How to build potentiostat for potentiometry with DAQ and BNC 2110

[uc de mems]

I have a lot of noise when I measure electrochemical sensor that has range -200 mV to 400 mV.

noise is on and off somehow. I have no idea why. 

I have DAQmx and BNC 2110. 

Please,help me.... 

[Doug_L._Bear]

What noise levels are you seeing?  What environment is this measurement taking place in, what input type do you have specified, analog input?  Is it Differential, RSE, or NRSE?  Can you attach a picture of the waveform you are acquiring with the noise on it.  What version of the DAQmx driver are you using?

Read the following article as well which may be useful:

http://zone.ni.com/devzone/cda/tut/p/id/3344

Message Edited by Doug L. Bear on 12-28-2009 01:24 PM

[Dennis_Knutson]

Since the BNC 2110 is just a dumb terminal block, also please specify the actual DAQ device that you are using.

[uc de mems]

I use PCI 6251.

It is analog input.

I talked technical support engineer. And he said I need external amp and filter(low pass).

I am still have no idea how to build it.

[rolfheinrich]

Sorry, but there is something wrong with your question in the subject line "How to build potentiostat for potentiometry with DAQ and screw terminal?"

Perhaps you did mean "How to connect a potentiostat to a DAQ with a screw terminal". A potentiostat is a quite complex device by its own, and you cannot build it with a DAQ and a screw terminal. You can get away with a cheap purely analog potentiostat (~450 EUR) if you want to use it together with a DAQ device like the NI PCI-6251. 

Perhaps you did mean "How to replace a potentiostat for potentiometry by a DAQ with a screw terminal". While Potentiostats can be used for potentiometric measurements, they are not really necessary. If you really want to measure only potentials with a two-electrode configuration (no currrents, no three-electrode configuration), then you need only a voltmeter with a very high input impedance some terra ohm (TΩ) will be good for almost all applications.

The input impedance of the NI PCI-6251 is "only" 10 GOhm (GΩ), and that is not that bad. Depending on the electrochemical system that you are going to investigate, this might be sufficient, so you would connect the working electrode to AI0 and the reference electrode to AI8 and you would put the DAQ in differential mode and could directly read in the voltage.

You may want to compare the results obtained by this way with the potentiometric measurement using a pH meter (~10¹⁴ Ω) that you need to put into mV mode. If you observe large differences, then you cannot connect the electrodes directly to the DAQ but need indeed to use an intermediate high impedance (at least some TΩ) operational amplifier. If you are still suffering intermittent noise, then you would employ a low pass filter between the DAQ and the operational amplifier.

Best regards

Rolf

[uc de mems]

Thank you for your answer.

I tried what you suggested. And there is still a lot of noise.

And PCI-6251 doesn't have AI08 port.

 Looks like buying pH meter will be the easiest way.

[uc de mems]

Thank you for your answer. You are right. It is very useful for me.

I got Signal Conditioning set from my advisor today. And I have SCC-LP01(25Hz LPF) & SCC-FT01(Feedthrough) in it.

I am wondering if I need to use AMP for my experiment. If it works, I have plan to buy more for multiple measuring since my sensor is a multiple sensor.

[rolfheinrich]

---

uc de mems wrote:

Thank you for your answer.

I tried what you suggested. And there is still a lot of noise.

And PCI-6251 doesn't have AI08 port.

 Looks like buying pH meter will be the easiest way.

---

I own two NI PCI-6251 boards and I use them for electrochemical measurments together with a potentiostat. Mine do have ports AI0 to AI15. AI0 is pinout #68 and AI8 is pinout #34. (look here at page 15:  http://www.ni.com/pdf/manuals/371291h.pdf)

Best regards

Rolf 

[uc de mems]

Thank you for your answer. You are right. It is very useful for me.

I got Signal Conditioning set from my advisor today. And I have SCC-LP01(25Hz LPF) & SCC-FT01(Feedthrough) in it.

I am wondering if I need to use AMP for my experiment. If it works, I have plan to buy more for multiple measuring since my sensor is a multiple sensor.

[rolfheinrich]

---

uc de mems wrote:

...

I am wondering if I need to use AMP for my experiment.

...

---

Hard to say whether you need operational amplifiers without knowing anything about your electrochemical sensor. You would need two op.amps. for each sensor, and you would place one op.amp. as voltage follower (http://en.wikipedia.org/wiki/Operational_amplifier_applications#Voltage_follower) to each line, i.e. one voltage follower interconnects the sensing electrode with AI(n) and another one interconnects the reference electrode to AI(n+8). Simple op.amps. chips cost a few cents, and you might want to experiment if you can uses the 5 V power line of your DAQ board as the power supply for the op.amps. Many years ago I used a 9 V block battery for this.

Best regards

Rolf