastic scattering increases with increasing mass number. Even through there is noenergy loss, the elastic scattering increases the average path through the sheet, andtherefore increases the absorption by the inelastic collisions. A beta sensors ashsensitivity is primarily a result of the increased elastic scattering by the heavier elements

PN: 42.0157.00 Page5REV 1


6/25


in ash. Impacts sensor is compensated for ash variations by the proper selection of source and receiver geometry.

Increasing basis weight reduces the average energy of the beta particles, and theabsorption coefficient increases with lower energy. This means, that if the sensor windows get dirty thus increasing the total mass, the sensor will become marginally moresensitive requiring a small correction. Impacts basis weight sensor is equipped with aninternal standard that is used to calculate this correction.

Since the beta absorption does not accurately obey Beer's law, the calculation algorithmused by Impact is somewhat complex.

2.1.1 On-sheet Algorithm

(1) BW0=A+B*x+C*x 2+D*x 3- (xf K)*(H*x+I*x 2+J*x 3) + E*Uacc +F*Lacc

(2) BW=Slope*BW0+Offset

Where: Slope and Offset are grade dependententries from the supervisory system.

A through K are gauge constants.

Uacc and Lacc are the upper and lower air column density correction factors.

BW is the basis weight in g/m2.

(3) x=ln[(I0-IB)/(I(n)-IB)

(4) xf=ln[(I0-IB)/(Ifl-IB)

Where: I0 is the signal at STDZ with the shutteropen and IB is the STDZ signal with the

shutter closed with a correction for theX-ray background.

Ifl is the signal with the internal standard.

ln in formula (3) means natural logarithm.

(5) I(n) = PROF(n)*IACT(n)

Where: PROF(n) is the air profile correction factor for data box n. (See 2.1.3)

PN: 42.0157.00 Page6REV 1


7/25


IACT is the actual on-sheet signal withoutany corrections

2.1.2 Standardization (STDZ)

A. Home Standardization

This form of standardization is done in home position, either by requestor based on time.

Phase 1: Open the shutter. Read and average thesensor signal for 5 seconds. This average will bethe new I0.

Phase 2: Insert the internal standard into the beam. Read andAverage the signal for 5 seconds. This average will

be the new If.

Phase 3: Close the shutter. Read and average the sensor signalfor 5 seconds, this reading is used to calculate IB.

B. Edge Standardization

The edge standardization is used to update open shutter reading every time the sensor crosses the edge of the sheet in order to continuously compensate for dirt accumulation.

PN: 42.0157.00 Page7REV 1


8/25


2.1.3 Air profile correction

Air profile correction is used to correct possible errors in the scanner alignment. Thecorrection array is created by scanning with an open shutter and empty gap over the

maximum scan range, and by calculating the following expression for each data box:(5) PROF(n) = I0(home)/I0(n)

where: I0(home) is the sensor signal with openshutter in the home position, and I0(n)is the signal at data box number n.

In order to obtain a valid I0(home), the air profile measurement sequence starts with ahome standardization.

Air profile correction measurement normally scans ten times in each direction and thengoes off sheet and calculates arithmetic averages for the correction factors. It is, however,sometimes necessary to terminate the process early by pushing the off sheet button. Thesystem will then calculate the averages using a lesser number of scans (minimum one eachway).

Initially all values in the correction array are set to one.

2.1.4 Set-up Data

PN: 42.0157.00 Page8REV 1


9/25


This version of the basis weight sensor is supported by the Aplus version 3.0 or higher.The key basis weight related items in v3.0 are:

aplus.sensor.bw.stdzOpenLimits: 30000.0 220000.0 # low, highaplus.sensor.bw.stdzCloseLimits: 1.0 350.0 # low, highaplus.sensor.bw.basisWeightLimits: 10.0 300.0 # low, highaplus.sensor.bw.flagLimits: 15000.0 40000.0 # low, highaplus.sensor.bw.coeA: 0.16 # coeAaplus.sensor.bw.coeB: 55.88 # coeBaplus.sensor.bw.coeC: -3.929 # coeCaplus.sensor.bw.coeD: 0.2438 # coeDaplus.sensor.bw.coeE: -16.5 # Upper air comp.aplus.sensor.bw.coeF: -8.5 # Lower air comp.aplus.sensor.bw.coeG: 0.006953 # Background comp.aplus.sensor.bw.coeH: 36.7687 # Dirt curve 1 st power aplus.sensor.bw.coeI: -1.9371 # Dirt curve 2 nd power aplus.sensor.bw.coeJ: -1.8287 # Dirt curve 3 rd power aplus.sensor.bw.coeK: 2.12044 # Clean xf

The new sensor open counts are higher than the old model had, the range is now up to250000. Typically the open counts are set to be just below 200000. Typical value for flagcounts is 25000. Closed counts are set to approximately 200.

