Automation test System - Switching

[sakthi11_4]

Hi 

     I am in the process of developing an Automation Test System to monitor the Continuity, Resistances and Capacitances from 12 DUT's. The DUT's are Printed circuit boards containing IC's, Resistors and capacitors and the boards will NOT be  Powered on while testing. There are 72 resistances and 72 capacitances to be measured. The test solution I have come up with now has a PXI 1033 chassis, NI PXI 4072 DMM, NI PXI 2575 Multiplxer and NI PXI 2530B Multiplexer.I have a couple of questions.

Test System : The DUT's will be put in the burn in oven and they ll be tested over a period of 6 months. The Automation system should be able to measure all the necessary parameters and log the data. 

1)  I would like to know how to introduce delay between the scanning cycles(Say that I have scanned 150 channels and measured all the parameters using 4072 DMM and if I want to introduce a delay(5-15mins delay) before the start of the next scanning  cycle ). How do I accomplish this in Labview ? As the Multimeter can monitor only one parameter at a time, I have developed 2 VI's one to measure resistance and another to measure capacitane using Semaphores. This is to ensure that the resistance VI is in the idle state when Capacitance VI runs and vice versa .Please let me know whether this method would work out ?

2) The Capcitances on the DUT's are 2nF and how do I compensate the parasitic capacitances that might come into the picture . I have gone through an article in NI website and learned that Multiplexer configuration is not ideal for Low capacitance measurements. If so, which topology should I consider for switching ? Or else if I want to go ahead with the Multiplexer configuration mentioned above, how do I compensate the parasitic capacitance ? 

Can I disconnect all the DUT's from the Automation Test System , measure the capacitance on each channel and use them for compensation?

Looking forward to your suggestions

Thanks in advance, 

Sakthivel.K

[Frank-L · Accepted solution]

1)  I would like to know how to introduce delay between the scanning cycles(Say that I have scanned 150 channels and measured all the parameters using 4072 DMM and if I want to introduce a delay(5-15mins delay) before the start of the next scanning  cycle ). How do I accomplish this in Labview ? As the Multimeter can monitor only one parameter at a time, I have developed 2 VI's one to measure resistance and another to measure capacitance using Semaphores. This is to ensure that the resistance VI is in the idle state when Capacitance VI runs and vice versa. Please let me know whether this method would work out ?

To introduce a delay between scanning cycles you can always set up your scan list to be finite and stop the measurement and the switch scanning after it has finished X channels. Then you can change measurement types for the capacitance measurements. You can then add a delay and then restart the measurement / scanning sequence again every Y minutes.

2) The Capcitances on the DUT's are 2nF and how do I compensate the parasitic capacitances that might come into the picture . I have gone through an article in NI website and learned that Multiplexer configuration is not ideal for Low capacitance measurements. If so, which topology should I consider for switching ? Or else if I want to go ahead with the Multiplexer configuration mentioned above, how do I compensate the parasitic capacitance ? 

Can I disconnect all the DUT's from the Automation Test System , measure the capacitance on each channel and use them for compensation?

Best bet is to use a different topology if the capacitance in Figure 2 is an issue. But....

From the same link:

A proper Open compensation for C₁ requires C₂ and C₃ to be connected. This would require the MUX to open channel 1 and close channels 2 and 3.  The MUX topology does not allow such a configuration state, and therefore the topology shouldn’t be used when accurate low-level Open compensation is required.

You could maybe do open compensation as described above with relay control as the 2575 is a latching relay and all relays can be closed at once using relay control. This adds additional time and complexity of the system