Troubleshooting Thermo Scientific LevelPRO Gauges

Transcription

1 Troubleshooting Thermo Scientific LevelPRO Gauges Key Words Scintillation detector Current board Relay output Communications Level indication Purpose A chapter in the user guide for the Thermo Scientific LevelPRO gauge is dedicated to troubleshooting. Providing the material from that chapter in this stand-alone document will help users keep troubleshooting procedures easily accessible. Note: This technical bulletin is to be used as a quick reference for troubleshooting the LevelPRO gauge. It is not meant to be used as a replacement for the installation and user guides. Note: Troubleshooting must be done only by qualified personnel. Note: Do not use the HART communication system for troubleshooting. You must use either the Thermo Scientific Model 9734 Handheld Terminal (HHT) or a computer with RS232/RS485 converter and the Thermo Scientific TMTComm communication software to access the technical troubleshooting capabilities of the LevelPRO system. The LevelPRO system is ESD sensitive. Use proper ESD protective equipment and procedures. Failure to comply with ESD procedures can result in circuit damage. The Scintillation Detector Note: Enable the Service Only Items in the Special Functions menu before proceeding with this section. If you suspect a problem with the scintillation detector, you can check the detector output by accessing the Internal Value of Sensor Signal item in the Snapshot item of the Diagnostics menu. The direct access code (DAC) for this item is If the tank is at least partially empty, this value is the count rate in counts/second (cps) and should be much larger with the source shutter on than with the shutter off (typically more than ten times larger). As a further check, empty the tank and compare the Internal Value of Sensor Signal item to the STD Value in Use item, which is displayed in the Sensor Standardization menu. The DAC for this item is If the gauge was working properly when it was last standardized, the two values should be similar. The match will not be exact because the STD value is filtered and corrected for background radiation and source decay. If the displayed signal value is not behaving correctly, check the gauge head for misalignment, buildup, or wear, and check for debris in the beam path and faulty shutter operation before testing the detector signals. Use a long handled brush to remove debris in the beam path to ensure that no part of your body, including your hands, enters the radiation beam path.

2 If you can eliminate these other factors, it is likely that the cause is related to the CPU board. Verify that the cable connections between the detector board and CPU board are securely seated. If the problem persists, contact Thermo Fisher Scientific Technical Support. 1. Locate the J11 connector on the CPU board. The blow-away jumper setting for normal operation is shown in Figure 1. Remove all power from the unit prior to opening the enclosure. Electrocution can result if power is present. The Current Board If you suspect a problem with the current output, attach an ammeter in series with the current output load and verify the current output at various levels. Use the commands from the User Service & Related Items submenu within the Security, Service, and Diagnostic Functions menu group to hold the current output at specific levels for testing. Figure 1. Blow-away jumper in normal operation position 2. With power removed, remove the blow-away jumper, rotate it 90 clockwise, and insert it onto the pins as shown in Figure 2. The Relay If you suspect a problem with a relay output, attach a continuity tester to the suspected relay output and use the Test Relays commands in the Factory Service & Related Items menu to test relay operation. Communication Problems If the gauge will not communicate at all, try hard booting the system. Note: This procedure will erase memory and return all parameters to the factory defaults. Remove power from the gauge prior to performing this procedure. Figure 2. Blow-away jumper in erase memory position 3. Apply power to the gauge for approximately 30 seconds. 4. Remove power from the gauge, and return the jumper to its original position. 5. Apply power to the gauge. All parameters will be set to factory defaults.

3 Level Indication If the gauge indication is 100% and will not change, review this section carefully and then follow the steps provided. Equipment Required For this procedure, you will need: One Model 9734 HHT or a PC with RS232/RS485 converter and TMTComm software installed One multimeter Site Preparation You will need to access the gauge while it is in the housing and in the radiation field coming from the radioactive source on the opposite side of the vessel. The source shutter will need to be ON and the level in the vessel should be as low as possible, without adversely affecting the process. If you cannot lower the level of the process material in the tank to a point well below the top of the detector sensitive length you may not be able to perform all the required tests. If you are in a classified area, a HOT WORK permit may be necessary. Procedure the transition from the empty radiation levels to the lower radiation levels where the beam is being blocked by the remaining material in the vessel. If you have access to the original survey document completed when the gauge was installed, you will also be able to verify whether there is any significant reduction in radiation field readings that cannot be accounted for by normal source decay. This may indicate a problem with a buildup of process material on the vessel walls. If a radiation survey meter is not available or it is not feasible to visually confirm the material level in the vessel, the indication of the vessel level must be accepted. 3. Connect to the LevelPRO detector. If you have to remove the detector housing lid to connect the communication device to the gauge, verify that the red power LED on the CPU board is lit (see Figure 3). The LED indicates that the CPU is getting the 5 Vdc required for operation. If the gauge is powered by 120 Vac, this voltage will be present while accessing the gauge. Proceed with caution. Do not come in contact with this voltage. 1. Verify that the radioactive source shutter is in the ON position. 2. Verify that the vessel is not actually full of material. Figure 3. Power LED on the CPU board If the system is AC powered and the LED is not lit, check the fuse on the power supply board (Figure 4), which is a amp sloblow. If the system is DC powered and the LED is not lit, check the F1 fuse located on the CPU board (Figure 5). If a radiation survey meter is available, use it to find the actual level. Do this by placing the survey meter detector between the vessel and detector. Starting at the top of the gauge measurement area, move the probe slowly down the length of the detector until you see

