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App Notes

Software & Driver

 

2.6.5 - Signal Range

Following are figures showing the approximate signal range of the U6 analog inputs.  "Input Common-Mode Voltage" or Vcm is (Vpos + Vneg)/2.

Keep in mind that the voltage of any input compared to GND should be within the Vm+ and Vm- rails by at least 1.5 volts, so if Vm is the typical ±13 volts, the signals should be within ±11.5 volts compared to GND.

Example #1:  Say a differential signal is measured where Vpos is 10.05 volts compared to GND and Vneg is 9.95 volts compared to ground, and G=100.  That means Vcm=10.0 volts, Vdiff=0.1 volts, and the expected Vout=10.0 volts.  Figures for G=10 and G=100 are not available, but Vcm=10.0 volts and Vout=10.0 volts is not valid at G=1 or G=1000, so is certainly not valid for gains in between.

Example #2:  Say a differential signal is measured where Vpos is 15.0 volts compared to GND and Vneg is 14.0 volts compared to ground, and G=1.  That means Vcm=14.5 volts, Vdiff=1.0 volts, and the expected Vout=1.0 volts.  The voltage of each input compared to GND is too high, so this would not work at all.

Example #3:  Say a single-ended signal is measured where Vpos is 10.0 volts compared to GND and G=1.  That means Vcm=5.0 volts, Vdiff=10.0 volts, and the expected Vout=10.0 volts.  This is fine according to the figure below.

 

 

2 comments

Does U6 support auto-ranging feature so that as per input analog signal it shall adjust the range if input analog signal varies and if suppose a range at a gain cannot measure it then it shall adjust accordingly?

Say your signal varies from 0-9 volts.  If you want to implement auto-ranging in your software, make your own analog input read function that starts by reading it using the +/-10V range.  If that initial reading is <1V, then grab a second reading using either the +/-1V,  +/-0.1V, or +/-0.01V range (depending on the value of the initial reading), and if that second reading looks good return that rather than the initial reading.  That is exactly how autoranging would work if implemented in firmware.