Building the impedance measurement Circuit - Page 1
Forum section: electronics / general

author: Zainiii
author_rank: Contributor
timestamp: August 10, 2024, 12:50:02 am
content: Dear Members,I hope you are all doing well.I am a PhD student and completely new to circuit design. I need a compact-sized circuit and prefer not to use an impedance analyzer due to its bulkiness. I am looking to build a circuit capable of automatically measuring the impedance of a sensor in the range of 1MΩ to 30MΩ. However, I am unsure how to approach this task, especially with the various methods available for impedance measurement. I’m not certain which method would be most suitable for automatic measurement in my case. There are different impedance measurement modules, but none seem to have the capability to measure impedance automatically within this range. My sensor’s equivalent circuit is a resistor in parallel with a capacitor.Could someone guide me through the procedure to build the circuit design? Specifically, I would like to know which components I should purchase to begin building the circuit. If there are any tutorials or resources that you could recommend, that would be very helpful as well.So far, I have only completed the integration of a DDS (Direct Digital Synthesis) with an Arduino to generate a signal with a frequency of 1 kHz and an amplitude of 500mV, which meets my signal requirements. However, I am uncertain about how to proceed with the remaining circuit design.Your help in this matter would be greatly appreciated.

author: eugene
author_rank: Frequent Contributor
timestamp: August 10, 2024, 07:52:32 pm
content: Accurate impedance measurement is a fine art. You might consider starting with an ADuCM350 from Analog Devices.https://www.analog.com/en/resources/media-center/videos/3335880984001.htmlThere's a dev kit available with software that might do almost everything you need out of the box.https://www.digikey.com/en/products/detail/analog-devices-inc/EVAL-ADUCM350EBZ/4915063

author: jonpaul
author_rank: Super Contributor
timestamp: August 10, 2024, 08:26:01 pm
content: Read HP Impedance Measurement Handbookhttps://www.keysight.com/us/en/assets/7018-06840/application-notes/5950-3000.pdfJon

author: Zainiii
author_rank: Contributor
timestamp: August 12, 2024, 05:37:51 pm
content: Dear Sir.Thanks a lot for the reply.i see the data sheet of this module but i didn't see anywhere the information regarding the impedance measurement range of this one. Previously i used the AD 5933 which stated it can measure the impedance up to 10M ohm, but when i used the AD 5933, for every measurement i have to calibrate the AD 5933 module, and the calibration resistor and unknown resistor value should be very close to each other, which is limitation of that module, i need that module that can measure the impedance automatically like an impedance analyzer, can you recommend me that module that automatically , your assistance would be highly appreciated

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 13, 2024, 03:11:07 am
content: Quote from: Zainiii on August 10, 2024, 12:50:02 amYou did not give the capacitance, nor which value, R or C, matters most to you.The classic impedance check is to create a median copy of the R//C you expect to see and use a bridge. That gives an exact 50% waveform at the median point.If C matters most, many touch-sensor designs can measure that for you, or you can use the C to make a RC oscillator.