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7833R How is the analog voltage converted to a decimal value? What is 1V in decimal value?

I am using the 7833R and I'm measuring a constant 1V to determine what digital decimal value represents 1V analog signal.  I'm confused as to what this should be.  I'm getting a reading of around 6K which doesn't make any sense because if this is the case then 10V would give me a decimal value of around 64K.  Since this card can measure from -10V to +10V and the decimal value is a 16-digit number I will can't have any values for negative numbers.  Can anyone provide me with some information?
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Message 1 of 6
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Howdy,

I think you need to read up a little bit about analog to digital conversion is performed, but in short, here's some help:

The 7833R has a 16-bit A-to-D converter. 16-bits is not the same as 16 digits. Its actually a number equal to 2^16, or 65536. Think of it as 65536 separate steps, from 0-65535. Since the range of the board is +/-10V, a value of 0 = -10V, and 65535 = +10V. If the total range is 20V, each step represents 0.00030517578125 V. And each volt is equal to 3276.8 steps. Any number below 32768 is a negative number, and anything above 32768 is a positive number. Does that help?




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Message 2 of 6
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Thanks for the input.  I understand the steps but even if that is the case, when I'm putting in 1V I should then see a number greater than 32K but I'm seeing apporximately 6K.  So I looked at the impedance values of my external output which is 50 Ohms and the impedance of the Analog input signals is 1G Ohms which explains why the voltage seems to be doubled.

It seems to me that 0 - 32K represents 0 -10V respectively and that 64K represents a very small negative number.  So 64K - 32K represents a very small negative number to -10 V.

In summary:

-10V = 32768
very small negative number = 64K
0V = 0
+10V = 32767

This is what I'm seeing and can anyone verify if this is correct?

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Message 3 of 6
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What input mode are you using? DIFF, NRSE, or RSE.
 
For reference, output code versus voltage input can be found on page 2-3 of the manual
 
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"It’s the questions that drive us.”
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Message 4 of 6
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Thank you.

So on that page it states exactly as I am getting.  That means that the value of

32768 = -10V and
32767 = +10V

So the returned values are actually in unsigned integer 16.  RIght?
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Message 5 of 6
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0-65535 would fit the data range for a U16 data type.
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"It’s the questions that drive us.”
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Message 6 of 6
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