Flexible Temperature Measurement with the ZSSC3241 Enables Bridge as Temperature Sensor

Accurate measurement using sensor elements requires precise and local measurement of the element’s temperature for correction and compensation across a wide operating range. Thus, an integral part of Sensor Signal Conditioner (SSC) functionality is to provide at least one or more methods to measure temperature of the sensor element, which is typically a resistive bridge or capacitive transducer.

One simple and effective way to create a precise thermometer is to build a standard circuit called a PTAT (Proportional To Absolute Temperature) that generates a linear, consistent voltage versus temperature. This is fine as long as the SSC silicon is tightly coupled thermally to the sensor element such that the temperature of the two elements is nearly equal. In some cases, however, the sensor element may be separated from the SSC by several centimeters or even further. In these instances, the SSC cannot be used predictably for temperature compensation and some type of external thermometer is needed that can be co-located with the bridge sensor. Silicon diodes or thermistors of the NTC or PTC type are commonly used for these cases, but these solutions require additional components and may have the same issue of co-location with the primary sensing element. For resistive bridges, the ultimate way to measure the sensor temperature accurately with no additional cost or space is to use the temperature coefficient of the bridge itself. However, this requires some additional complexity in the biasing circuitry for the sensor bridge and more sophisticated calibration algorithms in the SSC to linearize the temperature coefficient of the bridge, which may exhibit up to third order variation. With advanced modern SSCs like the ZSSC3241, this functionality is fully integrated and supported. The ZSSC3241 can support temperature measurement using an internal PTAT, external diodes or thermistors, and using the main sensing bridge itself as the thermometer. The various options are fully programmable and configurable using internal Non-Volatile Memory (NVM) for optimal performance based on system requirements.

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