4 If the sensor signal does not change or is zero when you cycle the source shutter, the detector signal is getting lost or corrupted somewhere between the scintillation crystal and the CPU. The problem may be related to the photomultilplier tube (PMT), the triangle board (p/n ), the cabling (p/n ), or the CPU (p/n ). Figure amp slo-blow fuse on AC powered systems 5. The next step is to turn on the diagnostic measurements feature. Use DAC Press the right arrow once to change the selection from Do not enable (Figure 7) to Do enable (Figure 8) to enable diagnostic measurements and then exit. Do not enable diag measurements Change to Do Continue as is. Figure 7. Diagnostics measurements disabled Figure 5. F1 fuse on CPU board for DC powered systems 4. Using DAC , bring up the Internal Value of Sensor Signal item. Depending on application, source size, vessel wall, etc., the count rate should be in the thousands. The value shown in Figure 6 is for example only. Internal value of sensor signal 2.057E4 Figure 6. Example internal value of sensor signal Do enable diag measurements Change to Do not Continue as is. Figure 8. Diagnostic measurements enabled If the measurements do not show up on the screen, enter command 72, and they will appear. With the diagnostic measurements turned on, the display will toggle between two screens (Figures 9 and 10). Along with the level reading, four new values are displayed. These values are explained in the next section. While the detector value is still displayed, close the shutter on the radioactive source. The displayed count rate should go down towards zero. Open the source shutter and the count rate should go back up to where you started. If this occurs, the detector is working properly. The problem may be programming related % 0000 ERRSIG 1081 REF (cps) For setup, press Figure 9. Diagnostics measurement screen % 9175 VD 2215 CTLSIG For setup, press Figure 10. Diagnostic measurement screen 2

5 Diagnostic Measurement Values In addition to the level reading, four values are displayed on the diagnostic measurement screens. ERRSIG: This value may also be shown as HVCorr, depending on the version of software in the instrument. ERRSIG is a relative value representing the length of the control pulses for high voltage control. This number should be at or near 0. If it is staying under 10, the detector is under normal control and working correctly. If this number is running from 10 to 50, the detector may be damaged (often from being exposed to temperatures over 140 F for some period of time), and its indication should be suspect. If this number is running from 50 to 256 (the highest possible value), the gauge cannot control the high voltage. It is likely that the detector has failed. CTLSIG: This value may also be shown as HVCtrl, depending on the version of software in the instrument. This is a relative value representing the amount of control time the CPU is using to control the detector. The value can be from 10 to The normal control range for a new detector is from 2000 to Every detector will have a different value, but the value should always be steady. If the value is ramping up or down, then the detector is faulty and not under control. REF(cps): This value is the REF count rate in cps. It should be 1/8 of the VD count rate. The CPU will adjust the CTLSIG until the VD gets to 8 times the REF count rate. If it is unable to reach this 8:1 ratio, the CTLSIG will ramp up to 8000, go back to 10, and ramp up again. If the REF(cps) is a low number like 5, the reference counts are getting lost somewhere between the PMT and the CPU. Recorded Values The values listed in Table 1 are useful to Thermo Fisher Scientific Technical Support when troubleshooting the LevelPRO system. Please have these values readily available when calling for assistance. To recall these values, press EXIT, enter the DAC, and press the down arrow. Record the value shown. Press EXIT again to return to the main screen. The first four values {ERRSIG through REF(cps)} were accessed in step 5 of the above procedure. VD: This value is the DATA count rate in cps. It should be the same value as the internal value of the sensor signal (DAC ) recalled in step 4 of this procedure. If this value is above 9999, the display will show >9999. To display this value, you will need to enable the R&D test items by entering DAC The value will display in scientific notation. Be aware that other values will also change to scientific notation and lose their names. Therefore, it may not be desirable to leave this feature enabled very long. This value should increase with a lower process level and decrease with a raised process level.

6 Table 1. Recorded values for troubleshooting Parameter Name/DAC Description Value ERRSIG Error from stable control CTLSIG Control signal from CPU VD Data count rate REF(cps) Reference count rate Standardization (zero) value Snapshot of detector signal Software version Time constant in seconds Weeks since standardization Source half-life In addition to these offices, Thermo Fisher Scientific maintains a network of representative organizations throughout the world. Canada +1 (905) (905) fax China +86 (10) (10) fax India +91 (20) (20) fax United Kingdom +44 (0) (0) fax United States +1 (800) (713) (713) fax HART is a registered trademark of the HART Communication Foundation Thermo Fisher Scientific Inc. All rights reserved. Specifications, terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details.