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Unread 19-02-2012, 22:59
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Potential DSC Damage

As I can't find this specification on the USFIRST-provided spec sheet (or a confirmation through forum searches), I'm turning to the CD community for a definitive answer to this question: Is the ground on the GPIO pins of the DSC 12V tolerant? Alternatively, will plugging in a 12V signal to the power or ground pins on the GPIO damage the DSC?

The reason I ask is because we've been having issues with an apparent short to our frame, which induces sudden motion upon providing power to the robot, but the short point is unidentifiable, and we suspect the damage lies in the DSC.

The current situation is as follows: Closing the circuit breaker (giving power to the PDB) will, on occasion, incur forward motion in a number of motors that persists for a few seconds. I know for sure that the motors on PWMs 1-3 and 6-7 are moving forwards; 4 and 8-10 have no connections, and 5 may be doing so (but is unconfirmed). Later testing only saw motion in a subset of these motors (which is undetermined).

The backstory: The sensors (details later in the post) were wired with +12V and GND to a 20A PDB, a 1K pullup across the 5V and signal, and the signal wire was mistakenly plugged into both the +5V and GND (at two different points).

The one common factor that we have confirmed is that this phenomenon only occurs when the signal from our conveyor sensors is plugged into the DSC (on the signal pins), in particular when one of them is activated. We are using Banner QS18VN6D sensors (the white signal line) for this purpose.

The camera and cRIO are isolated from the frame and we cannot identify any other potential shorting point.

Edit: Omitted detail: All 3 lights on the DSC are lit. The RSL has yet to be connected, so I can't describe its behavior.

We didn't get a chance today, but we plan to confirm tomorrow whether the point of failure is the DSC (if we can reproduce the issue) by cutting its power and unplugging the DB37. Until then, it would be great if someone could confirm our hypothesis.
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Last edited by slijin : 20-02-2012 at 00:32.
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Unread 19-02-2012, 23:41
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Re: Potential DSC Damage

I won't hazard a guess. I suggest you PM EricVanWyk and direct him to this thread. (Assuming he hasn't found it already.) He has some deep insider knowledge about the DSC and should be able to answer you quickly and authoritatively.
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Unread 19-02-2012, 23:41
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Re: Potential DSC Damage

it is definitely not a good idea to be dumping 12v into the sidecar. I would suggest you sink your power elsewhere, and use a transistor arrangement to connect the two pins (sig,gnd) so that there is no extraneous power on the sidecar.
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Unread 19-02-2012, 23:43
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Re: Potential DSC Damage

Quote:
Originally Posted by Kevin Sevcik View Post
I won't hazard a guess. I suggest you PM EricVanWyk and direct him to this thread. (Assuming he hasn't found it already.) He has some deep insider knowledge about the DSC and should be able to answer you quickly and authoritatively.
I've already done so

Nonetheless, I still wanted to put this out there for anyone else who's familiar with and knowledgeable enough about the DSC to respond.
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Unread 19-02-2012, 23:44
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Re: Potential DSC Damage

Quote:
Originally Posted by slijin View Post
As I can't find this specification on the USFIRST-provided spec sheet (or a confirmation through forum searches), I'm turning to the CD community for a definitive answer to this question: Is the ground on the GPIO pins of the DSC 12V tolerant? Alternatively, will plugging in a 12V signal to the power or ground pins on the GPIO damage the DSC?

The reason I ask is because we've been having issues with an apparent short to our frame, which induces sudden motion upon providing power to the robot, but the short point is unidentifiable, and we suspect the damage lies in the DSC.

The current situation is as follows: Closing the circuit breaker (giving power to the PDB) will, on occasion, incur forward motion in a number of motors that persists for a few seconds. I know for sure that the motors on PWMs 1-3 and 6-7 are moving forwards; 4 and 8-10 have no connections, and 5 may be doing so (but is unconfirmed). Later testing only saw motion in a subset of these motors (which is undetermined).

The backstory: The sensors (details later in the post) were wired with +12V and GND to a 20A PDB, a 1K pullup across the 5V and signal, and the signal wire was mistakenly plugged into both the +5V and GND (at two different points).

The one common factor that we have confirmed is that this phenomenon only occurs when the signal from our conveyor sensors is plugged into the DSC (on the signal pins). We are using Banner QS18VN6D sensors (the white signal line) for this purpose.

The camera and cRIO are isolated from the frame and we cannot identify any other potential shorting point.

