Multi sample DAQ for resistance measurements

[EngineeringEE]

Hello All, 

I am trying to create a test set up to monitor the resistance drop for some interdigitated electrodes.  I am conducting an accelerated lifetime material study for packaging materials of implantable devices.  I am coating PCBs each with 10 devices with the materials and soak testing.  The resistance is monitored.  When the resistance drops to a certain point the packaging is said to have failed.  I have 3 temperatures I am testing at (45, 60, 85 C) each with 60 devices (6 PCBs).  I am currently using an NI USB 5133 DAQ and I also have a NI 6024E DAQ card.  My idea is to make a program to switch from one device to another every 10 seconds.  The point is to monitor the resistance until it reaches a certain point over a long period of time (since the packaging is suppose to last for more than 2 weeks). 

The other idea is to create a set up utilizing a multiplexer.  The multiplexer will simply serve as a switch for the resistance reading while the DAQ will gather the reading.  Labview will control the DAQ and put the data into a nice Excel Spreadsheett.  All suggestions are welcomed!!

Thank you for your help!!!

S.L.

[Ali M]

Hello EngineeringEE,

As per the hardware you provided, a point of concern was the number of devices on each PCB you wish to measure. Since you will be monitoring resistance, you will require a current source supplied to each device in order for you to read the voltage. If you already have a method in place for doing so, please clarify/provide more details. Otherwise, I would recommend looking into a solution using an NI Switch and NI Digital Multimeter (NI DMMs offer current excitation) to acquire measurements from multiple devices/PCB boards. A plausible solution would involve Synchronous Scanning, where the NI DMM would take a measurement and generate a digital pulse-Measurement Complete (MC). When the switch receives this digital pulse, it advances to the next entry in its scan list. The DMM would then take the next measurement, after a programmed time interval. This example is also offered with the driver and named Switch Scanning with DMM - Synchronous.VI. If you have any questions, feel free to post an update.

Best regards,

Ali M

Applications Engineer

National Instruments

[EngineeringEE]

Hello Ali,

Attached is a simple schematic of what I plan to use as a test set up.  To solve the issue of switching from one device to the next, I developed a board with four 32 to 1 multiplexers all leading to one 4 to 1 mux. which has it's output to the DAQ.  I want my NI USB 5133 DAQ to take a resistance (current or voltage) measurement every hour from all of the 100 devices monitored.  I will place a voltage divider in between my 4 to 1 and DAQ. 

My main problem is programming LABVIEW to syncronize my Arduino's switching time with the time the DAQ takes the measurement.  Is there a way to have labview communicate to the ARDUINO to let it know when to switch and tell the DAQ when to take the measurement?  Also, I want the DAQ to take the measurement and record it into an excel spreadsheet with the number of the device (1-100) it took the reading from.  Is this possible?  Are there examples on how to get this DAQ to measure a voltage or current?  I currently have NI SCOPE installed but when I go to the functions palette there is no VI for NI SCOPE EXPRESS.  How can I retrieve this VI or download the software for it?  I am new fairly new to Labview and would appreciate any thoughts or suggestions concerning this set up.  I can not purchase any more equipment.  I am using what is in house.

Thank you for your help,

S.L. 

[TimmTheEnchanter]

Hi EngineeringEE,

I"ll do my best to try to answer your questions.

It's my understanding that an Arduino board has a serial port interface.  In that case, you could communicate to it using LabVIEW VISA commands.  Searching around Google for "Arduino LabVIEW" crops up a ton of results and examples, some of them on the NI Discussion Forums.

If you're looking for generic VISA examples, you can look at examples for NI-VISA in Help>>Find Examples... (the Example Finder comes up) and look in Hardware Input and Output>>VISA.  VISA is a driver that calls into many port interfaces, including serial, for instrument control.  It's designed to be generic, so similar programming can be applied using any interface, including Serial, GPIB, USB, etc.  

Based on your diagram, synchronizing your Arduino to your LabVIEW program is more a question of "how you want to do it" and how it relates to your LabVIEW program using these VISA calls.  

If we think outside of your diagram, you could possibly physically share a few wires between your Arduino and DAQ device, you could import and export signals that could also synchronize.  Advantage: to this is that you could run your program with more determinism--disadvantage: you need to have a good amount of experience with LabVIEW and DAQmx programming, the right cables and connections, etc. to pull it off.  Also, I would expect this would require the Arduino to be programmed with interrupts or at least continuous polling.  Someone on an Arduino-specific discussion forum will have more insight into what the Arduino is capable of..

