DT9818 Dynamic Resolution?

[TM178]

Hi, I am curious if DT9818 has dynamic resolution. The DAQ specifies a fixed resolution of 16-bits. However, this DAQ also offers different input ranges & gains for its analog channels (page73), see excerpt below:

Per this recommendation, two of our analog input channels are set to have gain 8 as the signal we are reading comes nowhere near 1.25V (less than 10mV).

My question is, especially based on the comment from the excerpt ("... which provides best sampling accuracy for that channel"), is the resolution for our gain 8 channels 0.15mV/bit or 0.019mV/bit?

 

Thanks for your help, I couldn't find anything explicit about this in the data sheet.

 

 

[Fausto]

Hello @TM178.

The DT9818 uses one 16-bit A/D converter for its analog input subsystem.  However, since the DT9818 (as any other daq module) has other components and circuitry in the design, the 'effective number of bits' (ENOB) is 14.1 bits; as reported on Table 28 on page 123 in the DT9818 User's Manual.  

https://www.mccdaq.com/PDFs/Manuals/UM9818.pdf

Your calculations would use 14.1 bits and a total range of 2.5 V (for the +/-1.25 V input range).

17560 discrete points & a 2.5 V range

(2.5 V) / (17560) = 1.4E-4 V/bit

For an acquisition, definitely use the smallest input range available on the DT9818 for your voltage level.

Regards,

Fausto