We didn't get a chance tiday, but we plan to confirm tomorrow whether the point of failure is the DSC (if we can reproduce the issue) by cutting its power and unplugging the DB37. Until then, it would be great if someone could confirm our hypothesis.
Is the 5V indicator on the DSC still lit? I'm not sure you did any damage to the DSC by routing the signal line to either ground or the 5V pins. Worse case I see is if the output was at ground and you plugged it into the +5V pin in which case the on-board regulator would go into current limiting mode. Now if you had routed the 12V to the DIO or +5V pins then damage might occur. Be advised, the DIO input pin connects straight to the cRIO DIO module through the 37 pin cable.
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Unread 19-02-2012, 23:49
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Re: Potential DSC Damage

Quote:
Originally Posted by BitTwiddler View Post
Is the 5V indicator on the DSC still lit? I'm not sure you did any damage to the DSC by routing the signal line to either ground or the 5V pins. Worse case I see is if the output was at ground and you plugged it into the +5V pin in which case the on-board regulator would go into current limiting mode. Now if you had routed the 12V to the DIO or +5V pins then damage might occur. Be advised, the DIO input pin connects straight to the cRIO DIO module through the 37 pin cable.
All 3 lights on the DSC are still lit.

The 12V and GND lines of the sensors were never connected to the DSC.
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Unread 20-02-2012, 00:19
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Re: Potential DSC Damage

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Originally Posted by slijin View Post
All 3 lights on the DSC are still lit.

The 12V and GND lines of the sensors were never connected to the DSC.
As long as you were using the NPN version of the sensor (the model number you gave says it is) then I don't think you got any 12V into the DIO input so you should be OK there. You may need to look at the wiring to the sensor to see if there is a frame short there. I don't think the DSC is the source of the short but I could be wrong.
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Unread 20-02-2012, 00:31
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Re: Potential DSC Damage

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Originally Posted by BitTwiddler View Post
As long as you were using the NPN version of the sensor (the model number you gave says it is) then I don't think you got any 12V into the DIO input so you should be OK there. You may need to look at the wiring to the sensor to see if there is a frame short there. I don't think the DSC is the source of the short but I could be wrong.
The terminal block we're using for the sensor connections has been checked for a frame short, so we know the sensors themselves aren't the issue.
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Unread 20-02-2012, 00:45
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Re: Potential DSC Damage

Quote:
Originally Posted by slijin View Post
The terminal block we're using for the sensor connections has been checked for a frame short, so we know the sensors themselves aren't the issue.
Looks like you'll need to pull out the ohmmeter at it's lowest scale and probe various points to ground. Pay attention to the values you read as they should get smaller as you get electrically closer to the short.

BTW, the specs for the cRIO digital IO module (http://www.ni.com/pdf/manuals/374069e.pdf) indicate that the inputs can tolerate up to 30 Volts. (Not happily for long but it will tolerate it).
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Unread 20-02-2012, 00:57
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Re: Potential DSC Damage

Quote:
Originally Posted by BitTwiddler View Post
Looks like you'll need to pull out the ohmmeter at it's lowest scale and probe various points to ground. Pay attention to the values you read as they should get smaller as you get electrically closer to the short.
The intermittence of the problem prevents us from effectively isolating the issue, as does a lack of multimeters with that level of precision.

Thanks for your help! The 30V tolerance is good to know.
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Unread 20-02-2012, 01:34
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Re: Potential DSC Damage

Please don't do it again, it wasn't designed for this sort of situation! :-)

The short, conservative, answer is that this fault condition is not within spec, and further operation is not guaranteed. The GPIO signals are not intended for 12V operation in any configuration, the GPIO power and ground pins are intended as outputs only. Unfortunately, that isn't made clear in the documentation you linked to. I will try to include this information in the next revision.

The issue is that the GPIO pull-up resistors and ESD protection diodes provide paths for this extra voltage sneak across the rest of the board, so it could have damaged any system within the DSC. It is very likely that the board needs to be replaced, most of the circuitry is now suspect especially since an unrelated section is faulting.


The longer answer is that "a few seconds of forward motion from multiple motors" has to be the weirdest symptom I've ever heard for a DSC fault. My best guess is that it is somehow generating a single PWM pulse. Here are the problems with that theory:
1) It should generate less than a second of torque before the motor controllers shut down again. Maybe inertia makes it look like several seconds?
2) The pulse length window is pretty short. It feels unlikely that a fault could accidentally create a valid signal.

Are you using Victors or Jaguars?

Do you have control of the motors after their initial jump?

Have you tried swapping in a different DSC?


The NI9403's datasheet states that it can withstand up to +/-30V (with no impedance) on up to 8 channels. You likely applied +/-12V with 0-20 kOhms impedance to many of its channels. I can't guarantee that you did not damage this unit, but I suspect the DSC much more than the 9403.
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Re: Potential DSC Damage

Thanks for your response.

