Temperature is one of the most important parameters needing monitoring in the power system. For example, as an expensive and critical component of a power system, a large of number of transformers have been deployed on the transmission and distribution power grids. Due to long lead times for repair and replacement, temperature-based protection can limit the damage to a faulted transformer by identifying operating conditions. Along with smart grid migration, the industry demands accurate, repeatable, and reliable measurement of temperature, which can have a significant impact on the grid infrastructure cost, quality, efficiency and safety.
There are different ways to measure temperature based upon the type of sensor adopted, such as thermistor, thermocouple, and resistance temperature detector (RTD). The focus of this design is to measure temperature using RTD, a sensing element whose resistance changes with the temperature. The relationship between the resistance and temperature of an RTD is highly predictable, which allows accurate and repeatable temperature measurement over a wide range.
RTD requires constant current source for its excitation to produce a voltage output proportional to the resistance of the RTD. The resulting voltage output is measured by the analog-to-digital converter (ADC). In this design, there are a couple of nice things I want to share with you:
- With the same hardware, this design is carefully developed to support different lead wire configuration, such as 2-wire RTD, 3-wire RTD or 4-wire RTD
- Higher resolution ADCs with PGA (Programmable Gain Amplifier), which match current source and radiometric measurement techniques, are used to improve accuracy
- Furthermore, to minimize the noise impact on accuracy, which can be found in excitation source, and ADC reference voltage drift, a ratio metric approach is considered in this design along with a selected low-tolerance, low drift reference resistor
- Finally, this design coupled with an MCU board shows < ±2°C accuracy over wide range without calibration
For more details, check out the reference design here. (TIDA-00110)
