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Bondable Resistance Temperature Sensors and Associated Circuitry

LST Matching Networks

Commercial single- or multiple-channel strain indicators are excellent readout devices for TG temperature sensors , and are particularly convenient when combinations of strain and temperature are to be measured or recorded simultaneously. This readout method requires the use of an interface signal conditioning network, referred to as an LST network , to "match" the temperature sensor response to that of the strain indicator. The arrangement is shown below.



LST network circuit.

The LST network is a small, completely encapsulated unit consisting of four special precision resistors. When used with standard 50-ohm nickel TG temperature sensors, it performs the following three functions:
  1. Provides a linear resistance change at the output terminals.
     
  2. Attenuates the resistance change slope to the equivalent of 10 or 100 /° for a gage factor setting of 2.00 on the strain indicator. It is usually most practical to use 10 /° networks when a large temperature range is involved, and 100 /° networks for high resolution of small temperature spans.
     
  3. Presents a complete 350-ohm half-bridge circuit to the strain indicator.
Differential temperature measurements can be made by combining two TG sensors and two LST networks. The arrangement shown below provides a half-bridge circuit to the strain indicator in which the ACTIVE arm responds to sensor 1, and the DUMMY arm to sensor 2.


An alternate method is to arrange the networks to form a full-bridge circuit as shown below, which may be preferred for some types of readout equipment.


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