Current Sense Amplifier Error when using negative voltage

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
Yes in the positive direction it works perfectly. But when the supply is negative here is my problem. I need a common mode voltage range to start from -22V to 22V or more.
 

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
I tried to simulate it. In this exact case it may seem working but look what happens in certain configurations:
1661015715916.png
Here it works but if we increased R4 a bit, this would happen:
1661015787103.png
Using Vout I can still calculate the current across R33, but the current across it is different than the one around R4. Do you know what would be the problem?
 

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
I can't put such resistors in my circuit. Basically, the load is a combination of resistors that changes their values over time as they are electrodes.
However, in the below image they are the same but the same problem:
1661019391565.png
 

DickCappels

Joined Aug 21, 2008
10,245
@Nabil Miri , can you provide a complete and concise description of what your circuit needs to do? That's the first step for any good design. With that some recommendations can be made.

Naturally, if the specifications keep changing, people will be less inclined to provide help.
 

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
Ok, sorry for any misconception I created.
In a nutshell, I have a circuit that is connected to 3 electrodes (simulated as 2 resistors). This circuit senses the difference in voltage between 2 of the electrodes and change currently passed through the other 2 (not very important info but just in case).
1661036401353.png
The opampsource is a sinusoidal +-5V. I need to know the current flowing through this circuit which ranges between 1mA to 1A. First, I tried to put a voltage follower at WK point but it didnt work as it should output current similar to the one following in the circuit. The ideal works but when introducing a realistic one it doesnt.

Currently, I am trying to use a shunt resistor with a current sense amplifier to measure the current. One thing is that I cant place it either between the Rc and Rw or under Rw as it is an electrochemical electrodes and solution realisticly. Thus, it could only be placed where R211 is. Note: these resistors (Rc and Rw) values changes and are not fixed.

I am trying to find a current sense amp capacble of measuring current in both directions and ranges betwrrn 1mA and 1A for my circuit.

So, I am hoping that now it is more clearer. Thanks.
 

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
hi Nabil,
Have you considered this Hall effect current sense module, totally isolated?

E
https://www.youtube.com/results?search_query=acs712+current+sensor
I have looked into what you recommended. I found one that is Bidirectional and can measure +-2.5A.
1) But is there a certain voltage drop around its terminal?
2) and do they write how much voltage it could handle around its terminal or it doesn't it makes sense bec it acts as a wire?
3) regarding the sensitivity, for example for "ACS70331EOLCTR-2P5B3" module, they wrote that the sensitivity is 200mV/A. Does anychange of current less than 1A, wont be seen by the sensor or is it a general equation? so what is the minimum resolution or current it can sense?

Datasheet: https://github.com/SeeedDocument/Gr...31/raw/master/res/Current_Sensor_ACS70331.pdf
 

Thread Starter

Nabil Miri

Joined Jul 20, 2022
44
OK, thanks a lot, Eric. I will look more into it.
Do they say what the minimum resolution of the sensors is? I mean what is the min change in current that could be converted to a change in voltage?
and can it for example sense 1 mA?
 

ericgibbs

Joined Jan 29, 2010
19,073
hi Nabil,
Checking the attached d/sheet for the sensor, I would say the compound possible causes of errors for values near 0mA, would not ensure a current reading accuracy or resolution in the order of a few milliamps.

Read Page #21 Fig #9 of this attached data sheet.

I would recommend that you contact Allegro to confirm my conclusions

E
EG 1360.png
 

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