Hi All,
I'm using the 2 analog inputs in HV mode and capturing the results using the acquire application.
Am I correct in understanding that the voltage per bit of the ADC is calculated as follows:
HV mode - input is max +/- 20V == 40V
40V / 16384 = 2.44mV per bit
Therefore, an average voltage captured by acquire of 291 is:
291 x 2.44mV = 710mV
The problem I'm having is that the voltage I am measuring is actually 1.729V, not 710mV, so I must be making a calculation error or misunderstand the conversion the RP is making on my analog input.
Thanks in advance for any help, Stuart
Converting raw acquire results into a voltage
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Re: Converting raw acquire results into a voltage
Hi,
You have correct calculation, so for HV setting
u = (ADC * 40 ) / 16384 [ V ]
and for LV setting
u = (ADC * 2 ) / 16384 [ V ]
I am not sure what you mean with “ acquire of 291 “
Regards, Zumy
You have correct calculation, so for HV setting
u = (ADC * 40 ) / 16384 [ V ]
and for LV setting
u = (ADC * 2 ) / 16384 [ V ]
I am not sure what you mean with “ acquire of 291 “
Regards, Zumy
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Re: Converting raw acquire results into a voltage
Hi Zumy,
Thanks for your reply. Unfortunately, your calculations don't seem to work correctly.
For example, the acquire application gives me an output of "3650", which I know to be about 0.48V because my multimeter says it is 0.48V and the RP Scope application gives me an average output voltage of 0.48V. This is for a LV input on the AFE.
So, according to the calculation, for a raw ADC value of "3650":
(3650 x 2) / 16384 = 0.446V - which is not 0.48V
OK, perhaps I didn't factor in calibration - my ch1 calibration factor value is 78:
((3650 + 78) x 2) / 16384 = 0.455V - which is still not 0.48V
So why are my calculations consistently ~5% less than the real voltage being applied to the AFE?
Something simply doesn't make any sense.
Thanks, Stuart
Thanks for your reply. Unfortunately, your calculations don't seem to work correctly.
For example, the acquire application gives me an output of "3650", which I know to be about 0.48V because my multimeter says it is 0.48V and the RP Scope application gives me an average output voltage of 0.48V. This is for a LV input on the AFE.
So, according to the calculation, for a raw ADC value of "3650":
(3650 x 2) / 16384 = 0.446V - which is not 0.48V
OK, perhaps I didn't factor in calibration - my ch1 calibration factor value is 78:
((3650 + 78) x 2) / 16384 = 0.455V - which is still not 0.48V
So why are my calculations consistently ~5% less than the real voltage being applied to the AFE?
Something simply doesn't make any sense.
Thanks, Stuart
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Re: Converting raw acquire results into a voltage
Have you had a look at this thread from the old forum ? It contains some info on the conversion, as well as some pointers to code that does the conversion in the apps.
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