Averagning

Hi,

I got a pH probe having the differential output. It is working but the output is very shaby.

I always fluctuates from the actaul reading to some extend in + and - side. I want to make it stable either by averaging the output or some other hardware technique.

Somewhere i read that the capacitor could be used to get the stable output (i.e the capacitor alone can do the averaging itself to some extend).

It's true???

Vikky said:

Hi,

I got a pH probe having the differential output. It is working but the output is very shaby.

I always fluctuates from the actaul reading to some extend in + and - side. I want to make it stable either by averaging the output or some other hardware technique.

Somewhere i read that the capacitor could be used to get the stable output (i.e the capacitor alone can do the averaging itself to some extend).

It's true???

Click to expand...

hi,
If you post your circuit diagram, it maybe possible to suggest a hardware solution to the 'signal jitter'.

Vikky said:

Hi,

I got a pH probe having the differential output. It is working but the output is very shaby.

I always fluctuates from the actaul reading to some extend in + and - side. I want to make it stable either by averaging the output or some other hardware technique.

Somewhere i read that the capacitor could be used to get the stable output (i.e the capacitor alone can do the averaging itself to some extend).

It's true???

Click to expand...

Hi Vikky,

A pH probe has a very high output resistance, so it gets pulled down and unstable by even a very light load; you need something with an extremely high input impedance. Take a look at a very simple pH amplifier. That isn't the one I would settle for, though.

Study differential amplifiers, and more to get ideas about small signals which may get lost in noise. Ideally, an instrumentation amplifier would be the best choice.


Edit: Hi Eric. did it really take me that long to type that?

If you post your circuit diagram, it maybe possible to suggest a hardware solution to the 'signal jitter'.

Click to expand...

The circuit is very simple though i have not constructed it using any software. I have connected the reference output of the pH probe to the unity gain amplifer connected to virtual ground (since working with single supply). The measuring electrode signal is also passed through unity gain amplifier and then in the next stage i am just taking the difference of then will the require slope. I am getting the result but it is constantly fluctuating at the expected value.

A pH probe has a very high output resistance, so it gets pulled down and unstable by even a very light load; you need something with an extremely high input impedance.

Click to expand...

Actually i got two different kind of pH probe with the nearly equal slope (mv/pH). This problem arise with the second kind of probe. The first one is working fine and giving me the stable output with the same circuit.

hi Vikky,
Your description dosnt tell us, what OPA's are being used, the power supply source etc.

In order to help we need to see a full circuit diagram showing the components and values.