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PT 100 4 wire sensor

Hi everyone,

my name is John and i am a student at the technical university of Patras, Greece. I could really use some help here, with this RTD "PT 100" temperature sensor. I have developed a temperature data acquisition system using a card, connected to my PC serial port. I have tested it by using a LM 35 (requires Vcc = 5V) temperature sensor and it works. The thing is that i want to adjust a PT 100 temperature sensor. I bought one but...

The PT 100 has 4 wires (2 white, 2 Red), i have tried using my multimeter to measure the output but it doesn'y work (PT 100 ouput 1mV/Celsium). If i connect it to my card then i get 0 input. Does anyone has any idea or experience about PT 100 temperature sensors.

Thanks in advance

Reply to
John Tzoutzakis
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A PT100 probe does not generate voltage. At 0 deg Celsius, the resistance of the RT (resistance thermometer) should be 100 ohms. At 100 deg Celsius, the resistance should be 138.5 ohms. It has 4 wires for a system which incorporates long cable runs which, as the cable already has a resistance and the resistance varies with heat, the measuring device can compensate using this. You should find the two red wires are shorted in the head of the thermometer on one side of the RT and the two white shorted on the other. I have only worked on the 3 wire RT system which is just as effective on long cable runs, although all our measurement gear is pre built. One way of overcoming your problem would to be to put the RT into a 741 op amp circuit (being careful not to overload the RT), to drive the PC card. Hope this helps, PF

Reply to
Paul

ok, Ill try this one,,,

PT100 is the type of sensor, PT means 'Platinum' whos resistance at 0C is

100 Ohms. The resistance of the PT100 changes by around 0.38ohm[Europe] or 0.39ohm[US] / deg C

A 4 wire PT100 gives two wires back from the resistance in order to measure the resistance of the cable used.

There are several coverters avaliable to change PT100 to 4-20ma/0-10v/0-5v etc.

Hope this is of some help.

sQuick....

Reply to
sQuick

Platinum sensors are resistive devices. With a 4-wire sensor, you put a small current through one red & one white wire. The voltage between the other red & white wires is proportional to the resistance of the sensor. You need to keep the current low enough to prevent self heating of the sensor.

You can also use the 4-wire sensor in a 3-wire bridge configuration. Do a Google search and you will find a lot more information.

Ben Miller

Reply to
Ben Miller

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