07-18-2007 04:21 AM - edited 07-18-2007 04:21 AM
Message Edited by andrew_JKTA on 07-18-2007 04:22 AM
07-18-2007 11:46 AM
With the typical DAQ board, you have a single A/D converter that is muxed between multiple connections. The A/D only measures voltage. In order to measure current, you have to add external shunt resistors to each channel. In order to measure resistance, you have to provide a current source. A DAQ board is often only DC coupled so to do AC coupling, you would have to provide some more external circuitry or remove the DC component in software. A DAQ board will return a series of voltage readings made over time and you might have to do other calculations in software. For example, determining the RMS voltage. A DAQ board will usually have a limited input range. It might be something like +/- 10 volts. In order to read higher voltages, you would again have to provide some external voltage dividers.
A DMM, will have usually have a single channel and all of the external circuitry you need for the DAQ board, will be internal to the DMM. A DMM's firmware will perform all of the necessary calculations to convert the voltage reading of it's A/D to amps, ohms, rms, etc. Because a DMM has only a single channel, in order to read multiple points, you need to provide some external switching. Because it only has a single channel, you cannot measure multiple points at the same time.
07-19-2007 10:27 AM
Thanks very much for the information
I have decided to use PCI-4070 for the measurements
Thanks again