Quote:
Originally Posted by EricVanWyk View Post
The short, conservative, answer is that this fault condition is not within spec, and further operation is not guaranteed. The GPIO signals are not intended for 12V operation in any configuration, the GPIO power and ground pins are intended as outputs only. Unfortunately, that isn't made clear in the documentation you linked to. I will try to include this information in the next revision.
Good to know.

Quote:
Originally Posted by EricVanWyk View Post
The longer answer is that "a few seconds of forward motion from multiple motors" has to be the weirdest symptom I've ever heard for a DSC fault. My best guess is that it is somehow generating a single PWM pulse. Here are the problems with that theory:
1) It should generate less than a second of torque before the motor controllers shut down again. Maybe inertia makes it look like several seconds?

2) The pulse length window is pretty short. It feels unlikely that a fault could accidentally create a valid signal.
When it first surfaced*, it actually just spun around. Unfortunately, I wasn't present to observe this occurrence, so I can't provide more details than are present in the video. Later on, the issue was indeed momentary twitching upon powering the robot that would terminate after a few seconds.

*When the issue first surfaced, we had two unresolved issues. 1) There was a case short through the camera (Axis 206). This issue has since been rectified. 2) When the circuit breaker was open (no power applied), but the battery connected, we could read 12V across the +12V from the battery and the chassis. However, I'm afraid that this wasn't the issue at fault, as a)we measured 12V across the chassis, not 5V, which is the nominal spec on the camera's power line and b) the issue persisted following removal of the camera.

Quote:
Originally Posted by EricVanWyk View Post
Are you using Victors or Jaguars?
We are using 6 Victors, with 2 Jaguars on CAN.

Quote:
Originally Posted by EricVanWyk View Post
Do you have control of the motors after their initial jump?
Yes, we do.

Quote:
Originally Posted by EricVanWyk View Post
Have you tried swapping in a different DSC?
That will be the second thing we'll be doing when we go in today (the first will be, if the issue remains reproduceable, disconnecting the DSC from all sourced power).

Quote:
Originally Posted by EricVanWyk View Post
The NI9403's datasheet states that it can withstand up to +/-30V (with no impedance) on up to 8 channels. You likely applied +/-12V with 0-20 kOhms impedance to many of its channels.
The chassis short was +12V, with 7 kOhms of impedance.

Quote:
Originally Posted by EricVanWyk View Post
I can't guarantee that you did not damage this unit, but I suspect the DSC much more than the 9403.
Hopefully we'll be able to provide more details after the DSC is switched out.
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Last edited by slijin : 20-02-2012 at 23:54.
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Re: Potential DSC Damage

We've swapped out both the DSC and 9403 (given time constraints, we're not taking any risks - we'll assess failure points post-ship) and the issue seems to have desisted (although whether the issue had been persisting with the DSC in question is in itself debatable).

We've also opened the DSC in question, but there is no noticeable damage to it. Here it is:

If you'd like, we could send it to you so you could take a look at it.
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Re: Potential DSC Damage

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Originally Posted by slijin View Post
We've swapped out both the DSC and 9403 (given time constraints, we're not taking any risks - we'll assess failure points post-ship) and the issue seems to have desisted (although whether the issue had been persisting with the DSC in question is in itself debatable).

We've also opened the DSC in question, but there is no noticeable damage to it. Here it is:

If you'd like, we could send it to you so you could take a look at it.
Looking closer at the left edge of the board it appears that the resin has melted. We occurred similar issues last year and damaged 3 DSCs before locating the issue. By having the power and signal wires reversed on our pressure sensor we were sending 5V "the wrong way". In one instance the voltage was enough to desolder some of the contacts on the board. If the resin looks wavy and non uniform you have a definite wiring problem.
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Unread 20-02-2012, 23:50
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Re: Potential DSC Damage

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Originally Posted by Fe_Will View Post
Looking closer at the left edge of the board it appears that the resin has melted. We occurred similar issues last year and damaged 3 DSCs before locating the issue. By having the power and signal wires reversed on our pressure sensor we were sending 5V "the wrong way". In one instance the voltage was enough to desolder some of the contacts on the board. If the resin looks wavy and non uniform you have a definite wiring problem.
I don't recall seeing any resin damage (what you're seeing may be just the poor quality of photo resizing done by mspaint), but I didn't take that close a look at the board - making sure the robot got rewired correctly was the more pressing issue at the time I'll make sure to take another look at it tomorrow.

But three sidecars...

Thanks for your input
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