You have a parameter PT but it's not referenced in the circuit. Review LTspice help to learn the required syntax for parametric circuits. The component name "PT" is no correct parameter reference. Resistor component designator need to start with R, e.g. Rpt. A parameter reference for component value has the form {PT}.Hi, I am trying to run the simulation in LT Spice but I am not sure what is missing.
Problem is insufficient voltage range of AD8039. You can e.g. use AD824.The step command start working. But the output voltage is not proportional to the change in resistance at R_PT. I use step command as .step param X 1000 1600 200. There should be four points, 1000, 1200, 1400, 1600. The output voltage and also input voltage is not proportional.
It won't be when using a resistive divider for the sensor output as you have.But the output voltage is not proportional to the change in resistance at R_PT.
Inspite of all the advice given, PT100's are good but not perfectly linear. I gave the formulae for S/W error correction from TI.
I agree with you. I think the original problem was using a 50 µs transient mode test which was used when it failed. But there are other settings not displayed on the schematic. Normal or alternative simulation in setup) etc.All suggestions about Pt1000 linearization, constant current drive etc. are surely relevant but essentially not answering the more elementary problem of post #1 original circuit and follow up questions.
To recall, post #1 deals with LTspice syntax and misspelled node names, post #10 with OP output voltage range. I think it's appropriate to analyze the primary problem before advancing to improved Pt1000 sensor circuits.
Please also notice thread title.
OP output is obviously in soft saturation. You see the expected output when you put in a suitable rail-to-rail OPOn this plot , I don’t see how the Problem is insufficient voltage range of AD8039. affects the step function yet the output still worked.
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