Temperature sensing devices, such as RTDs and thermocouples, provide necessary temperature indications for the safe and continued operation of the DOE facility fluid systems. These temperature indications may include:

Reactor hot and cold leg temperatures Pressurizer temperature

Purification demineralizer inlet temperature Cooling water to and from various components Secondary feed temperature

EO1.6STATE the three basic functions of temperature detectors.

EO 1.7 DESCRIBE the two alternate methods of determining temperature when the normal temperature sensing devices are inoperable.

EO 1.8 STATE the two environmental concerns which can affect the accuracy and reliability of temperature detection instrumentation.

Functions of Temperature Detectors

Although the temperatures that are monitored vary slightly depending on the details of facility design, temperature detectors are used to provide three basic functions: indication, alarm, and control. The temperatures monitored may normally be displayed in a central location, such as a control room, and may have audible and visual alarms associated with them when specified preset limits are exceeded. These temperatures may have control functions associated with them so that equipment is started or stopped to support a given temperature condition or so that a protective action occurs.

Detector Problems

In the event that key temperature sensing instruments become inoperative, there are several alternate methods that may be used. Some applications utilize installed spare temperature detectors or dual-element RTDs. The dual-element RTD has two sensing elements of which only one is normally connected. If the operating element becomes faulty, the second element may be used to provide temperature indication. If an installed spare is not utilized, a contact pyrometer (portable thermocouple) may be used to obtain temperature readings on those pieces of equipment or systems that are accessible.

If the malfunction is in the circuitry and the detector itself is still functional, it may be possible to obtain temperatures by connecting an external bridge circuit to the detector. Resistance readings may then be taken and a corresponding temperature obtained from the detector calibration curves.