2.2 Sensor Electronics

2.2.1 Preamplifier (05-1142-00)

The detectors operate with zero bias voltage. Each of the four detectors has a separatefront end preamplifier with an offset adjustment. These offsets are factory adjusted toapproximately 1 mV. These adjustments are used to control the closed sensor outputsignal. The signals from the input amplifiers are then filtered with a 6 th order low passfilter with a 3 dB point at 1 kHz, and then combined in a summing amplifier to form theoutput signal to the VFC. The summing amplifier has an adjustable gain. This gainadjustment is highly linear and has no influence on sensor calibration. It is used to bringthe signal levels back up for older sources to maintain high signal resolution.

2.2.2 Voltage to Frequency Converter (05-1137-00)

Voltage to frequency converter board has a 0 to +5 V input corresponding to a 0 to 200kHz output. The analog basis weight signal from the 05-1142-00 board J6-1 is connectedto the VFC board J1-1, converted to a frequency signal, and transmitted from the VFC

board connector J2 pins 1 and 2 to the sensor connector pins D and E.

2.2.3 Temperature Control Board (05-1112-01)

The temperature control board keeps the area around the window inside the basis weightsensor at a constant temperature, heats the sheet guide to prevent condensation, and

PN: 42.0157.00 Page9REV 1


10/25


provides the air column temperature measurement. This board is used in both the upper and the lower head.

The window area temperature control uses a PT-100 type Platinum resistor temperaturetransducer to measure the temperature. A similar temperature sensor is used in the air space behind the sensor window to measure the air column temperature.

U2 amplifies the temperature signal (set point deviation) and switches the heaters on andoff as required via transistors Q1 and Q2. Temperature set point is selected with jumper JA as shown on the schematic.

Air column temperature is measured with a semiconductor temperature sensor. Thesignal from this temperature sensor is converted to a frequency signal with U5, andtransmitted to the computer frequency input from the line driver U4. The outputfrequency is approximately 30 kHz at room temperature and increases 0.35%/ oC withincreasing temperature.

2.2.4 Detector Temperature Controller (P/N 05-1117-01)

This board controls the temperature of the four detectors using a Peltier cooler and asemiconductor temperature sensor as a feedback element. The detector temperature iscontrolled to be approximately 25 oC.

The board has four bridge circuits that measure the detector temperature. These signalscontrol the cooling with four current drivers. All four coolers are connected in series.One of the current drivers controls the overall current through all Peltier coolers usingthe Darlington pair Q1&Q2, the other three drivers provide a small balance adjustmentcurrent for three of the coolers.

PN: 42.0157.00 Page10REV 1


11/25


2.3.5 DC-DC Converter Board (P/N 05-1124-00)

The function of the DC-DC converter board located in the lower (receiver) head is to provide +15 V, -15 V, and +5 V for the sensor electronics. The power input to the sensor is +24 Vdc.

2.3 Cooling System and Purge Air

The cooling system for this sensor utilizes a vortex cooler inside each sensing head.Vortex cooler produces a cold air flow and a hot air flow. Cold air is fed to a cooling coiland heat exchanger inside each sensing head, and from there to an external outlet fitting.This cold air outlet is available for other sensors that may need cooling. From theseother sensors the spent cooling air is looped back through the return fitting to the air curtain, where it is combined with the hot air from the vortex cooler.

A removable plug on the air manifold connected to the hot end of the vortex cooler

provides access to the cooler adjustment screw at the end of the cooler. The vortex cooler is adjusted to maximum power by turning the adjustment screw until the hot end of thedevice is as hot as possible.

