Identifying input range in PCI-6034E

[ginos]

Also this article of NI which refers to E Series and SCXI-1102B, mentions that: 

"The appropriate gain will first be applied at the SCXI module and then at the DAQ card if more gain is needed."

Supposedly the SCXI-1102B aplies a gain of 100 in range -100mV to +100mV. This gain is not enouph since the DAQ board is able to read a smaller range (-50mV to +50mV).

Is the DAQ board going to apply a gain of 10 in the already amplified signal, so the total gain will be 100(1102B)*10(DAQ board)=1000(total)?

What would the range of voltage in case like that? 

Thanks again

Giorgos

[BROhan]

Hi Giorgos,

I wanted to point out that the PCI-6034E resolution is in terms of microVolts (uV), not mV.

Basically, you will use the gain of 100 in the first stage (SCXI 1102B). Now, your 1.203-2.436 mV signal will be a 120.3-243.6 mV signal. At this point you will need to use the +/-500mV range of the PCI-6034E in order to see all of your signal and take full advantage of the ADC. The resolution will be 15.3 uV on that signal. The "gain" of 10 on the 6034E allows you to use the full scale of the ADC, but the total amplification of your signal will be 100, with a resolution of 15.3 uV.

[BROhan]

Hi Giorgos,

Actually, ignore that last part. Essentially your gain will still be 100, but you will be using the +/-50 mV range from the PCI-6034E, as that is the best input range your DAQ/SCXI can select. And your resolution will actually be 1.53uV on your 1.203-2.436mV signal. Sorry for the confusion, but I hope that this now makes sense.

[ginos]

Thank you for your patience Rohan,

I believe that the second answer you gave me does not take into consideration the gain of the SCXI-1102B.

If the SCXI-1102B did not have an amplifier then the signal would be amplified only by the DAQ board by a gain of 100 which corresponds the ±50μV range with a resolution 1,53μV. (That I can understand). Since the SCXI-1102B has an amplifier I believe it will contribute, but how?

How the first gain contributes to the total gain?

I apolgize for my questions, but I my knowledge in electronics is limited and some things might not be that clear to me.

Best Regards

Giorgos

[BROhan · Accepted solution]

Hi Giorgos,

I understand your confusion. As the article indicates, the gain applied at the SCXI module simply allows you to read a signal within the +/-100mV range at full scale. The reading that is returned is not actually an amplified signal. So you will still read in a 1.2-2.4mV signal. As the article indicates, by configuring the voltage range, you select the amount of gain applied over the system. Therefore, if you select the +/-50mV range, you DAQ board will apply a gain of 100 and read at a resolution of 1.53 uV.

So the gains are only meant to allow you read a cleaner signal by using an onboard analog to digital converter (ADC) at full scale for the particular input range. That is why you still receive a signal that is 1.2-2.4 mV, and not something higher.

The overall gain is still 100. Once the signal is brought in through the SCXI, it is still 1.2-2.4mV. You will still need to apply the gain of 100 if you configure the input range to be +/-50mV, and your resolution is 1.53uV. Please let me know if there is anything else that is unclear.

[ginos]

Sorry for my late reply Rohan. Thank you very much for your answer.

One last question. In Measurement and Automation Explorer I can create a task under SCXI-1102B and under the PCI-6034E. Is there any difference between those tasks (in resolution for example)?

Best Regards

Giorgos

[BROhan]

If you need to pull temperature data from the 1102B, you will need to configure the task for the SCXI module. However, the DAQmx driver takes care of all the resolution concerns behind the scenes (resolution specs same as above). Basically, when you connect your PCI card to the SCXI chassis, the driver will handle the data you are bringing into the PC if you configure a task for the 1102.