AMS has been measuring the in-service response time of process sensors in nuclear facilities since our inception in 1977. We perform these and other tests in essentially all of the 100 or more nuclear power plants in the United States and many in Europe and Asia.

The response time of temperature sensors is tested in-situ using the Loop Current Step Response (LCSR) method and Self-Heating Index (SHI) measurements. The LCSR method is based on heating the RTD’s sensing element with a small electric current. This current causes a temperature transient in the RTD that is then analyzed using AMS proprietary software to determine the RTD’s response time. The LCSR method has been formally approved by the U.S. Nuclear Regulatory Commission (NRC) for measurement of “in-service response times” of safety-system RTDs in nuclear power plants.

In addition to LCSR tests, SHI measurements are made on nuclear power plant RTDs as an added measure of dynamic performance. As in LCSR test, SHI measurements involve a series of small electric currents that are applied to the RTD to measure the increase in its resistance as a function of input electrical power. The result, referred to as the SHI, corresponds to the RTD’s ability to dissipate heat and is thereby related to its dynamic performance.

The response time of pressure, level, and flow sensors is measured using the noise analysis technique. This technique is based on monitoring the natural fluctuations (noise) that exist at the output of sensors while the plant is operating. The noise is extracted from the sensor output by removing the DC component of the signal and amplifying the AC component. The noise data is then analyzed in the frequency and/or time domain to provide the response time of the sensor. An extra advantage of the noise analysis technique is that it provides the response time of not only the sensor but also the sensing line that brings the pressure information from the process to the sensor. Any blockages, voids, or leaks in the sensing line manifest themselves in the noise data and in terms of an increase in the measured response time.

The LCSR test, SHI measurements, and noise analysis are all performed remotely from the control room area where the field leads from the sensors reach the process instrumentation cabinets. Performing these tests in-situ is advantageous because it provides the actual in-service response time of the sensor accounting for all installation and process condition effects on response time. The best time to perform these measurements is at normal operating pressure and temperature (NOP/NOT) during normal power operation or at hot standby conditions.

The calibration of temperature sensors in nuclear power plants is verified using the cross calibration technique and calibration of pressure, level, and flow sensors is verified using the online monitoring (OLM) method. The cross calibration and OLM methods can use data from the plant computer or from a stand-alone data acquisition system that is set up in the plant for the tests.

AMS not only provides sensor response time and calibration monitoring services, but also sells equipment and training services to the nuclear industry to enable the users to perform the tests in-house.