PT 100 SIGNAL TREATMENT

[adri_dal]

Good to all, I have the programming of a v700 with snap snap i / o v200-18-e3 / 4 xb, one of the variables to control is the temperature of a liquid.

My first doubt is that if at pt100 input I can connect a ptc sensor with 2 wires instead of a pt100 probe with three or 4 wires as it comes in the connection scheme of the snap module.

The next one is if it is necessary to perform some linearization with that input value of the pt100 or already directly obtain that value in the variable my belonging to that input.

Greetings and thanks from anteman

[Joe Tauser]

I'm guessing when you say "a PTC sensor with 2 wires" you are talking about a thermistor.

The PT100 input is designed for a 100 ohm DIN RTD - 100 ohms at 0 degrees C, 0.385 ohms/deg C.

You'd actually have better luck designing a circuit to provide a voltage or current output based on the specifications of your sensor and the temperature range you are interested in.

Joe T.

[Isakovic]

Also, you don't need linearization. RTD inputs measure temperature directly, register will have a value of temperature x10 (102 C is 10.2 C).

[V700]

I also have V700 with snap i /o  v200-18-e3 / 4 xb

 i connect a 3-wire PT-100  and place the input in MI operand (C),   the value i get is about 5370.   I measure the resistance from the PT-100 to 120 Ohms so according to pt-100 table it has to be about 50C(the temperature in my room is 22C,maybe the sensor is not good).
I divide 5370 with 100(no 10 as mentioned in the last post) so i get 53C. Is that correct?

 

[Flex727]

Do you have the jumpers set correctly on your V200-18-E3XB module?

[V700]

Yes. I connect it to analog input 0

5A    4A    3B

[Joe Tauser]

Something is wrong with your sensor or your wiring.

The returned value is the temperature with one implied decimal, so your 5370 value is 537.0 C.  Definitely not right.

Do you have a make an model of the sensor, or at least a picture of the connection?

I'd check two things.  

1.  The wiring shows one side of the sensor resistor going to the CM terminal, not the ACM terminal.  This will be the odd-colored wire.  The two matching wires go to the two PT terminals.

2.  You measured the resistance and it was not what you expected, which is a good sanity check.   To further check your sensor type, fill a cup with ice cubes and then water.  Put the sensor in and let it stabilize - you should get very close to 100 ohms.

Joe T.

[V700]

My connection was wrong...

i tested with ice-cubes and it was close to 103 ohms.

thank you for helping!