pH sensor

ericgibbs · Sep 9, 2009

Vikky said:
I have MCP607. I even tried to built it my adding the voltages at the initial stages. Here is the new schematic attached. I gives 600mv at 0mv input. But at the extreme it fails like +413 should give 100mv and -413 mv should give 1100.

Their is the differene of 50mv on both side.

hi,
Looked at your drawing, where did you connect the probe.?

Also would a minimum pH of 2 thru to 14 be acceptable.?

3v0 · Sep 9, 2009

I went back to the first post to see what this was for. I found this.

I am developing pH meter should be working from 0- 14 pH. For this i got a pH sensor from

ericgibbs · Sep 9, 2009

hi,
Look at this option, just shows the basic circuit.

The -Vref should be derived from a voltage reference and be adjustable.

Note: for the MCP607 the recommended -Vsig is -0.3V [not -0.413V], so there is a minimum pH signal limit.
If you used a CA3140 opa this would allow a -0.5V input.

ericgibbs · Sep 9, 2009

3v0 said:
I went back to the first post to see what this was for. I found this.

I also went thru the posts and found this

I do have such solutions capsules of 4,7,10 pH. But what should be the actual calibration steps.
Do i need to change the gain value as time passes or some other method??

ericgibbs · Sep 9, 2009

3v0 said:
What did I do wrong ???

3v0

Nothing.

I was trying show that the OP has calibration liquids for a minimum of 4pH.

Vikky · Sep 9, 2009

Looked at your drawing, where did you connect the probe.?

The probes would be connected at the V points. The refernce electrode at V1 pin and the measuring electrode at the V2 point.

Roff · Sep 9, 2009

My understanding is that the input span is -413mV to +413mV, and the output span needs to be 100mV to 1100mV. Below is a circuit that should do this. Op amps need to have CMOS inputs.

ericgibbs · Sep 9, 2009

hi Ron,

Are you saying that you want to shift the -413mV thru +413mV input range to, 0V thru +826mV or 0V thru +5V.???

yes i that to do that. Need help for the schematic

I guess we will have to see what the OP finally decides upon.

BTW:
For ref only, you may have this already, if so please ignore.
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pH sensor

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