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Analog input resolution when using a reduced measurement range

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Hey everyone!

I have a question regarding measurement resolution. Let's say I want to measure a change of a few uV in a voltage that typically reads between 50 uV and 1 mV. The voltage input DAQ device I have is specified at -10V to +10V, with a resolution of 24 bits. That gives me a resolution of 20V / 2^24 = 1,19 uV. So question 1, is this understood correctly? 

 

Question two, what happens if I set the DAQ device to read only, say, -1V to +1V. Does it use the resolution over this new, reduced measurement range, or will the resolution always be 1,19 uV no matter what my measurement range is (and what is then the point of being able to reduce the measurement range)?

 

I get that there is a practical limit, I can't reduce the measurement range indefinitely for infinite resolution, I am just asking broad terms here. 

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Accepted by topic author Thraundil

Your understanding is correct. When you change the measurement change, voltage reference of the ADC is also changed appropriately.

-Santhosh
Semiconductor Validation & Production Test
Soliton Technologies
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@Thraundil wrote:

Hey everyone!

I have a question regarding measurement resolution. Let's say I want to measure a change of a few uV in a voltage that typically reads between 50 uV and 1 mV. The voltage input DAQ device I have is specified at -10V to +10V, with a resolution of 24 bits. That gives me a resolution of 20V / 2^24 = 1,19 uV. So question 1, is this understood correctly? 

 

Question two, what happens if I set the DAQ device to read only, say, -1V to +1V. Does it use the resolution over this new, reduced measurement range, or will the resolution always be 1,19 uV no matter what my measurement range is (and what is then the point of being able to reduce the measurement range)?

 

I get that there is a practical limit, I can't reduce the measurement range indefinitely for infinite resolution, I am just asking broad terms here. 


Have a look into the specifications!  It should give an idea of the actual limits. And don't mix resolution with accuracy! 😉

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

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@santo_13 wrote:

Your understanding is correct. When you change the measurement change, voltage reference of the ADC is also changed appropriately.


That is not true in general, there are DAQ-devices with several input ranges (e.g. NI-9205), and there are others with only one input range (e.g. NI-9223).

Like Henrik said, always have a look at the specs of the device.

Kudos are welcome...
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Agreed with both of your points, if the device has only one measurement range, configuring a different min/max value during DAQmx Task creation will not have an impact on the resolution.

 

My answer was based on if the device has multiple ranges like DSA card (since the question specified 24-bit).

-Santhosh
Semiconductor Validation & Production Test
Soliton Technologies
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