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Howto Measure RTD over long distances




1. Introduction

The RTDs are the most expensive, but they also provide best accuracy and best resolution for the measurement. This, however, only if appropriate analogue circuitry will be used (which of course will add cost to the already high price of the sensor itself). The appropriate analogue circuitry constitutes the subject of this article. RTDs are regarded as the best quality temperature sensors (when it is worth paying for them). They provide accurate and stable measurements over time, and, most important, they provide a linear resistance-temperature characteristic. In the figure 1 is shown the resistance-temperature characteristic of the most common RTD, the PT100, which gives 100Ohms at a temperature of 0 Celsius degrees.

howto-measure-rtd-over-long-distances

2. Features and design

RTDs also represent a continuously expanding technology, better materials being researched and used, further improving the characteristics of the sensors. The purpose of the analog circuitry buffering the sensor is to transform the resistance variation of the sensor in a variation of voltage which can easily be converted in digital values by an ADC. Although there are several methods to do this, the most common one is to build an analogue precision constant current source that will force a known and constant current through the RTD. The variation of the voltage will linearly depend on the variation of the sensor resistance, and thus on the temperature.

1. Introduction

The RTDs are the most expensive, but they also provide best accuracy and best resolution for the measurement. This, however, only if appropriate analogue circuitry will be used (which of course will add cost to the already high price of the sensor itself). The appropriate analogue circuitry constitutes the subject of this article. RTDs are regarded as the best quality temperature sensors (when it is worth paying for them). They provide accurate and stable measurements over time, and, most important, they provide a linear resistance-temperature characteristic. In the figure 1 is shown the resistance-temperature characteristic of the most common RTD, the PT100, which gives 100Ohms at a temperature of 0 Celsius degrees.

For more detail: Howto Measure RTD over long distances

 

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