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Using Labjack U3-HV to obtain results from Potentiostat for cyclic voltammetry

U3-HV Potentiostat Cyclic voltammetry

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#1 sepehr

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Posted 12 August 2013 - 08:06 AM

Hi, 

I am a student at University College of London and working on an electrochemical project to measure corrosion rate of steel. I have an analogue potentiostat, which I need to read out current output (converted to voltage) from it, in order to plot Current versus Voltage graphs (i.e. Cyclic voltammetry).

I am new to data acquisition hardwares and softwares, so i would very much appreciate and be grateful to any help on this matter. 

 

I have connected the Voltage control on the potentiostat to the Analogue output on my LabJack U3. Is that right? or I should connect it to Analogue input instead? 

I also connected the current output (converted to voltage) from the potentiostat to the analogue input of my labjack U3. Is that correct?

 

In Cyclic Voltammetry experiment, you apply voltages in a specific range (e.g. 0.5 to 1.5V) in a specific time (like 10mV/sec) then you monitor the current. So the potentiostat I am using (Bank MP 81) has two analogue voltage terminals. (one for the voltage control and one for the current(converted to voltage) output). My aim in using the LabJack is to login the two potentiostat output channels and save them in a file for future analysis. I want to have current versus voltage graphs at the end. I am planning to use DAQFactory software for this purpose. 

 

From my readings through the Forum, i know that I have to use Stream mode in DAQFactory but as I said I have no background knowledge and I dont knot how to go about this problem. Thank you very very much for your held and time. 



#2 LabJack Support

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Posted 12 August 2013 - 11:11 AM

On DAQFactory side, take a look at the DAQFactory examples. There are a couple of stream examples:

 

http://labjack.com/s...ples/daqfactory

 

Also, take a look at the DAQFactory page on our site as it provides a tutorial and app guide.

 

http://labjack.com/s...ions/daqfactory

 

I'll have some else here respond back to the hardware side and connections.



#3 sepehr

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Posted 12 August 2013 - 03:56 PM

Thank you very much indeed for the information. I will have a look at the links you provided.

 

I will be looking forward to hear back about the hardware and connections. Thanks 



#4 LabJack Support

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Posted 13 August 2013 - 06:11 AM

With my limited knowledge of the equipment you are working with it sounds like you have the connections correct. Have you tried your setup?



#5 sepehr

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Posted 13 August 2013 - 06:30 PM

Yes, i just tested it today and it worked. Thanks a lot



#6 sepehr

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Posted 20 August 2013 - 09:53 AM

Hi, I have a very weird problem that I can not solve. I am trying to measure my voltage output using my Labjack U3-HV, but I keep getting wrong results. 

 

When I connect the wires to a normal voltmeter, i get correct results (i.e. -0.75 to 0.81 volts), however, when I connect the wires to the labjack device, I get one value of 0.79 and no variation. I have tried almost every thing and could not sort this probelm out. Could you please assist me on this matter. Thanks a lot. 

I have attached a photo of my wiring as well. Thanks

 

photo (6).JPG



#7 LabJack Support

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Posted 20 August 2013 - 10:19 AM

I am a little confused on output signal from your potentiostat.  Is it a current source or a voltage source.  I believe you are saying that the potentiostat measures current, converts it to a proportional voltage output, and thus the output terminals are a voltage source.  What is the range of voltage you expect versus your expected currents?

 

I can't see real clear, but it looks like you are using AIN3/GND to measure the voltage signal from the potentiostat.  If you connect the DVM to AIN3/GND at the same time, does it show the same voltage as the U3?

 

If you remove the connections to DAC0 & DAC1, and use something else to control the potentiostat, does that make a difference on the voltage readings from AIN3/GND?

 

Do you have any more technical details or electrical specs for the input and output terminals on the potentiostat?



#8 sepehr

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Posted 20 August 2013 - 11:11 AM

Yes exactly, the potentiostat converts current to voltage itself, so the output terminals are voltage source. I am expecting voltage output from -0.74 to +0.84. This voltage output is proportional to current, so I will plot input voltage (0.5 to 1.5) versus current (converted to voltage) out put (-0.74 to +0.84). 

 

When I connect the voltage output from the potentiostat to DVM instead of labjack AIN3/GND, DVM shows the correct range of out put (i.e. -0.74 to +0.84). But when I connect it to the labjack it doesn't show any variation. 

 

I cant control the potentiostat using anything else, as the potentiostat is connected to three different electrodes in order to produce output. But I wanted to see if AIN0 terminal works or not and I connected the labjack to a power supply and change the voltage on the power supply and it gave the same results on LJControl Panel, so it does work.

 

I have no idea why it works with DVM and doesn't work with Labjack. 

Thanks



#9 LabJack Support

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Posted 20 August 2013 - 11:23 AM

When I connect the voltage output from the potentiostat to DVM instead of labjack AIN3/GND, DVM shows the correct range of out put (i.e. -0.74 to +0.84). But when I connect it to the labjack it doesn't show any variation.

 

 

I understand, but what if you connect the DVM to AIN3/GND at the same time.  Does the DVM show the voltage you expect, or same voltage as the U3?



#10 sepehr

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Posted 20 August 2013 - 04:30 PM

I will try that tomorrow and will let you know. Thanks 



#11 sepehr

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Posted 25 August 2013 - 06:57 AM

Hi, I realised the problem was to with low input impedance of the HV unit. I tried it with another Data logger and it worked. So i might buy Labjack U3-LV, which offers 40 MegaOhms input impedance to solve the problem and use only one unit rather than 2 converters that I am using now. 



#12 LabJack Support

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Posted 26 August 2013 - 12:46 PM

The U3-HV has low voltage channels same as the U3-LV.  Just try FIO4.  Note, though, that the low-voltage analog inputs cannot read to -0.74 volts.  The most negative you can read is about -0.3 volts:

 

http://labjack.com/s...users-guide/2.6

 

Other options to provide a higher-impedance input that works from -0.74 to +0.84 volts are using the U6 or T7 instead of the U3, or with your U3 you could use the EI-1040 amplifier to buffer the signals:

 

http://labjack.com/u6

http://labjack.com/t7

http://labjack.com/c...ation-amplifier

 

One other option is to use an op-amp to make your own buffer, but you would need to provide a small negative power supply for the op-amp so it can handle the -0.74 volts.



#13 sepehr

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Posted 03 September 2013 - 11:26 AM

Thank you very much indeed for your helpful information. Appreciate it





Also tagged with one or more of these keywords: U3-HV, Potentiostat, Cyclic voltammetry

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