The inside of the sensor is purged with clean, dry instrument air through a separate 4 mmfitting. This purge air also drives the venturi that is used for the internal air columncirculation in each head.

PN: 42.0157.00 Page11REV 1


12/25


2.4 Air Column Temperature Measurement and the Air Curtain

The density of the air between the source and the detector will influence the sensor reading, unless it is compensated for. Standardization will correct the effect of the air density variations as long as there are no temperature or humidity variations betweenstandardizations. The Impact basis weight sensor measures the empty gap at each scanturn-around, so in normal scanning operation the variations in the density of air in theinternal air column is negligible. The external air gap is protected from temperature andhumidity variations by the air curtain.

Even though the effect of the air density variations is very small during normal scanning,significant errors can occur when the sensor is used either in the single point or in thesample mode. To eliminate the air density related errors for these cases, the internal air columns on both sides of the measuring gap are purged through a suction tube connected

to a venturi. Inside this suction tube is a semiconductor temperature sensor (AD590). Thesuction system replaces the air in the air column rapidly, thus preventing rapidtemperature changes due to sheet temperature variations, and the temperature sensor willmeasure the temperature of this air for an accurate software compensation.

The external air gap is protected from density variations by the air curtain surroundingthe window area. This air curtain will keep the air in the measuring beam between thesource and receiver windows dry and at a nearly constant temperature. All of the sensor cooling air is fed into this curtain through a temperature controlled plenum.

PN: 42.0157.00 Page12REV 1


13/25


2.5 Sensor wiring

2.5.1 Source Wiring

The source head connector signals are:

A N/CB N/CC N/CD N/CE N/CF N/CG N/CH Upper Air Column Temperature+J Upper Air Column Temperature-

K Shutter Switch1+ (Common)L Shutter Switch1- (N/O)M Flag Drive (+24V off, 0V on)

N +24 VdcP GNDR N/CS N/CT N/C

Internally the Upper Air Column Temperature+ is connected to 05-1112-01 TB2-3 andthe Upper Air Column Temperature- is connected to 05-1112-01 TB2-4.

The air column temperature sensor + is connected to 05-1112-01 TB2-2 and to 05-1112-01 TB2-1.

The radiation lights mounted on the source head are connected to a second shutter switch, the return wire from both lamps is connected to ground, the red lamp is drivenfrom Shutter Switch2 (N/C) and the green lamp is driven from the Shutter Switch2(N/O). Shutter Switch2 (Common) is connected to +24 Vdc at the source head connector

pin N.

The temperature control board 05-1112-01 is powered from source connector pin Nconnected to 05-1112-01 TB1-7 and from source connector GND pin P connected to 05-1112-01 TB1-8.

The air curtain heater is connected to 05-1112-01 TB1-1 and TB1-2 and the face plateheater is connected to 05-1112-01 TB1-3 and TB1-4. The temperature feed-back (Pt-100) from the air curtain heater is connected between 05-1112-01 TB1-5 and TB1-6.

2.5.2 Receiver Wiring

PN: 42.0157.00 Page13REV 1


14/25


The receiver head connector signals are:

A N/CB N/C

C N/CD BW+E BW-F N/CG N/CH Lower Air Column Temperature+J Lower Air Column Temperature-K N/CL N/CM N/C

N +24 VdcP GNDR N/CS N/CT N/C

Temperature control board 05-1112-01 is powered from receiver connector pin Nconnected to 05-1112-01 TB1-7 and from receiver connector GND pin P connected to05-1112-01 TB1-8.

Internally the Lower Air Column Temperature+ is connected to 05-1112-01 TB2-3 andthe Lower Air Column Temperature- is connected to 05-1112-01 TB2-4.

The air column temperature sensor + is connected to 05-1112-01 TB2-2 and to 05-1112-01 TB2-1.

The air curtain heater is connected to 05-1112-01 TB1-1 and TB1-2 and the face plateheater is connected to 05-1112-01 TB1-3 and TB1-4. The temperature feed-back (Pt-100) from the air curtain heater is connected between 05-1112-01 TB1-5 and TB1-6.

