Saturday, October 18, 2008

Modeling Temperature Behavior in LTSpice

Modeling temperature behavior in LTSpice.

I'm working on a temperature controlled amplifier using a thermocouple and operational amplifier. The simple circuit is shown above. The operational amplifier simply amplifies the thermocouple input voltage. The thermocouple input voltage is obviously a function of the temperature (measured between the reference junction and the measuring junction). For modeling purposes, the thermocouple is modeled as a voltage supply.

To simulate the changes in voltage as a function of temperature, setup a sweep in LTSpice using the .step command as shown. Next, establish a parameter using the .PARAM command, creating a new variable as a function of the sweep. This variable can then be used in the circuit. In this example, the "thermocouple" supply voltage changes based on the 'THERM' variable. The voltage graph shows output voltage as a function of temperature.

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