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CRC -15W Application Note 5132-5031 Rev. B
Well Detector Manual Re-Calibration 1
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Purpose/Scope ®
To provide a procedure to perform a manual calibration of the CRC -15W Well Detector when Auto-Cal will not bring the unit into calibration. The Factory Setup Password is not for general distribution to the end user.
Note:
2
Procedure 2.1
The following items are required to perform a manual ca libration: ®
CRC -15W Calibrator
Cs137 Rod Source
Printer with Serial Printer Cable (Optional)
2.2
If the optional printer is part of the system, verify the printer connection to the port on the back of the CRC-15W labeled “PRINTER”. “PRINTER”. Be sure the connectors are screwed screwed into place on the units.
2.3
Reset the Cal Factor to 1.000 by using the following steps:
2.4
2.3.1
Turn on the power.
2.3.2
Press the ENTER key. key.
2.3.3
Press UTIL, 9, 5, SPC, 1, 3 and ENTER .
2.3.4
Select COUNTER. COUNTER.
2.3.5
Select CAL FACTOR. FACTOR. Press 6(N) to answer NO to “Correct?”.
2.3.6
Input 1.000 using the number keys. Press ENTER when when done.
2.3.7
Press 9(Y) to answer YES to “Correct?”.
2.3.8
Press the HOME key.
Reset the Gain Reference Number to 128 (the center of the adjustment ad justment range) by using the following steps: 2.4.1
Press the WELL key.
2.4.2
UTIL may need to pressed twice if no background Press the UTIL key. ( UTIL measurement was performed)
2.4.3
Select SETUP . The “PASSWORD:” screen appears.
2.4.4
Input the password (the last 3 digits of your serial nu mber) using the number keys. Press ENTER when when done.
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CRC -15W Application Note 5132-5031 Rev. B
Well Detector Manual Re-Calibration
2.5
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2.4.5
Select RESET HV . The “HV DAC” screen appears.
2.4.6
Press 9(Y) to reset the HV. Input “128” using the number keys. Press ENTER when done. The screen “AUTOCAL MUST BE PERFORMED – ANY KEY TO CONTINUE” appears.
2.4.7
Press the ENTER , then the HOME keys.
Verify there are no sources in the area. Verify that power is applied to the printer (optional). Perform a BACKGROUND measurement by the following ke ystrokes: 2.5.1
Press the BKG key.
2.5.2
Press the ENTER key.
2.5.3
Press the COUNT key.
The unit will count for a period of 20 seconds. At the end of that time period, press the WELL key to accept and save this measurement. The printer will also print out the value of the background measurement. Counts for this measurement should be around 500-700 cpm. Note:
2.6
The background measurement will vary depending on the normal background of the area where the unit is located.
Place the Cs137 source into the detector well and perform a count using the following keystrokes: 2.6.1
Press the WELL key.
2.6.2
Press 1 to select WIPE .
2.6.3
Press 3 then 0 to input a count time of 30 seconds. Press the ENTER key.
2.6.4
Press the COUNT key.
At the end of the counting period, the unit will display the total counts. To display the bar graph, press the DSPLY key. To stop the counting at any time, simply press the COUNT key; to resume counting, press the COUNT key again.
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CRC -15W Application Note 5132-5031 Rev. B
Well Detector Manual Re-Calibration
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If most of the counts displayed are in either the lower or upper channel, then the High Voltage (HV) Adjustment Screw will need to be rotated a considerable amount. If this is the case, the detector may be defective and the HV Adjustment Screw may not bring the unit into calibration. If this happens, the unit will need to be sent to the factory for repair. 2.7
Compare the values of the counts in the appropriate channels. Calculate the ratio of the channels (see the Example below). The ratio should be .68 – .74. Counts in CH5 = 41.22 kcpm,n
EXAMPLE:
Counts in CH4 = 69.53 kcpm,n Counts in CH5 Counts in CH4
=
41.22 69.53
= 0.593
Turn the HV Adj. Screw clockwise
If the ratio is too high, turn the High Voltage (HV) Adjustment Screw counterclockwise. If it is too low, turn HV Adjustment Screw clockwise. Note:
Adjustment directions are referenced to looking at the rear of the detector.
After making an adjustment, perform another count and recalculate the ratio. Repeat this step until the ratio is within the specified range. 2.8
Once the ratio is within the required range, perform a BACKGROUND measurement by using the following keystrokes: 2.8.1
Press the WELL key.
2.8.2
Press the BKG key. Press ENTER .
2.8.3
Press 2 then 0 to input a count time of 20 seconds. Press the ENTER key.
2.8.4
Press the COUNT key.
