Temperature-dependent impedance measurement system
Automating an LCR meter to sweep impedance across frequency while controlling and logging sample temperature.
Built with Sohum Biswas at the Smart Materials Lab, IIT Indore.
The goal
The lab had a capable LCR meter (a Newtons4th PSM1735 NumetrIQ) sitting mostly unused. We wanted to make it easy to run temperature-dependent impedance measurements: sweep across frequencies, log the sample temperature, and capture everything to Excel with live plots, all from one application. The target range went down to −200 °C.
An LCR meter applies a small AC signal and measures the resulting voltage and current. From that it derives inductance, capacitance, resistance, |Z|, phase, Q-factor and loss tangent. Sweeping the frequency builds up Bode or Nyquist curves that characterise dielectrics, sensors and thin films.
It took three tries
Try 1: the lab’s iTherm ULT-99 controller. We spent a lot of effort decoding its Modbus protocol, then found out it only goes down to −99 °C. We abandoned it.
Try 2: thermocouple + MAX31856 + ESP32. The wiring worked and the readings checked out, until the thermocouple junction got accidentally cut. A makeshift repair wasn’t good enough, and we lost two days.
Try 3: PT100 + MAX31865 + Arduino Uno. We switched to an industrial PT100 RTD with a MAX31865 converter. The Arduino runs PID control and switches heating through a relay. Temperature control was stable and reliable, and this is the version that works.
What the software does
- Talks to the PSM1735 over USB using its ASCII command set
- Runs frequency sweeps and records the full set of impedance parameters
- Logs temperature alongside every measurement
- Plots results live and exports to Excel
Thanks
Prof. Somadiya Sen for lab access and the idea, Mohd Vasim Sir for guidance, and the lab team.