For writing values into a spreadsheet, you can see more examples in the Example Finder by looking in Fundamentals>>File Input and Output (more information on specifically what you want to do with File I/O can be better answered on the LabVIEW forum).  Similarly--depending on if you want to use the 5133 Scope to measure values, or if you want to use your DAQ device to measure values, you can look in these spots for examples:

Scopes: Hardware Input and Output>>Modulare Instruments>>NI-Scope

DAQ: Hardware Input and Output>>DAQmx>>Analog Measurements

"NI-Scope Express" is kinda the equivalent of the "DAQ Assistant" VI.  It should be installed with the driver, which you can download the most recent version for on ni.com/drivers (type in "scope" to find the hits).  If you're not seeing this VI, it could either be that the driver didn't install it correctly, or you need to upgrade to a more recent version of the driver.

I hope these resources help.

Regards,

Andrew

[EngineeringEE]

Hello Andrew,

I have an update on my situation.  I now have found a NI PXI-1042 8 Slot chassis.  In it I have a NI PXI-6527 connected to a NI SCB-100 shielded connector block.  If I create a voltage divider or provide an voltage source, can I program labview to measure the resistance with the PXI 6527?  I am running Labview 7.0 EXPRESS on my PXI 8186 which is also in the chassis.  I tried to use DAQ assist but it is not allowing me to use the PXI 6527.  How can I read a measurement from the 6527?  Is there an example that does this?

Thank you for your help!!!

[EngineeringEE]

Sorry just one more question: How can I make labview switch the inputs on my SCB100??

Thank you!

[TimmTheEnchanter]

Hi EngineeringEE,

I am not sure what your intended setup is with the 6527 device, but it is a digital i/o device.  I don't see any way to take resistance measurements with it.  Did you meant to say you have a device with analog inputs that you'd like to use to take resistance measurements?

Also, I'm not sure what you mean by switching inputs on the SCB100.  Since the SCB100 is only a breakout board, there is no way to configure it or switch inputs on that device specifically.  The channels for the 6527 are accessed as data in LabVIEW, and you can programmatically determine where your data flows (that is, how you manipulate it or compute it) but it will always come from the same channel so long as the wires connecting to the SCB100 are configured the same way.

If you meant to talk about a multifunction DAQ device, such as a 62xx or 63xx device, you can see the I/O connections you need to make for your task using Connection Diagrams.

Regards,

Andrew 

[EngineeringEE]

Hi Andrew,

Sorry for the confusion.  I would like to measure voltage from 100 devices with the PXI 6527.  So from my understanding there are 100 input connectors on the SCB-100 labeled 1 to 100.  My devices #1 to #100 will be connected to the connectors #1 to #100 on the SCB respectively.  Can I tell my NI 6527 to take a voltage measurement from connector #1 first, then connector #2 second etc. until a voltage has been measured from all 100 devices?  Can I use Labview to control my 6527 in this fashion?  So, first I need to know if this is even possible.  Then, I will ask the next question on how to get LABVIEW to make the 6527 take a voltage measurement, and how to tell the 6527 to take a measurement from each connector.

Thank you and sorry again.  I am still learning labview, and am really not that knowledgable of DAQ.

S.L.

[TimmTheEnchanter]

Hi S.L.

This 6527 is a digital i/o board.  You will not be able to take voltage measurements with it without external hardware, and by extension, you won't be able to take resistance measurements.  If you are only trying to monitor on/off states (if that is what you're trying to measure when you say "voltage measurements") then you can do this with the 6527 so long as the on/off states correlate with TTL logic, or some other logic level this board supports.

However, even then you will not get 100 channels from this device.  The SCB-100 is a 100-pin breakout board, but that does not mean you will be able to measure 100 different signals.  As you can see from Fig. 3-2 (p. 3-4) of the 6527 User Manual, the pins break out as one positive, one negative, because this device is ch-ch isolated (no common ground).  Also, half of these pins (24) are dedicated input, half (the other 24) are dedicated output, as you can see per the Specifications on the 6527 product page. 

Honestly, your best shot for getting a setup that allows you to do what you're trying to do is to call up National Instruments and asked to speak with your account manager (technical sales representative).  He can help you get started with finding the right hardware for this application.  Also, it would definitely benefit you to take some classes to learn how to use LabVIEW and other NI products.  There are some online resources, but if you're serious about understanding how to use your hardware, signing up for a class will likely be more beneficial.  Please speak with your account manager about those options as well, as he can better direct you toward what you need.

Finally, just so we're oriented in the right direction--a DMM device with a switch device would be much more likely to suit your needs. Read through these links for help in getting started with those.  Also, there is this: How To Reduce Errors When Switching Low Resistances

Regards,

Andrew