At the end of the counting period, the unit will display the total counts. Press the ENTER key to accept this measurement. The printer will also print out the value of the background measurement. Counts for this measurement should be around 500-700 cpm. 2.9
Auto Cal is the next step. To perform Auto Cal, follow the steps below: 2.9.1
Press the WELL key.
2.9.2
Press the UTIL key.
2.9.3
Select AUTO CAL.
2.9.4
Place the Cs137 Standard Source into the well. Press ENTER .
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CRC -15W Application Note 5132-5031 Rev. B
Well Detector Manual Re-Calibration 2.9.5
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Press the COUNT key.
The unit will count for the set period of time and during this period it will be comparing the ratio and adjusting the internal DAC. The unit may perform this process 3-4 times as it compares and adjusts the high voltage. At the end of this period, the unit will print out the results. Verify the Gain Reference Number. This number should be between 118 and 138 for an acceptable range. If the Gain Reference Number is within limits, go on to step 2.9. If the setting is out of the limits, go back to step 2.4. 2.10
The next step is to measure the Conversion Factor. To measure the Activity CF, follow the steps below. 2.10.1
Press WELL, UTIL.
2.10.2
Select SETUP . Enter the PASSWORD (last 3 digits of Serial Number). Press ENTER .
2.10.3
Select CONV FACTORS .
2.10.4
Press NUCL. Press 2, 7, 1, 3, 7 for Cs137. Press ENTER . Answer NO to OK.
2.10.5
Select MEASURE CF .
2.10.6
Enter the Time, Date & Activity of the Test Source.
2.10.7
Verify source information. Answer YES to OK.
2.10.8
Insert the Cs137 into the well and press ENTER .
2.10.9
Press the COUNT key.
2.10.10 At the end of the counting period, verify that channels 4 and 5 are selected. Press ENTER . 2.10.11 Answer YES to OK. 2.10.12 Press the HOME key. 2.11
The next step is to determine the Calibration Factor. This is determined by the following steps: 2.11.1
Measure BKG.
2.11.2
Perform Auto Cal. Count for 60 sec. If the Energy Deviation is over 0.5%, perform Auto Cal once more. The Energy Deviation should be within 0.5%.
2.11.3
Measure BKG.
2.11.4
Press TEST to perform 3 Tests at 180 seconds each using the Cs137 Source.
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CRC -15W Application Note 5132-5031 Rev. B
Well Detector Manual Re-Calibration
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2.11.5
Print out the test results after each test (If no printer is attached, record the Energy Deviation on a piece of paper.). Verify that the Energy Deviation is less than ± 1% on each test.
2.11.6
Calculate the Activity Deviation Average by adding the activity deviations (not Energy Deviation) of the three tests and dividing by three.
2.11.7
Calculate the Calibration Factor: The Calibration Factor = (1 - Average Activity Deviation) i.e., (100.0 - Average Activity Deviation in %)/100.
EXAMPLE:
Test 1 Cs 137 Standard: 89.0 µCi Measured as: 88.0 µCi Deviation: -1.1%
Test 2 89.0 µCi 88.5 µCi -0.5%
Test 3 89.0 µCi 88.3 µCi -0.7%
Average Activity Deviation = (-1.1%) + (-0.5%) + (-0.7%)/3 = (-2.3%)/3 = -.77% System Calibration Factor = {100.0 - (-.77)}/100 = 100.77/100 1 = 1.0077 2.11.8
Press HOME until returned to the Chamber Measurement screen.
2.11.9
Press UTIL, 9, 5, SPC, 1, 3 and ENTER .
2.11.10 Select COUNTER. 2.11.11 Select CAL FACTOR. Press 6(N) to answer NO to CAL FACTOR. 2.11.12 Input the calculated Calibration Factor, press ENTER . 2.11.13 Confirm the entered Calibration Factor. 2.11.14 Press the HOME key. 2.12
1
Next, perform a TEST by the following steps: 2.12.1
Press the WELL key.
2.12.2
Press the TEST key.
2.12.3
Verify that the source is still in the well an d press the ENTER key.
When the measured results are less than the activity of the standard, the calibration factor is greater than one.
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CRC -15W Application Note 5132-5031 Rev. B
Well Detector Manual Re-Calibration 2.12.4
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Press the COUNT key.
After the count period, the unit will print out the test results. The energy deviation should be 0.0% ± 2.5. 2.13
The unit should now be calibrated.
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CRC -15W Application Note 5132-5031 Rev. B
Well Detector Manual Re-Calibration
ECO#
Date
Rev
AO1776
3/00
A
AO2161
10/02
B
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Dept. Rep. (Signature)
Q.C. (Signature)
G. Bargerstock
G. Bargerstock
