DC Stimulus

Discussion in 'General Electronics Chat' started by uriahsky, Jan 5, 2014.

  1. uriahsky

    Thread Starter Active Member

    Apr 27, 2009
    There is a piece of test gear made by ABI Electronics called a CM4000. It is an O-Scope with some other features. One of the features I am interested in is what they call Firm/Flex testing. They apply a 5VDC current controlled signal to what ever node you are testing and screen will readout the voltage and if the signal is encountering a firm or stiff reaction to the 5VDC or a Flexible response.

    One of the examples given is if your testing a resistor and you read 0 ohms across it this could be a short or an open somewhere else in the circuit. Using the 5VDC stimulus voltage can help you determine which one it is.

    I haven't seen this technique used on other test equipment in this way. Am I missing the obvious. Is there other test gear out there that does this kind of thing? The CM4000 is about $4000.00 and I don't want to spend that just to use this test feature. Would there be an easy way to add this to a standard DVM? I am aware of current probes and other ways to test for opens and shorts but it is this specific technique I am interested in.
  2. #12


    Nov 30, 2010
    Just use an LM317 and a 9 volt battery to make a constant current source of 10 ma and apply that to the "node of interest". If you don't want the float voltage to be about 8 volts, use a zener diode or an LED to waste some of the voltage.
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Are you sure you want to spend $4000 on this?