DMM and switch systems

Question

I am trying to put together a system that is capable of measuring 48 current shunts that I would like to maintain isolation from the SCXI chassis ground.  I am considering using a PCI 4065 and an SCXI-1127 or 1128 switch module, 2 of one of them.  What I am unsure about is which type of switch I should use, the solid state or relay?  Also I am not sure how the termination of wires should be made.  Each shunt will have two wires coming from it.  Should these two wires from each shunt go into the switch module and are then all terminated at the DMM?  Is there a cleaner way to do this or is my assumption incorrect on the wiring strategy?
Is there a better solution?
Will the DMM provide results similar to a handheld DMM?  i.e. averaging the voltage level read. 
thanks in advance.   

Answer 1

Hi,
FET switches such as the SCXI-1128 will have a faster scan
rate and lower power requirements than mechanical relay switches such as the
SCXI-1127.  The advantage of using a mechanical
relay is the amount of current it can switch and carry.  You should base your decision on the specifications
of your input signal and how fast you will eventually need to scan through the
channels. 
The two wires from each shunt will connect to the terminal block (which will have inputs corresponding to the channels of your switch module) and the DMM will connect to the output of the switch
module (through the terminal block).  Scanning through the channels
will connect one channel to your output (DMM) at a time.  The Developer Zone articles: How to connect signals to the SCXI-1127 and How to connect signals to the SCXI-1128 describe the connections in detail.  The DMM will then average the voltage measurements
to provide a more accurate reading.
Best Regards
Hani R.
Applications Engineer
National Instruments