IoT Design Needs Basic Knowledge of Measurement and Calibration


With IoT being 90 per cent sensor-based, designers have to learn ‘how to measure’ and ‘how to calibrate’

By Srinivasa Moorthy S A

I have been working with two start-ups which actually uses Internet of Things (IoT) for their products. Both of them have to measure certain parameters and use sensors. When they went for the proof of concept (PoC), customers told them their measurements don’t meet their clients’ requirements. Both the start-ups reached out to me and told me they had used the best sensors, and in their labs, they have done measurements and found ‘the readings are fine’.

When I sat with one of the team, I found they have used about 20 ‘Things’ to measure 20 voltage sources. The client’s specification is 10mV variation for 2V source. When we sat and measured each thing, we found each of them showed a different voltage. So, I asked them did you calibrate your ‘Thing’ and the answer was the sensor is pre-calibrated and there is no need to calibrate the system.

Analysis and solution

Then I asked does your ADC in the microcontroller has sufficient precision and how did they design the analog front end to interface the sensor. Now the fun started:

  • They have used an opamp (street grade) and never did the Worst-Case Analysis (4 corner) for the components and have no clue on the how decide the tolerances for the resisters.
  • The ‘Thing’ doesn’t have an internal reference for self-calibration, and it took a lot of time for me to convince them that even if the sensor is calibrated, other circuits will introduce variations and every piece of the ‘Thing’ needs to be calibrated. (It is another story that they never heard about Standard Voltage sources used for calibration.
  • I asked them whether they know Gage R&R (repeatability and reproducibility) and how that has to be applied to these so called ‘Things’. They had no idea about this stuff. Unfortunately, the client is someone who understand and uses the stuff in their line.

This resulted in an aborted trial and now they are practically redoing the ‘Thing’ after their first misstep. With IoT being 90 per cent sensor-based, designers have to learn ‘how to measure’ and ‘how to calibrate’. Unfortunately, I have noticed that the curriculum doesn’t teach them all this (with the exception of instrumentation students but they also don’t know why these things have to be done.

Srinivasa Moorthy S A is the Chief Executive Officer of the Andhra Pradesh Electronics & IT Agency. He has over 30 years of experience in the IT industry as Head, Leader & Technocrat in the Electronic Product Design & Engineering Services.