Digital Multimeters (DMMs) and Precision DC Sources

cancel
Showing results for 
Search instead for 
Did you mean: 

Continuity testing and NI 4072 DMM

I am trying to create a continuity test which looks for opens and shorts and I am looking for advice to try and speed things up, if possible.

The DMM I am using is a NI 4072 and I am also using a  PXI 128x2 Matrix Module from Pickeringtest to do the switching between test points.

Now I know the pcb board I am testing does not have 128 test points but for testing my code I thought I would do it all anyway. Running my test takes 7 minutes!

 

Now lets say for arguments sake that I only had 64 test points which is probably not far from the truth, that is like 3 - 3.5 minuts.

 

Questions,
For the setup I have, does this time sound about right and it is infact hardware limitation?

Or

Is there someting I can do/change etc to speed this up.

 

I have the DMM set like this

 

AutoZero is set to ON

Power Line Frequency is set to 50

DMM is set to AutoRange

Measurement type is Resistance

Resolution is 6.5 Digits

 

the code is written in c# .Net but its straight forward in what I am doing.

                       for (int i = 1; i < 127; i++)
                        {
                            for (int j = i + 1; j < 128; j++)
                            {
                                // Set IO
                                Controller.IO.SetCrossPoint(i, 1);
                                Controller.IO.SetCrossPoint(j, 2);

                                var reading = dmm.Measurement.Read();
                               

                                // Reset IO
                                Controller.IO.ReSetCrossPoint(i, 1);
                                Controller.IO.ReSetCrossPoint(j, 2);
                            }
                        }

 

Basically I am opening a connecion to 2 test points, taking a reading, closing the 2 test points and repeating.

 

I understand that the speed in which the Matrix module operates can affect this, the DMM resolution and the range but we have a 10 year old ATE that seems to be able to do a continuity test in a second. I questioned this so I started removing pins from the bed of nails and hey ho it found open circuits.

0 Kudos
Message 1 of 10
(7,392 Views)
High speed short/open testing is done with digital i/o where all of the pins are tested at once and only a couple of patterns are required.
0 Kudos
Message 2 of 10
(7,385 Views)

Have you done any profiling to determine where the time is being spent (DMM vs Switch)?

You are configuring your DMM for a very high precision measurement (6.5 digits) in which you have no idea of the range (Auto-Range). First one means the measurement is pretty slow, the second one means the DMM is going to do a first quick measurement to determine what range to use, then switch range, then do the high precision measurement.

 

For your needs, selecting a specific range and lowering to 3.5 digits of precision should speed things up considerably and still be a good enough measurement.

 

You will see an even bigger improvement in performance if you use multi-point, since the DMM doesn't need different configuration between measurements. Since you are using a Pickering switch, not one of NI's, you cannot have the two devices handshake over PXI trigger lines (that would be even faster). But you can use a software trigger to trigger the DMM after you have programmatically changed the setting on the switch.

 

Hope this helps!

Marcos Kirsch
Chief Software Engineer
NI Driver Software
0 Kudos
Message 3 of 10
(7,382 Views)

Dennis, Sorry if this sounds dumb but could you explain a little more in what you mean?

0 Kudos
Message 4 of 10
(7,380 Views)

I just modified the program so I only look at the Test pins on the board, Set the DDM Range to 100 Ohms and the precision to 3.5digits.

 

This dropped the time down to 1.30 mins which is a big improvement, but would love to get it down even more.

 

I'm a little confused on this part
Since you are using a Pickering switch, not one of NI's, you cannot have the two devices handshake over PXI trigger lines (that would be even faster). But you can use a software trigger to trigger the DMM after you have programmatically changed the setting on the switch.

 

What do you mean by two devices handshaking over PXI trigger lines?
and
I thought requesting a read from DMM is doing a software trigger?

 

Thanks for all the help and sorry for the 101 questions, I am the software guy on this project and the electronics guy who built the test jig left halfway through the project so I don't have him to fire questions at haha

0 Kudos
Message 5 of 10
(7,379 Views)

What do you mean by two devices handshaking over PXI trigger lines?

On the DMM side: You can configure the DMM for multi-point measurements. You can also use a trigger, that is a digital signal to tell the DMM to measure the next point. The DMM will emit an event, another digital signal when each point is done.

On the switch side: NI switches support scanninga pre-programmed sequence of connections. You can configure the switch to use hardware triggers as well.

You can use NI-SWITCH and NI-DMM to route these triggers to each other via the PXI Trigger Lines in the backplane of the chassis, so they advance in tandem, hardware timed, as fast as possible. This is much faster than the software-timed aproach you are using. Our drivers come with examples that show you how to do this.

Marcos Kirsch
Chief Software Engineer
NI Driver Software
0 Kudos
Message 6 of 10
(7,372 Views)

Thanks for that info, I will have a closer look.

0 Kudos
Message 7 of 10
(7,369 Views)

I thought requesting a read from DMM is doing a software trigger?

 

Since you are not changing configuration between measurements, you will see a performance improvement by configuring the DMM for multipoint measurements, calling Initiate, and then using a software trigger for triggering each point within your multi-point measurement. We install examples with our driver that can help you figure it out.

Marcos Kirsch
Chief Software Engineer
NI Driver Software
0 Kudos
Message 8 of 10
(7,368 Views)
Digital testing for shorts and opens is trivial. You apply zeroes and ones at one end and look for the same pattern at the other. If you see a zero when you expect a one, two lines are shorted. For 8 lines, you need to apply F0x, AAx, and 55x. Should take fractions of a second.
0 Kudos
Message 9 of 10
(7,340 Views)

Thanks for that Dennis, I did some reading on a similar post where you also explained about using Digital testing and will look into this more 🙂

As you have some experiance with building testers I didn't know if you had a moment to check out my other question I posted.

0 Kudos
Message 10 of 10
(7,332 Views)