Using USB-9211 to measure a small voltage - apparent signal offset?

Hi,
I wish to acquire a small voltage signal (0-20mV) using USB-9211. I know that this device is designed for use with thermocouples, but I have been informed that it can also be used for measurement of small voltage signals (24 bit resolution over +/- 80mV range).
The problem I am having is that the device seems to generate a small voltage (~3.2mV), which causes a degree of 'offset' in the signal I acquire. My first guess is that this is caused by the internal CJC of the device, however I cannot find any way of removing this signal within LabView. If this is the case, is the magnitude of the offset dependent on the temperature of the device itself?
Can anybody confirm what the source of this voltage is, and advise what is the best way to acquire my signal through LabView?
I have already raised this query with the helpdesk (ref #613180) but have not yet had a definitive answer.
Many thanks
Pete

On Feb 5, 7:10 am, peteryoung <[email protected]> wrote:
> Hi,
>  
> I wish to acquire a small voltage signal (0-20mV) using USB-9211.  I know that this device is designed for use with thermocouples, but I have been informed that it can also be used for measurement of small voltage signals (24 bit resolution over +/- 80mV range).
>  
> The problem I am having is that the device seems to generate a small voltage (~3.2mV), which causes a degree of 'offset' in the signal I acquire.  My first guess is that this is caused by the internal CJC of the device, however I cannot find any way of removing this signal within LabView.  If this is the case, is the magnitude of the offset dependent on the temperature of the device itself?
>  
> Can anybody confirm what the source of this voltage is, and advise what is the best way to acquire my signal through LabView?
>  
> I have already raised this query with the helpdesk (ref #613180) but have not yet had a definitive answer.
>  
> Many thanks
>  
> Pete
The offset is dependent upon the temperature of your cold junction.
To prove this try heating the cold junction with a hair dryer with
your signal leads shorted.
Howard

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