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RobH
User
Posts: 6
Joined: Wed Nov 01, 2006 12:05 pm

Hi

Background:
I'm using and ADC-16 to measure a voltage drop across a low value resistor (0.25 ohms). This resistor is in series along the return line from a product to its battery.

I use a calculated parameter to show the current, log that for around 1/2 an hour, then (using excel) integrate current over time intervals to get instantaneous charge, sum the charges and divide by total time to get average current. (Simple, eh?!?!)

Problem:
I need to measure the 'off' (or Standby) current of the product, typically nano-amps, but the drop across the resistor is not enough to be seen by the logger.

Attempted solutions:
A previous solution was to put the data-logger in series (instead of the low value resistor) but the impedance needs to be known. (Previously an ADC-42 was used, this is no longer available and attempts to measure the impedance of the adc-16 have yielded dubious results). I know itâ€™s about 1Mohm but I could do with a few decimal places on that.

Rob

RobH
User
Posts: 6
Joined: Wed Nov 01, 2006 12:05 pm
I should have pointed out that I need to know the impedance of my ADC-16, not any old generic value.

Thanks

RobH
User
Posts: 6
Joined: Wed Nov 01, 2006 12:05 pm
Ok, update for you, me, er... (ever get the feeling you're talking to yourself?)

I have used another multimeter (high quality) to measure the impedance of the ADC-16. It worked! (after a fashion).

The problem I have now is that the multimeter outputs 1.01V (as can be seen in the PicoLog software) to make the measurement, this means that I have measured the impedance of the logger's 1V range, does the ADC-16 have multiple ranges? Is it autoranging? (I would imagine so)

If this is the case I can "force" the ADC-16 into the appropriate range by placing a known (very) large resistor in series with the ADC-16 but this makes the measurement a little more... unstable, and it's hard to get an accurate reading.

I hope this simplifies the question, basically I need to know if the ADC-16 has multiple range, and if so, what are they?

Thanks

Rob

Michael
Posts: 656
Joined: Thu Jul 07, 2005 12:41 pm
Location: St Neots, Cambridgeshire
Hello Rob,

The input range is fixed at Â±2.5v, there is no autoranging included.

If you are writing your own software, you will find this information in the product manuals.

Best regards,
Michael
Michael - Tech Support
Pico Technology
Web Support Forum

RobH
User
Posts: 6
Joined: Wed Nov 01, 2006 12:05 pm
Perfect!