PT1000 temperature probe: Our buying advice
Choice of PT1000 probe and instructions for use
A PT1000 element consists of a coil of wire or a deposited film of pure metal. The resistance of the element increases with temperature in a known and repeatable manner. The Pt1000s exhibit excellent accuracy over a wide temperature range.
- Temperature range: -200 to 700ºC
- Sensitivity: the voltage drop across an RTD provides a much larger output than a thermocouple.
- Linearity: Platinum and copper RTDs produce a more linear response than thermocouples or thermistors. RTD nonlinearities can be corrected through the proper design of resistive bridge networks.
The most commonly used material is platinum with a resistance of 1000 ohms at 0ºC and a temperature coefficient (Alpha) of 0,0385 ohms / ºC.
Other elementary materials also used are the copper, nickel et nickel-iron. The elements of platinum predominate because of their wider range, and because platinum is the most repeatable and stable of all metals.
Tolerance of PT1000; (Alpha = 0.003850 @ 0ºC)
|CLASS B||± 0,30ºC|
|CLASS A||± 0.15ºC|
|1/3 B (1/3 DIN)||± 0,10ºC|
|1/10 B (1/10 DIN)||± 0.03ºC|
The linearization equation of a PT1000 probe:
Connection / Wiring details:
Different types of connection. Standard color code; A is white, B is red.
|2 Wires: Basic connection where the conductor is short. No compensation wire.||3 Wires: The most common with 3 connection wires, the instrument measures the resistance of wire B and deduces it from its measurement.||4 Wire: The 4 wire connection is the most accurate measurement. The instrument measures the resistance of the four conducting wires and deduces it from its measurement.||Double Pt1000: 3-wire double RTD connection with two different sensitive elements.|
No maintenance is required for RTD sensors, however, scheduled ice point (0ºC) calibration checks are recommended.
Method for determining the resistance to the ice point (0 ° C)
Prepare an insulated container at least 300 mm deep and with an internal diameter of 100 mm.
PROCEDURE. The procedure should be as follows:
a) Fill the insulated container with finely divided ice made from distilled water.
Note: If the chilled water of distilled water is not available, the transparent part of a block of commercial ice will suffice, provided that all surfaces are first washed with distilled water.
b) Mix ice with water distilled previously cooled using the stirrer, then drain the excess water. The ice should be glassy but there should be no free water left.
c) Connect the thermometer to a measuring device resistance and adjust so that the electrical power dissipated in the element does not exceed 1 m W.
d) Immerse the thermometer in ice so that the element is at a depth of at least less 150 mm. Make sure the bottom of the thermometer is at at least 30 mm from the bottom of the container. Note: Thermometers with stem lengths less than 150mm should be submerged to their maximum possible depth.
e) When the element reaches equilibrium with the ice, action can be taken. Measurements made with direct current should be made with current in both forward and reverse directions. Note: The time it takes for the element to reach equilibrium is normally about 3 minutes.
f) Decrease the immersion depth of the element by 50 mm or 20% of the length of the rod, the smaller of the two.
g) Repeat step (e). If the reading change is more than one-third of the appropriate tolerance, the whole procedure should be repeated with fresh ice.
Precision: RTD Pt1000 sensors; at 0 ºC = Class B +/- 0,3 ºC, Class A +/- 0,15 ºC, 1/10 DIN = +/- 0,03 ºC
Risk of self-heating
The current through the sensor will cause heating: for example, a detection current of 1 mA through a 1000 ohm resistor will generate 1 mW heat. If the sensor element fails to dissipate this heat, it will signal a artificially high temperature. This effect can be reduced either by using a large sensor element or by ensuring that it is in thermal contact with its surroundings.
The use of a detection current of 1 mA will give a signal of only 1V. Because the change in resistance for one degree Celsius is very small, even a small error in measuring the voltage across the sensor will produce a large error in measuring the temperature. For example, a voltage measurement error of 1mV will give an error of 0,4 ° C in the temperature reading. Likewise, a 10 μA error in the detection current will give a temperature error of 0,4 ° C.
Due to the low signal levels, it is important to keep cables away from electrical cables, motors, equipment and other devices that may emit electrical noise. Using a shielded cable with the screen grounded at one end can help reduce interference. When using long cables, it is necessary to verify that the measuring equipment is able to withstand the resistance of the cables.
More information on the values of the Pt1000 probes below!
|Precision class||R / T conversion table|