PN: 42.0157.00 Page14REV 1


15/25


Other internal receiver connections:

05-1124-00From: To:

J1-1 Receiver Connector NJ1-2 Receiver Connector PJ2-3 05-1142-00 J7-3J2-4 05-1142-00 J7-4J2-5 05-1142-00 J7-5J2-6 05-1142-00 J7-6J3-2 05-1137-00 J4-2J3-3 05-1137-00 J4-3J3-4 05-1137-00 J4-4J3-5 05-1137-00 J4-5J3-6 05-1137-00 J4-6J6-1 05-1117-01 J1-1J6-2 05-1117-01 J1-2J6-3 05-1117-01 J1-3J6-4 05-1117-01 J1-4J6-5 05-1117-01 J1-5J6-6 05-1117-01 J1-6

05-1117-01J1-1 05-1124-00 J6-1J1-2 05-1124-00 J6-2J1-3 05-1124-00 J6-3J1-4 05-1124-00 J6-4

J1-5 05-1124-00 J6-5J1-6 05-1124-00 J6-6J2-1 Detector Connector pin 2J2-8 Detector Connector pin 1J3-1 Detector Connector pin 3J3-8 Detector Connector pin 4

PN: 42.0157.00 Page15REV 1


16/25


05-1142-00J7-3 05-1124-00 J2-3J7-4 05-1124-00 J2-4J7-5 05-1124-00 J2-5J7-6 05-1124-00 J2-6J6-1 05-1137-00 J1-1J6-2 05-1137-00 J1-2J1 Detector 1J2 Detector 2J3 Detector 3J4 Detector 4

05-1137-00J1-1 05-1142-00 J6-1J1-2 05-1142-00 J6-2J2-1 Receiver Connector pin DJ2-2 Receiver Connector pin EJ4-2 05-1124-00 J3-2J4-3 05-1124-00 J3-3J4-4 05-1124-00 J3-4J4-5 05-1124-00 J3-5J4-6 05-1124-00 J3-6

PN: 42.0157.00 Page16REV 1


17/25


3. TROUBLESHOOTING

The primary tool for troubleshooting this sensor is the record of standardizations andstandard sample readings. Both open and closed sensor frequencies, as well as basisweight readings for the standard samples provided with the sensor must be recorded at

regular intervals. Large sudden changes in the standardization readings are often an earlyindication of a problem, even though the actual basis weight readings may not initiallychange.

A significant rapid drop (>15%) in the open sensor frequency is often caused by dirt build-up on the windows, but it can also be caused by faulty sensor electronics, a looseconnection, a faulty frequency input in the Aplus, or a shutter that is not opening fully.Open sensor frequency is initially adjusted to 190 kHz +/- 10 kHz.

A change in the flag (internal mylar standard) reading is also normally caused by dirt onthe windows. It can also be an indication of dirt build-up on the flag itself due to dirty

purge air. Malfunctioning flag valve, flag actuator cylinder, or the flag drive system canalso be the cause for flag readings.

A change in the closed sensor frequency of more than 200 Hz is caused either by anelectronic failure or, if there is a problem with the purge air, condensation or oil insidethe sensor. Normal values for the closed sensor frequency range from 50 Hz to 500 Hz.

A malfunction of the shutter or the flag in the upper head can cause significant changesin the standardization values. The minimum air pressure required for the reliableoperation of the shutter and flag actuators is 35 psig (340 kPa). If the shutter fails toclose completely, the open sensor frequency will be high. This condition will beindicated by the shutter warning lights remaining red, both on the upper basis weight

head, and on the scanner. A shutter that opens only partially will cause the red lights tocome on. The meaning of the red light is not fully closed, thus, the red light cannot berelied upon as an indicator of a properly functioning shutter.

If the shutter fails to close completely, Impact personnel needs to be notifiedimmediately and the system must be left in the park position.

4. WINDOW REPLACEMENT

PN: 42.0157.00 Page17REV 1


18/25


4.1 Source Window Replacement

1. Push the off sheet button and wait till the scanner has fully stopped.

2. Push the service button and allow the heads to move to the service position.

3. Check that the radiation warning lights both on the source heads and onthe scanner are green. If lights are not green, send the heads off sheetand call for service. Do not attempt to replace the window unless alllights are green.

4. Assuming the lights were green, remove the window assembly from thesource head by opening the five M3 screws, then push the old window and theaperture plate out of the window holder.

