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'Fail safe' for U6/RB12?


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#1 particleman

particleman
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Posted 06 April 2015 - 09:43 AM

Hi there,

We recently had the bad luck to have a laptop linked to a U6 stolen from a research site. The U6 is controlling several 110V heaters (T measured via K-type thermocouples) via solid state relay modules on the RB12 board and PID control in DAQFactory, and a few of these heaters remained turned on when the computer was stolen. Fortunately, things are well insulated and components are safe for high temperatures, so nothing went up in smoke, but I would definitely like to avoid this possibility in the future. While I do plan to not have computers stolen in the future, I can see a connection being accidentally disconnected or something similar... 

 

Any suggestions about how to make this fail safe (i.e. for the relays to return to open/default when the LJ is disconnected)? One option is to have a thermostatic switch that cuts heater power if things are getting hotter than they're supposed to, but if would be great if there was a simpler way.

 

Any suggestions would be appreciated....

Thanks.



#2 LabJack Support

LabJack Support
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Posted 07 April 2015 - 07:45 AM

The RB12 has pull-ups on each input signal that hold them high if no LabJack is connected, which should put each module in its disabled (normal) condition.  If your modules are normally-open, you should be good.  Try testing with just the RB12 (disconnect U6 from RB12) and with the RB12 & U6 (disconnect U6 from host).

 

I assume the U6 is powered by the host through the USB cable?  Does the RB12 take power from the U6 or do you have a power supply connected to the RB12?

 

One other thing you might consider is using the Watchdog to reset the U6 in the event that the host stops talking to it, and at reset have all lines go to input:

 

http://labjack.com/s...rs-guide/4.3.13




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