pH measurement - how to design input amplifier

[kekon]

ina116 ph

I intend to design pH measurement circuit using classic pH glass electrode. As one knows pH probe needs to be connected to an amplifier with very high input resistance. Typical internal resistance of pH elekctrode is very high (about 400 MOhms). At a rough guess one might choose such amplifiers as TL071 with its input resistance of 10^12 Ohms. Obviously such device is probably an improper solution for it is not precision operational amplifier. Unfortunately I didn't manage to find any schematics or pieces of advice how to design such amplifier. Does anyone know where can I find it ?

 

[glenjoy]

ina116p samples

Hi, you can get an amplifier with a very high input impedance at National Semiconductor, I just forgot the part number.

For the whole amplifier setup, look for a design of instrumentation amplifiers.

 

[IanP]

ph ina116

If you are seriously looking at good instrumentation amplifiers you should try the Analog Devices offer at : **broken link removed**
Try, for example, the AD620 ( **broken link removed** )
It is really a very good instrumantation opamp, and you should be able to obtain some samples for free ..

 

[kekon]

ina116

Thanks for help. OPA627 seems to be the best device. It has 10^13 Ohms input resistance which suits me fine. The disadvantage is its price... However, obtaining any electronic devices is no problem for me (the problem is the price in some cases)

 

[daitoupipi]

lmc6001 ph

INA116 may be a good choice.

FEATURES
l LOW INPUT BIAS CURRENT: 3fA typ
l BUFFERED GUARD DRIVE PINS
l LOW OFFSET VOLTAGE: 2mV max
l HIGH COMMON-MODE REJECTION:
84dB (G = 10)
l LOW QUIESCENT CURRENT: 1mA
l INPUT OVER-VOLTAGE PROTECTION: ±40V

APPLICATIONS
l LABORATORY INSTRUMENTATION
l pH MEASUREMENT
l ION–SPECIFIC PROBES
l LEAKAGE CURRENT MEASUREMENT

 

[wholx]

measurement ph input amplifier

hi kekon,
i have worked on a project to design a portable pH meter. in the pre-amp circuit, we used the AD822. however, the measurement mechanism wasn't based on pH glass electrodes.

 

[windman]

I'm sure you can use INA116P to achieve what you need. I used it once to measure the low current as weak as 10fA.

 

[wzdreamer]

National LMC6001 ... you can see pH meter example in the datasheet LMC6001 + LMC6042...

Someone, who is familiar with residual chlorine metering?

 

[is_razi]

hi kekon,
i have worked on a project to design a portable pH meter. in the pre-amp circuit, we used the AD822. however, the measurement mechanism wasn't based on pH glass electrodes.

dear wholex ,
i saw that you have worked on a ph meter .
i want to design a ph meter for my final project.so if it's possible please share your experiences with me.
yours sincerely.
:roll: