## Measuring differential voltage

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Hi,

i'm looking for a simple hardware circuit that delivers the differential voltage from two voltages.
It is an AC voltage of about 0.5 to 5V which is measured before and after a resistor.
Is it possible to use an OP TL071CN, for example?
I would like to read the signal into a controller and continue working on it.
To make it fast I do not want to read the two voltages with the controller and then form the difference!

greetings

Wolfgang

Not enough information.

You will have to provide a rough schematic for ground, your resistor, its value, what it is connected to, how much current is flowing through it, etc.

What is the frequency of the AC signal?

50/60 Hz Mains or up in the KHz range?

"To make it fast..."

How fast?

What are you trying to control?

JC

I want to measure the conductivity of water.
There are two contacts in the water.
At the contacts, I put an AC voltage and then measure the current flowing. I did a test with a function generator and an ammeter.
At a frequency of 100Hz and a voltage of 2V I measured 126mA AC. At 1000Hz, it was 230mA.
The value of the voltage ect. I read into a controller that also generates the frequency.

Not enough information?

Last Edited: Sat. Nov 18, 2017 - 10:34 PM

There have been several/many threads on "conductivity probes" -- try to search them out.

Indeed doing a push-pull is almost always desired, to avoid probe plating.

100+mA sounds like a lot, IME.

A channel from one of our production designs.  The switchable resistors help with ranging.

IC5/pin 7 is the circuit output channel that goes to an AVR ADC input.  The signal near "D6" is the conditioned thermistor reading, which goes to another ADC channel.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Last Edited: Tue. Nov 21, 2017 - 03:51 PM

Kind of fun to take one of these apart...

https://www.ebay.com/itm/TDS-Met...

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.