ph meter high impedance problem

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garg29

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op amp for ph meter

hi all,
m designing a ph meter using ca3140 for the first stage wherein m directly connecting the probe of the ph electrode to pin 3 of the opamp and thru pin 2 feedback is attached... and also tried attaching 100k & 10M resistance in between pin 3 and electrode... but since the impedance of the probe is high m not getting proper results...what should i do? please help me out
 

ph meter opamp

The CA3140 has input "resistance" > 1TΩ, what should be good enough ..
You have to be extremaly careful with connectors, IC-sockets and materials (PCB, for example) you use between the opamp's (+) input and the ph-probe ..
Compare your design with this one:
https://www.emesystems.com/OL2ph.htm
Maybe it will give you some clues ..

Regards,
IanP
 

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