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ADC-20 differential inputs

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ADC-20 differential inputs

Postby Guest » Thu Aug 23, 2007 2:24 pm

I have just purchased an ADC-20 and terminal board.
I have an input of 48V DC and would like to log it.
I have purchased a 9530ohm (Ra) and a 499ohm (rb) resistor.
Does this sound correct?
The description for Ra says that the track underneath the resistor needs to be cut. (on my ADC-11, this was obvious), but where is it? There are two blue tracks running through the Ra label, but I have been unable to scrape this away.
I have been trying using a differential input, with Rb wired to the -5v on the right hand side (RHS).

Also, then when I try and use the next differential channel, it is affect by the reading of the first.

Finally, if I just want to monitor voltage, where should Rb be wired to on the RHS? AG, -5v or +5v. No success so far.

Many thanks

James McIntyre
Guest
 

Postby picojohn » Fri Aug 24, 2007 11:37 am

Hello James,

The resistor values you have chosen will give an ADC input of 2.39V for 48V input to the divider, assuming that you have taken the source resistance into consideration as explained in the user guide.

The track to be cut is located as described in the user manual, i.e the raised area under the silk screen printing for the component location, 'Ra'. It may be easier to carefully cut the gold-plated part of the track a mm or so before the solder pad.

The non-signal end of 'Rb' should be connected to 'AG' for 'single-ended' measurement.

If you are uncertain, then you could connect the divider at the screw terminals by placing 'Rb' between the input terminal and 'AG', and, connect 'Ra' in series with your 48V signal and the input terminal. The input signal ground should be connected to AG.

Regards
John
picojohn
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