ADC-16 Differential Measurements

Neil · Post by **Neil** » Wed Oct 29, 2008 5:01 pm

I have been trying to make measurements on a device with a 0-1Volt output, but referenced to 5V not ground. In other words my signal goes between 5Volts and 6Volts. The ADC-16 gives me strange results with the input in question affecting all the other channels.

Is this outside the acceptable range for the ADC-16? How else could I use the logger to measure this input?

Thanks,

Neil

Robin · Post by **Robin** » Thu Oct 30, 2008 9:15 am

Hi Neil

Which pins is your input connected to? The pin connections are as follows:

1 Channel 1 (differential pair with pin 2)
2 Channel 2
3 Channel 3 (differential pair with pin 4)
4 Channel 4
5 Channel 5 (differential pair with pin 6)
6 Channel 6
7 Channel 7 (differential pair with pin 8 )
8 Channel 8
9 - 11 Reserved for future expansion
12 Reference Output
14 - 25 Signal Ground (Computer 0 V)

Is your input connected to a differential pair e.g. pin 1 and 2?

Robin

Neil · Post by **Neil** » Thu Oct 30, 2008 9:27 am

I have my sensor connected across pins 1 and 2. On the PC, the picologger Channel 1 is set up with the differential input ticked.

Neil

Robin · Post by **Robin** » Thu Oct 30, 2008 9:37 am

Neil

I should have noticed, but you are operating outside of the input range of the logger.

Your common-mode voltage should be within the input range of the logger i.e +/- 2.5 V..

You could reduce your input using a potentiometer or you can connect your 5 V to the ground as long as whatever you are measuring is floating.

I hope this helps

Robin

Neil · Post by **Neil** » Thu Oct 30, 2008 4:22 pm

Thanks for the help. I will try your suggestions.

Neil