Both sensors have the same temperature function and follow the following table; The Pt1000 values are simply a factor 10 higher. Note: see table under: Resistance value of Pt 100 sensor at various temperatures. The difference with Pt100 is that the value varies only 0.391 Ω per ºC. If we connect the Pt100 with a pH cable of 10 m then the resistance of this cable will be 0.7 to 0.8 Ω which results in a +2 ºC measuring error on the temperature signal. If we connect a Pt1000 sensor, then the sensitivity is 3.91 Ω/ºC. So when connected to the same cable the measuring error is only +0.2 ºC. Good enough for pH measurement.

DESCRIPTION

Pt100 is the common abbreviation for the most common type of resistance temperature sensor used in industry.

It has a specified resistance of 100.00 ohms at 0°C and is made of Platinum which has an accurately defined resistance vs. temperature characteristic.

There are two minor variations, the most common giving 138.50 ohms at 100°C (DIN standard) and the other giving 139.00 ohms at 100°C (popular in Japan). It is most important to know which you are using when ordering or calibrating instrumentation.

Because accurate tables of resistance v. temperature are available it is common practice to calibrate instruments using precision decade boxes from table values.

Pt100 sensors were originally made with platinum wire wound on a ceramic former but are now made more cheaply by depositing a platinum film onto a ceramic substrate.

Typical accuracies are 0.2%, 0.1% and 0.05% of value at 0°C. The higher the accuracy the higher the price.

Note that there are two error characteristics, an offset error (ie. how far out it is at 0°C) and a span or gain error (ie. how the resistance change with tempearture agrees with the theoretical figure). The gain error depends on the offset error and the impurities in the platinum.

These sensors are also made in 200, 500, and 1000 ohms values.

Although the sensors are sold loose, it is usual to buy them made up into stainless steel probes for insertion into processes.

Pt100 elements are specified over a temperature range of -200°C to 850°C however the actual operating temperature is determined by the construction of the probe into which they are incorporated. Typical low cost probes are made by soldering the Pt100 to PVC or silicon insulated copper wires. Obviously these are limited by the maximum temperature of the insulation. For higher temperature work the Pt100 is silver soldered or crimped onto mineral insulated wires and embedded in an insulating medium such as aluminium oxide powder.

At higher temperatures the platinum film can slowly evaporate which permanently changes the resistance of the sensor.

COMPARISON OF SENSORS