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AMS provides equipment, services, and training to enable plants to perform on-line monitoring as a means of verifying the calibration of pressure, level, and flow transmitters, thereby reducing the frequency of manual calibrations for these sensors.
Test Principle
 Traditional instrument calibrations absorb substantial manpower to isolate the sensor, calibrate it, and return it back to service. The calibration effort typically involves two steps:
- Identify if the calibration is needed
- Calibrate if needed
The first step can be automated by on-line monitoring. AMS provides on-line monitoring equipment and services to identify if an instrument has lost its calibration. This will allow plants to limit their instrument calibration effort to only those instruments which need calibration, as opposed to the current practice which typically calls for periodic calibration of most instruments.
Although on-line calibration monitoring is applicable to most instruments, including both the sensor and the rest of the instrument channel, the main benefit is in extending the calibration intervals of pressure, level, and flow transmitters. It is for this reason that AMS has focused its on-line monitoring program mainly on the calibration reduction application.
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NRC Approval
 In July 2000, the U.S. Nuclear Regulatory Commission (NRC) issued a Safety Evaluation Report (SER) approving the on-line monitoring approach for extending the calibration interval of safety related pressure, level, and flow transmitters in nuclear power plants. With this approval, nuclear power plants are allowed to extend the calibration interval of their pressure, level, and flow transmitters up to eight years.
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Payback
On-line calibration monitoring reduces the personnel workload and radiation exposure, especially during plant outages, and protects the instruments from accidental damage during manual calibrations.
The economical benefit of the approach depends on the number of instruments that are included in the on-line calibration monitoring program. The greater the number of instruments included, the more benefits are realized. Typically, if 100 or more transmitters are included in the on-line calibration monitoring process, the entire cost of program implementation can be recovered in a single fuel cycle.
Condition Monitoring
In addition to safety related transmitters, the on-line calibration monitoring can obviously be used to verify the calibration of non-safety related transmitters and to perform equipment and plant condition monitoring.
For condition monitoring, the reading of an instrument for a given process parameter is compared with an estimate of the process parameter and the deviation between the two is tracked within a predetermined threshold. If the threshold is exceeded, an alarm/alert/action request is issued.
The process estimate for condition monitoring is determined by averaging the readings redundant instruments and/or modeling the outputs of non-redundant instruments. Both empirical and physical modeling may be used for process estimation.
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AMS Products for On-Line Monitoring
AMS provides a number of products to help plants implement on-line monitoring for calibration reduction, condition monitoring, or a combination of the two. This includes a feasibility demonstration to document the validity of the on-line monitoring approach for the plant. In doing so, on-line monitoring results are compared with manual calibration results for one or more cycles to ensure that on-line monitoring will not miss a transmitter that has lost its calibration. Once the validity of this approach is established, on-line monitoring is implemented through one of two alternatives: (1) a service arrangement whereby AMS performs the work for the plant (2) a technology transfer arrangement whereby AMS provides the plant with independent capability to perform the work.
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