AMS provides equipment, procedures, and personnel to perform laboratory and field testing services. All AMS testing technologies are available on a service basis as well as through the purchase of AMS equipment, training, and support for those customers who are interested in performing the tests in-house. The results of work performed under a service contract are usually provided in a written report and the supporting material is maintained at AMS for audits, reviews, and for reference purposes.
RTD Response Time Testing Services
The response time of an installed RTD is measured using the Loop Current Step Response (LCSR) method. This method is based on heating the RTD's sensing element with a small electric current (usually about 35 to 80 milliamperes) applied to the RTD's extension leads. The current causes a temperature transient in the RTD that can be analyzed to give the RTD's response time.
The advantage of the LCSR method is that it permits remote testing of an RTD as installed in an operating process, and thereby provides the actual "in-service" response time of the RTD. The test accounts for all installation and process condition effects on RTD response time.
The procedure for in-plant testing of RTDs using the LCSR method involves the following general steps:
- Setup the LCSR test equipment near the cabinets where the RTD field leads reach their signal conversion/conditioning equipment in the plant instrumentation cabinets
- Select the RTD(s) to be tested and record the RTD tag number and other information on a test data sheet. Up to five RTDs can be tested simultaneously using the AMS multichannel RTD response time test equipment
- Put the RTD channel in test for the duration of LCSR test (usually 15 to 30 minutes).
- Disconnect the RTD's field leads in the plant instrumentation cabinet
- Connect the RTD's leads to the LCSR test equipment
- Perform the LCSR test. Repeat the test 10 to 30 times depending on the level of process noise on the data
- Store the data on computer disks
- Disconnect the RTD(s) from the test equipment and connect it back to the plant equipment
- Return the RTD(s) to service
- Repeat this procedure for the next RTD or set of RTDs.
The actual in-plant tests are performed according to a detailed step-by-step procedure.
Upon receipt of a service contract, AMS will send copies of the pertinent test procedure(s) to the customer for review and approval, or to be incorporated into a plant procedure format, if necessary. In some plants, AMS procedures are used as they are, and in other plants, the procedures are converted into the plant procedure format or a new plant procedure is written, incorporating the AMS procedures. AMS will work with the customer as necessary to complete the procedure(s) and review the final draft. AMS will then ask the customer to provide a tentative schedule for the test and will maintain telephone contact with the customer to firm up the schedule as the test date approaches.
RTD Cross Calibration Services
Cross calibration is a test for consistency of a group of RTDs to ensure that accurate steady state temperature measurements are provided to the plant control and safety systems. The test involves a systematic intercomparison of readings of the RTDs to identify the ones that may have a larger-than-normal deviation from the average reading of all the RTDs.
In performing cross calibration, the resistance of all RTDs are measured sequentially and converted to equivalent temperatures using the most recent calibration tables available for the RTDs. The resulting temperatures are then averaged and the temperature deviation of each RTD from the average is calculated. Any RTD that exceeds a pre-specified temperature deviation is flagged and/or removed from the average and the process is repeated as necessary to identify the outliers (if any). Sometimes, instead of RTD resistance, the temperature readings of the RTDs are used for the cross calibration test.
Cross calibration tests can be performed at one or more temperature plateaus at isothermal conditions when the reactor coolant hot leg and cold temperatures are at approximately the same temperature. The test can also be performed when the temperature is increasing or decreasing monotonically at a reasonably constant rate. This approach is referred to as dynamic cross calibration or ramp cross calibration. The advantage of this approach is that it does not require the plant to maintain constant temperature and therefore saves on critical path time.
If cross calibration data is collected at three or more reasonably spaced temperature points during plant heat up or cool down, then a new calibration table can be generated for an outlier RTD using the cross calibration data. This will save substantial time and cost as it will help prevent RTD replacement.
Precision Laboratory Calibration of RTDs
AMS provides laboratory and field calibration services for industrial RTDs. The work is done in a fully computerized and modern facility that is equipped with high temperature RTD calibration and annealing furnaces, state-of-the-art oil bath and ice bath equipment, Standard Platinum Resistance Thermometers (SPRTs) with direct traceability to NIST, and triple point cell equipment for maintaining temperature standards in-house.
RTD Cross Calibration Under Temperature Ramp Conditions
AMS has developed and validated a new software for analysis of dynamic RTD cross calibration. With dynamic RTD Cross Calibration, data may be collected during cool down at the end of a cycle at shutdown or during heat up at the beginning of a cycle during start up. The test time or critical path time is substantially reduced with dynamic cross calibration as the plant does not have to hold at temperature plateaus. Furthermore, if data is collected at three or more reasonably spaced temperature points, the cross calibration data can be used to generate a new calibration table for an outlier. That is, an outlier RTD does not have to be replaced in most cases. This saves substantial costs that are normally involved to replace an RTD, especially if the outlier is identified at startup which would normally require the plant to cool down to replace the RTD. |
