SCXI1102

[MSS]

Dear SCXI 1102 users,

were anyone getting 0.01 Deg.C resolution when SCXI 1102 with RTD sensor is used for temperature measurement?

Thanks in advance

With regards

M.S.Senthilkumaran

India

[McKala[DE]]

Hello M.S.Senthilkumaran,

I'm not sure if you are asking for testimonials of people or if you are interested in seeing if this is possible.  If you are interested in determining the resolution of your system, you can use the Accuracy Calculator to find the maximum error of your DAQ system and then you can reference this KB to determine how accurate your sensor itself is.  The total error would be the max error for your system.

If you are looking for testimonials, I'll let other people pipe in 

Regards,
Micaela

[MSS]

Hello micella,

Yes mean the testimonials.

accuracy calculator is usefull to find accuracy of the hardware but my question is about resolution.

Thanks in advance

M.S.Senthilkumaran

[Henrik_Volkers]

M.S.Senthilkumaran,

the resolution of your analog RTD is infinit (OK, limited by noise)   

look at the spec of your 1102, its a analog amplifier/filter ...  resolution ? (see above) 

and it's ending at ...?

So, what do you think is the limiting device? 

What does is measure ? R?

PS:I should have used another login... this answer will get a bad rating

Message Edited by Henrik Volkers on 06-22-2006 10:14 AM

[Logan_K]

I will expand on where Henrik was trying to lead you with his questions...

The main limiting factor on being able to sense a small change in the RTD (i.e. resolution) is going to be noise. Assuming that the RTD's noise is negligible, then the main source of noise in the measurements is the SCXI-1102. The averaged noise specification of the SCXI-1102 is 5uV, which means that any voltage change from the RTD smaller than 5uV will be lost in the noise.

If you use a very stable 100uA current source (the SCXI-1581 is the most common solution for RTD current excitation) then at 0degC a voltage change of 5uV on a 100 ohm RTD is equivalent to about a 0.13degC change in the RTD measurement. So, 0.13degC is the smallest temperature change that you will be able to sense at 0degC from your RTD - assuming that there is no noise from the lead wires of the RTD.

Let's say that you were able to average your data long enough that you could get the noise down to 1uV - this is still only 0.025degC of resolution. If you average your data for that long, I am willing to bet that the actual temperature has probably already changed by much more than 0.025degC.

The NI-4070 is probably the only solution from NI that will be able to give you a resolution of close to 0.01degC for an RTD.

Logan K
National Instruments R&D

[MSS]

If its the limitation of the scxi 1102 then how its change in value is 0.01 deg.c in calibration tab in the max?

[Logan_K]

In my previous post, I was describing the theoretical maximum resolution of the SCXI-1102. Inside the MAX calibration tool, it simply returns the averaged data, and if it appears to be more stable than 0.01 degC, then that probably means that your particular SCXI-1102 is performing better than the specifications, which isn't surprising. If you could be more clear about what you are trying to accomplish, maybe I could be of more help.

Regards,
Logan

[MSS]

My question is, I am getting 0.01Deg.C resolution in Daqmx Calilbration wizard but why I am not getting the same in labview program(in labview program 0.06 Deg.C)?

As you said let us assume SCXI 1102 is performing better than specified. In that case its performance should be same every where isn't it? But why there is an difference as said above, even it is not matching with the theoritical calculation given by you in your earlier post. What is the reason?

I hope this will be clear for you.

[Logan_K]

In LabVIEW, are you averaging the data? If so, how many points are you averaging at a time? Also, when you say that LabVIEW gets 0.06degC - is this the magnitude of the noise you are reading, or is it the overall deviation from the expected temperature? Finally, when you configure your task in LabVIEW, what are your input limits?

-Logan

[MSS]

Wat is the resolution of SCXI 1102 module with PXI MI 6221 daq combination and not the accuracy of this device?