5. Place a new Mylar window into the cartridge, place the aperture plate over thewindow, and fasten the window assembly into the source head with the five M3screws.

6. Push off sheet button to bring the sensing heads back together.

PN: 42.0157.00 Page18REV 1


19/25


4.2 Receiver Window Replacement

1. Push the off sheet button and wait till the scanner has fully stopped.

2. Push the service button and allow the heads to move to the service position.

3. Check that the radiation warning lights both on the source heads and onthe scanner are green. If lights are not green, send the heads off sheetand call for service. Do not attempt to replace the window unless alllights are green.

4. Assuming the lights were green, turn off scanner power and air, and remove thewindow holder from the receiver head by opening the six M1.6 screws, thenremove the old window. Leave the aperture plate on the receiver head.

5. Place a new Titanium window on the aperture plate, center the window and theaperture plate, and place the window holder over the window. Make sure the twocutouts on the inside of the window holder line up in the machine direction. Thisis required for the air curtain to function properly. When the window holder isaligned, fasten it into the receiver head with six M1.6 mounting screws.

6. Turn power and air back on to restart the scanner.

SHUTTER OPERATION

PN: 42.0157.00 Page19REV 1


20/25


The following diagram shows the shutter controls, radiation warning lights and interlock circuits.

Figure 5.1. Shutter Control Circuits

PN: 42.0157.00 Page20REV 1


21/25


6. BASIS WEIGHT CALIBRATION

6.1 Overview

This procedure is intended to provide a basis for establishing consistent and verifiablemeasurement with the Impact Basis Weight Sensor in the mill environment.

Initially the gauge must be correctly aligned and adjusted (HVadjustment).

The sensor is supplied with a set of factory calibration constants. These calibrationconstants are based on mylar standards.

The final calibration and calibration verification is based on dynamic sampling.

The dynamic sensor calibration consists of two steps, the initial calibration that is done,when a new sensor is commissioned, and the routine ongoing calibration verification.

During the initial calibration both slope and offset values are established for the various paper grades. (Often only the slope is used at this stage).

The purpose of the on-going calibration verification is to make sure that the calibrationremains correct. At this stage, only small corrections are made to the calibration, andtypically only the offsets are changed based on the dynamic sampling.

6.2 Initial Dynamic Calibration

The preferred method for basis weight dynamic calibration is based on comparing theroll average basis weight from the reel report to the average basis weight of thecorresponding rolls from the rewinder.

This roll weight method is far more accurate than any method based on reel samples,assuming that an accurate length measurement as well as an accurate shipping scale areavailable.

The alternative method is based on single pointing the sensor to a selected location on the

sheet, where both CD and MD variations are small, logging the data just before the reelturn up and the cutting laboratory samples from the reel at the selected location. For the best accuracy it is important to time the sampling precisely for proper comparison withthe data logger.

The factors that often make this latter method relatively inaccurate, are formation, rapidMD variations and the conditioning of the sample moisture.

PN: 42.0157.00 Page21REV 1


22/25


6.2.1 Roll Weight Method

Procedure

1) Obtain the rewinder report and the Impact reel report.2) Calculate the average basis weight using the roll weight, the

roll width, and the length of paper in the roll.

Basis weight equals the roll weight divided by the area of paper in the roll. The area is the roll width times thelength. Apply appropriate unit conversion.

3) Compare Impact reel average with the calculated basis weight.

6.2.2 Reel Sample Method

This procedure is based on single pointing the sensor to a selected location on the sheet,where both CD and MD variations are small, logging the data just before the reel turn upand the cutting laboratory samples from the reel at the selected location. For the bestaccuracy it is important to time the sampling precisely for proper comparison with thedata logger.

1) Select a location, on the sheet, where the basis weight is relative stable,in both MD and CD directions, and single point the sensors at thislocation.

2) Measure the distance from the sensor window center line to the edge of the sheet. Record this distance.

3) Make sure you have all necessary equipment ready and the machineoperator prepared to take a sample from the reel. Just before taking thesample, single point the sensors at the selected location and turn on thedata logger.

4) Cut a sample (several layers of paper) at the correct location. Make surethat the sample is significantly larger than the die that will be used to cut

the samples to final size in the laboratory.5) Throw away the top and bottom sheet, and quickly place the sample in

the sample bag. The bag should be closed with a minimum amount of air around the sample to prevent changes in the sample moisture.

