Original question:
Dear sir,
We have to measure +110V DC & -110V DC to Earth Continuity Ok/Not OK?
For this we need reference Idea how to read +110V DC to Earth and Earth to -110V DC through Microcontroller ADC (If need to add OP-Amps no problem)
If possable above 20K resistance or Bellow 20K resistance also OK for us.
Please guid us
nsprateep@sirveen.com
Hi Sridhar,
Sincere apologies about the delay; it looks like this post didn't get sorted into an owner correctly on the TI side.
A microcontroller ADC input pin will typically have an input range of 0V to 2.5V, 3.0V, or 3.3V.
For signal that is 0 to 110V you might be able to get it into the lower voltage range strictly by using a voltage divider, but this has a variety of caveats. For more information about this method, see the following app. note:
However, if you want to sense a signal that is 0 to -110V or -110V to +110V you are definitely going to need an op-amp (or possibly an instrumentation amplifier or isolated amplifier).
If the ground for the -110V to +110V signal is the same as the microcontroller, then you can just go ahead and use a voltage divider to scale the voltage down followed by an op-amp to buffer the signal and add offset to bring the signal into range of the ADC. I can help you with this further if needed. If the ground for the -110V to +110V signal is possibly floating with respect to the microcontroller, then I think you may need an isolated amplifier (or maybe instrumentation amplifier). For instance, have a look at the typical application information in the AMC1311 datasheet. Does this seem like roughly what you want?:
