Measure current in an electrolysis process

[UroBoros]

electrolysis mosfet

Hello

I need to measure the current in a electrolysis process. Maximum current is 500ma. I need to monitor the current continuously for over current etc. I need 9 channels.

I am not having very good idea on how to do the hardware part .PIC software I can manage.
This is the image i propose to get an idea of my requirement

If my required range is 0to 500ma can somebody help me with good hardware design suggestions. I need to measure 9 channels like this .But I think i can do it by analogue multiplexer chips. Also suggest a chip for my purpose.
Please suggest a a suitable series resistor to make PIC calculation simple. I need only a resolution of 1mA.
Thanks

 

[chevymn1964]

Check out the MAX4080SASA... Its a current sense IC & It works great

 

[UroBoros]

Check out the MAX4080SASA... Its a current sense IC & It works great

Thanks for the link.
My problem is I need to implement this for 9 channels in my system. So footprint and cost is a issue. More than that I do not need high precision . The shunt resistor voltage measurement method will do my purpose. I believe!

Thanks

 

[garg29]

Hi Roy,
check the attachment.

 

[garg29]

take care of resistor wattage

 

[FvM]

The circuit would require a MOSFET with sufficient voltage rating and logic-level gate drive, to allow control from a PIC. IRF523 (not an active part BTW) has neither.

The shunt voltage drop further reduces gate drive voltage, thus it has to be designed sufficient low, e. g. 500 mV using an 1 ohms shunt. For 1 mA resolution, the shunt voltage has to be amplified to at least 2.5 volt.

 

[UroBoros]

The circuit would require a MOSFET with sufficient voltage rating and logic-level gate drive, to allow control from a PIC. IRF523 (not an active part BTW) has neither.

The shunt voltage drop further reduces gate drive voltage, thus it has to be designed sufficient low, e. g. 500 mV using an 1 ohms shunt. For 1 mA resolution, the shunt voltage has to be amplified to at least 2.5 volt.

Thanks Amith for the schematics.
Forget about MOSFET, Can I use a PNP transistor because of the dropping resistor? Max only 500ma so why cant we go with a transistor?

Thanks

 

[FvM]

Not PNP but a NPN with sufficient current gain at 500 mA would be reasonable.

 

[UroBoros]

Not PNP but a NPN with sufficient current gain at 500 mA would be reasonable.

I meant to use PNP with shunt in collector so that it wont effect switching.

btw one change in requirement.

I need .1mA resolution upto 500mA. (Total 5000 ADC divisions)
Which is a reasonabily prized chip for my purpose?
I need 14 bit ADC in that case.
Regards

 

[kender]

My favorite application notes on current sensing:
**broken link removed**
broader app note on current sensing. It covers both resistive and hall-effect sensors: **broken link removed**

 

[UroBoros]

Hello

I have drawn a circuit to switch my probes.
btw I am learning Proteus also. I have simulated this circuit in Proteus and seems to be working as required.(As far as I know about simulation)
Please suggest the consequences of my plan if any. Since I was not able to locate the part number of LOGIC level MOSFETs widely available,I was not able to select one from my local market. But from IRF520 data sheet I felt it can conduct my currents (Less than 1 amps) at 5V in gate.(Right?)
This is my design.


Thanks