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cFP-RLY-425 Error: Over temperature sensor has tripped


We have a strange problem with a cFP-2000 / cFP-BP-8 / cFP-RLY-425.

In MAX, we sometimesget this message in the 'Status' column : ( It is intermittent and may takes day to occur)

Over temperature sensor has tripped

This freezes the system since we can no longer operate the relays after this error occurs.

When the error occurs, only 3 of the 4 cFP-RLY-425 are in error.

All channels are in error.

There is another cFP-RLY-425 and a cFP-RLY-421 that works well.

When we power off and on cFP-2000, the error disappears.

We need some help and we cannot find any documentation regarding this error.


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Message 1 of 8
Hello mstlaurent,

There are a couple of things that can cause the over temperature sensor to trip. 

The first is flyback current from your load.  If you install flyback diodes across your load as described on page 9 of the cFP-RLY-425 Operating Instructions that should limit the flyback current and may eliminate this issue.

Another thing that can cause over temperature errors is switching the relays too quickly.  If you slow the relays down, do you still see this issue?
Ching P.
DAQ and Academic Hardware R&D
National Instruments
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The LabVIEW program was not running when the problem occured and all relays were opened.

The relays operate some small solenoids valves. We will try to add some protection to eliminate this cause.

Why the over temperature protection would trip on all channels of three modules at the same time?

Is there one sensor per module or one per channel?

Is there a way to read the temperature sensor?

If the temperature was really too high, why powering the controller off and on cleared the error?

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Message 3 of 8
Hi mstlaurent,

There will only be one over temperature sensor for the entire module, that is why you are receiving the error on all channels.

There is no way to read the temperature sensor yourself.

Once the over temperature sensor has tripped, it will continue to report the error until the module is reset.  It could be that the temperature sensor is just outside of the trip range and comes back to within the appropriate limits in the time it takes to reboot the controller.  The other possibility is that the sensor is tripped and has cooled to within specifications before you restart the module.

Please let me know if you have any further questions.
Ching P.
DAQ and Academic Hardware R&D
National Instruments
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Message 4 of 8
Is there any way to monitor this sensor to know when it trips?
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Message 5 of 8
Hi pti,

You can monitor the error out of the FP Write you are using to write to the relay module.  If you get error 33497, you will know that the over temperature sensor has tripped.  See the image below for more information.

Please let me know if you have any other questions.

Message Edited by Ching P. on 10-24-2007 11:03 AM

Ching P.
DAQ and Academic Hardware R&D
National Instruments
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Message 6 of 8

We are using the cFP-RLY-425 to provide 24 VAC to a relay (we also have another system which use 120 VAC relay).

Speed cannot be a problem since the relays are switched only when the user operates a control on the user interface.  Moreover, the problem occurs even when the system is idle.

We tried to add a MOV on each channel but the problem still happens. This is what we installed:S07K130, Max. voltage: 130 VAC, 170 VDC, 9.5J, response time < 25ns, Varistor voltage@1mA: 205V, Max clamping voltage: 340V - 10A.

It seems like we experience the same problem than this other customer:

We have used many cFP-RLY-421 in the past without any problems. It is the first time we use the 425. We use them on two different systems and we have the same problem on the two systems.
On one system, we have two 421 and two 425 and only the 425 are giving us some problems.

Do you have any other suggestions for troubleshooting?


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Message 7 of 8


Ching's reply implies that the internal overvoltage protection may be causing the extra heat.   Docs for the 425 state that this internal protection will cause some leakage current.  You might run an experiment where you disconnect all external wiring to 425 module and see if it still trips on overtemp.  If it stops tripping out, then a much harder look at internal protection is warranted.

You mentioned that one of the 425's did not trip out.  Anything different about number/type of loads connected to that module?  Have you tried swapping the actual 425 modules around to see if problem moves with module or stays with position on backplane?

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Message 8 of 8