6) Prepare a scale for quick sample weighing.

PN: 42.0157.00 Page22REV 1


23/25


7) Remove the sample from the bag cut it quickly to the proper size andweigh it rapidly. Make sure that you don't spend more than a fewseconds in the process, otherwise the sample conditioning will spoil theaccuracy. Convert the reading to appropriate units.

8) Read the basis weight from the data logger printout and compare it withthe laboratory value.

Initial Slope and Offset Adjustment

The calculation of new slope and offset values is done by first graphing the laboratorydata for a given grade as a function of the sensor readings and by finding the best fitstraight line for the points on this graph. The most convenient way to determine the slopeand offset is to use a suitable spreadsheet program, such as Excel, and use thespreadsheet tools to fit a linear trend line to the data. The graph below was made usingExcel.The slope and offset of this line are then used to determine the new calibration data. Thedata must cover a wide range of basis weight values within a grade with goodrepeatability before both slope and offset can be determined.

Figuring the slope and offset:

y = 1.0197x - 1.8649

0

10

20

30

4050

60

70

80

90

0 20 40 60 80 100

Sensor

L a

b .

If your slope and offset for data collection were not Slope = 1, Offset = 0, then you mustuse the following to adjust the slope and offset calculated from your data:

New Slope= Old Slope x Slope from Graph

New Offset= (Old Offset x Slope from graph) + Offsetfrom graph

PN: 42.0157.00 Page23REV 1


24/25


If the data is only covering a narrow range of values, it is not advisable to try to calculate both the slope and the offset. In those cases it is best to set the offset to zero and adjustonly the slope for the initial grade calibration. For the continued fine tuning later on,only the offset should be used.

6.3 Continued Dynamic Basis Weight Verification

Basis weight calibration should be verified periodically after the initial calibration. Thefrequency of recheck will be necessarily determined by the variations of the process andmill requirements. Typically a verification is recommended after major service or repairs to the basis weight sensor, or after the sensor standardization values changesignificantly.

The sensor data is collected in the same manner as the it was done for the initial dynamiccalibration.

If after adequate number of samples it becomes apparent, that the calibration needs to beadjusted, calculate the average of the laboratory readings and the average of the gaugereadings and calculate the correction using the following formula:

New Offset = Old Offset + (Lab. Average - Sensor Average)

The new offset must be entered to the grade calibration tables in order to make thechange permanent.

Normally it is not necessary to adjust the slope, unless the sensor has undergone major repairs.

PN: 42.0157.00 Page24REV 1


25/25


7. LEAKAGE RADIATION

Promethium-147 source is an almost perfectly pure source of soft beta radiation. This beta radiation is completely stopped by a 0.5 mm (0.02) sheet of plastic. Unfortunately beta radiation will always generate X-rays with approximately the same energy as the beta particles that caused them. It is these X-rays that can be detected outside the sensor in small amounts even with the shutter closed. With the shutter closed and the sensingheads separated for service, the maximum radiation level is found on the surface of thesource window, a typical dose rate is approximately 1 mrem/h. The levels are nearlyundetectable anywhere away from the immediate window area. With the sensor inoperation with the shutter open, the maximum dose rate in the accessible areas is found atthe radiation light end of the measuring gap. The dose rate there is typically less than 1mrem/h.

8. SPARE PARTS

The following spare parts are recommended:

P/N Description05-1112-01 Temperature Control Board05-1117-01 Detector Temperature Controller 05-1124-00 DC-DC Converter Board05-1137-00 Voltage to Frequency Converter

05-1142-00 Four Channel BW Preamplifier 51-0287-00 Indicator Lamp (Radiation Lights)25-0101-00 Venturi051-0438-00 Micro-switch08-4502-00 Mylar Window for the source head08-4501-00 Titanium Window for the receiver head08-4507-00 Temperature Sensor Assembly70-3001-03 M3 source window mounting screws70-1002-23 M2 receiver window mounting screws70-1003-12 M4 side cover mounting screws

PN 42 0157 00 P 25

42-0157-00 Low Ash Sensitivity Pm-147 Sensor

Documents