# Multisim and Ultiboard

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## RTD simulation Help

I am trying to use a VOLTAGE_CONTROLED_RESISTOR_VIRTUAL to simulate an RTD. From what I have read this is one way to simulate an RTD. I am using the voltage input as a simulation for temperature.

I want the value of my resistor to be 279.40 ohms @ 103.12 degreec C (or volts in this case).

I set the voltage supply to my VCR to 103.12V and the resistance value to 2.70946 ohms/volt

Am I missing something? What am I doing wrong?

Thank you,

Eric

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## Re: RTD simulation Help

Hi Eric,

I duplicated your circuit and there are two things you need to do get the right measurement:

- Reverse the polarity of the biasing battery, so the positive of the 103.12 battery to the positive of the voltage controlled resistor (VCR) and same for the negative end.

- When measuring the resistance of a VCR, it is better to measure the voltage accross and divide it by the current passing by because of the way the Ohmmeter device works (it adds a sample resistor in shunt and that will be affected by the controling voltage too). Another way is to run a DC operating point analysis and calculate this expression (V(1)-V(2))/I(R1).

I attached the design here.

Please let me know if you have other questions.

Mahmoud W

National Instruments

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## Re: RTD simulation Help

Greetings I am trying to simulate a 2 lead wire RTD using a VCR however i have issues with finding how to show how the resistance of the VCR changes with control voltage. My maximum control voltage is 105v which represents the temperature. Please help

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