Switch Software management

Question

Hi,
      I am in the process of developing a System to monitor the components on the Printed circuit boards in oven,It s a basically a failure analysis of the components such as C's,Resistors and Capacitors. 
The following is an overview of my test system 
The test system should monitor the components on the PCB 1 year.
I would like to measure the Resistances and Capacitances using an LCR meter to identify the failure. Failure of the Resistor is identified with a Open circuit and a failure of the Capacitor is identifed with a short circuit/open circuit.I have 420 capacitances to be measured and I would like to automate the measurement using NI Multiplexers.
I have to monitor the first Capacitance (C1) for 3 mins ( which would be connected to the first input of the multiplexer) , followed by second for 3 mins and so on. Once all the 420 capacitances are monitored , the loop should start again from Capacitance C1.  I would like to know how to program the NI 's switches. Could someone please suggest me how to go ahead with this.? Is Labview good enough to automate the switches or should I go ahead with a switch management software ? Can you please explain in detail as am a newbie to Labview ?  Looking forward to your response. Thanks in advance 
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Answer 1

Hello there, 2nF approaches the territory where we need to consider the parasitic capacitance in the cabling/modules/etc.  For example, the multi-conductor LFH-200 cable that plugs into the PXI-2575 specifies 25pF/ft nominal parasitic capacitance with a single-ended signal, versus 15pF/ft nominal with a 2-wire signal. There's also internal capacitance from the switch, your test harness (anything that plugs into the LFH-200 cabling), etc.  With a 1-wire system, all DUT capacitor minus terminals are connected together all the time, which means you have a bunch of additional coupling locations for additional stray capacitance... wherever you have a stray path from any of the minus leads back to the particular channel under test.  For example, you could have coupling back through each capacitor's power supply back through the DUT's power supply and then into your measurement, etc.  With a 2-wire system, both the plus and minus are switched, which greatly reduces the number of venues for stray parasitic capacitance.  You might be able to get away with a 1-wire system, but my concern is with 420 channels your parasitic capacitance could approach your DUT capacitance.  If the parasitics are constant, you could compensate out the error, but I still recommend a 2-wire solution. 
NI HW definitely allows synchronization between DMM/Switch using external triggering, but in your case I recommend just using SW API calls: "switch: connect CHn" "dmm: take measurement y times" "switch: connect CHn+1" etc.  Synchronization is a method to measure as fast as possible, whereas you're taking measurements over a period of hours with a required period for each DUT... with HW synchronization, you can't implement a "wait t seconds" (unless you used additional external hardware, e.g. 555 timer to add delay, but this isn't practical when there's a perfectly good SW API). 
Note that if you're not comfortable with LabVIEW programming, but do know text-based programming, NI-Switch has a full-featured C++ API.  NI-Switch includes numerous examples in both LabVIEW and C++, and of course the community here can offer tips/hints/advice if you run into coding trouble. 
-John Sullivan
Analog Engineer