Frequent calibration problem of AD 5933 for impedance measurement

Other Hardware General Electronics
1

Dear Sir,

I hope this message finds you well.

I am using the AD 5933 evaluation board for impedance measurement; The data sheet says it can measure the impedance up to 10M ohm. I am currently measuring the impedance of a microfluidic device, where I capture the bacteria that increase the impedance from 3M ohm to 8M ohm, which is within the range of 10M ohms. I have encountered an issue where, for instance, if the impedance measures 8M ohms and I use a 3M ohm resistor for feedback during calibration, I do not obtain the correct impedance value. However, using an 8M ohm resistor for calibration provides an accurate impedance measurement. So the problem is, every time I have to calibrate the AD 5933 if there are slight variations in the impedance value to get the correct result

I have a few questions:

  1. Is it possible to use a single resistor value as a feedback Resistor for calibration to measure impedance ranging from 1 ohm to 10M ohms, thereby overcoming the challenge of frequent calibration? If so, could you please suggest some solutions to address the issue of frequent calibration?

  2. I recently read a paper where the author utilized an HMC 245A switch to address the issue of frequent calibration in impedance measurement. Is this method effective? The HMC 245A switch is described as a non-reflective SP3T (Single Pole, Triple Throw) RF switch. In this paper, they used different resistors with an HMC 245A switch and it automatically calibrates AD 5933.

  3. Could you recommend a method, switch, or IC that if I combine it with AD 5933 and they automatically calibrate the AD 5933 and I get the correct impedance of my device from 1 ohm to 10M ohms without needing to change the feedback resistor repeatedly?

Your assistance in this matter would be greatly appreciated.

2

At those impedance setup is critical and any changes could be reflected in your readings. Also to measure impedance it has to pass a current through the sample, is that causing problems in your readings? Temperature of the target could possibly change readings. Can you post a picture of the setup.

3

Fortunately, you have at least one easy question here. The answer is: No. Please refer to the capabilities of your test device:

  • Impedance measurement range from 1 kΩ to 10 MΩ
  • Capable of measuring of 100 Ω to 1 kΩ with additional circuitry

An additional problem is this:

1 MSPS, 12-Bit Impedance Converter, Network Analyzer

1 Ohm - 10MOhm = 1:10,000,000 dynamic range. 12 bits = 1:4096 dynamic range. So if you define the range as 10MOhm max, this will make the smallest measurable step size around 2.4kOhm.

It sounds like a very good idea, indeed.

No. See above.