PXI-2567 fuse

[Bob_Albern]

I regularly blow the 5V fuse on my PXI-2567 boards (I only use the 5V supply). The card is wired through a Virginia Panel G12 interface to a custom load board. The fuse sometimes blows by simply changing test fixtures. The one time I paid close attention, the fuse was fine while I disabled and removed the current fixture, but then blew when I connected a new fixture to the interface. The fuse never blows during test operation so it's not an over current problem. I have verified that all relays are disabled when I change fixtures. One possibility is there is a current spike when I connect the new fixture, but it would have to be a lot of static buildup to cause this. (I am in nice dry Colorado.) Has anyone had experience with this and is there a recommended decoupling scheme to prevent the current spike? How about using fuses that are not slow blow? Any other ideas of why the fuse is blowing?

Thanks,

Bob

[Sandra_T]

Hello Bob,

I see that you are using our PXI-2567 with a G12 interface from Virginia Panel. Is there anything on the custom load board that could cause a current spike (capacitor, voltage/current source)?  How did you verify that the relays were disengaged? Do you have a second PXI-2567 to test with?

Regards,
  Sandra T.

Applications Engineer | National Instruments

[Bob_Albern]

Sandra,

I have two testers and multiple load boards / VP fixtures. Although I haven't tried every combination and the fuse doesn't blow every time I connect a fixture, it has happened with multiple fixtures on both testers.

I have verify in MAX that all relays are open before changing a fixture and the fuse blew.

Bob

[Sandra_T]

Hello Bob,

Is there anything in your test fixture that will be driving a large current as you plug in your device?
Perhaps consider some sort of external circuitry that will allow you to deal with spikes and overvoltages.

Do you have any additional insight on what in your test figure that cause this issue?

Sandra T.

Applications Engineer | National Instruments

[Bob_Albern]

It has been six months and we have implemented strict ESD procedures while swapping test fixtures and fuses continue to blow about every 10 swaps. We currently use the Littelfuse 451002 Very Fast Blow fuse as specified for the board. This has a 2A current limit, and a  I^2T rating of 0.5. What would be the implications if we changed to either a [ 54102.5 2.5A limit, I^2T 1.0 fuse ] or a [ 542002 Slow Blow 2.0A limit, I^2T 8.0 fuse ]? A 16x jump in power rating seems a bit extreme but the 2x may do the trick. Would a 2.5A current limit put the 5V supply circuit on the 2567 at risk? We rarely switch more than half a dozen relays at a time so our applications never come close to the 2A limit. The board is out of warranty so I don't think that is an issue.

Bob

[Nathan_R]

Hi Bob,

So you are using a PXI-2567 that is connected to a Virginia Panels G12. I’m assuming the relays the 2567 is controlling are in the test fixture. I’d be happy to help you narrow this problem down. I have some questions about your test setup that may help us figure out what is causing the fuse to blow.

1.     What relays are you using with the 2567?

2.     Are the 2567 all channels open every time you switch test fixtures?

3.     Do you have any kind of capacitive load on the 5 volt line in your test fixtures? If you do, this could cause a current spike on connection that is blowing the fuse. A capacitive load will draw a lot of current from a dc source until the load is charged. This could also be why the fuse blows on connection of a new test fixture and doesn’t blow when you remove a test fixture. If a specific test fixture is not blowing the fuse every time it may be that the initial current draw is just enough to sometimes blow the fuse but not always.

4.     Is there any fixture that has never blown the fuse? If so does is that fixture’s relays wired differently than the multiple fixtures that have blown fuses?

Any additional information you can give to help narrow down the cause of the problem will be helpful.

Thanks,

[Bob_Albern]

Nathan,

Here are my replies to your questions.

1.     What relays are you using with the 2567? >

2.     Are the 2567 all channels open every time you switch test fixtures?

3.     Do you have any kind of capacitive load on the 5 volt line in your test fixtures? If you do, this could cause a current spike on connection that is blowing the fuse. A capacitive load will draw a lot of current from a dc source until the load is charged. This could also be why the fuse blows on connection of a new test fixture and doesn’t blow when you remove a test fixture. If a specific test fixture is not blowing the fuse every time it may be that the initial current draw is just enough to sometimes blow the fuse but not always.

4.     Is there any fixture that has never blown the fuse? If so does is that fixture’s relays wired differently than the multiple fixtures that have blown fuses?

[Bob_Albern]

Nathan,

Here are my replies to your questions.

1.     What relays are you using with the 2567?   

>> Various Pickering relays, all with built in diode protection on the coils.

2.     Are the 2567 all channels open every time you switch test fixtures?   

>> This is one of our SW design rules but I can't guarantee that all relays are always open on all fixtures when the fixture is swapped. On the last two boards I designed I inserted a relay in the +5V line itself. This relay is the only one hardwired to +5V. All of the other relays on the board are connected when this relay is enabled when testing begins. Even with this configuration, the +5V fuse will occasionally blow.

3.     Do you have any kind of capacitive load on the 5 volt line in your test fixtures? If you do, this could cause a current spike on connection that is blowing the fuse. A capacitive load will draw a lot of current from a dc source until the load is charged. This could also be why the fuse blows on connection of a new test fixture and doesn’t blow when you remove a test fixture. If a specific test fixture is not blowing the fuse every time it may be that the initial current draw is just enough to sometimes blow the fuse but not always.

>> No caps or other circuitry is attached to the +5. Only relays are powered by the 2567 +5V.

4.     Is there any fixture that has never blown the fuse? If so does is that fixture’s relays wired differently than the multiple fixtures that have blown fuses?

>> Not that I know of although in the past we had not been keeping track. I am collecting this data now but don't have enough occurrences to draw any conclusions.

[Nathan_R]

Hey Bob,

I would keep tracking which fixtures cause the fuse to blow and see if any specific fixture is the more or less likely to blow the fuse. From there we can look at how they are wired for a possible cause. You could also try simplifying the problem by making a test fixture with just one relay wired in it and see if connecting and disconnecting it still causes the fuse to blow. I would also make sure that the relays are all open when the test fixtures are changed out.

Thanks,