What to use for a cabinet fan alarm?

A

Thread Starter

Augustine

In many of the indoor cabinets that I have used, we usually put a thermostat (a standard Rittal accessory) on the cabinet to give an alarm contact if the temperature goes up.

Recently some projects are asking to install a fan alarm instead, which is meant to give a pre-alarm in case either of the cabinet exhaust fans stop, which may lead to cabinet temperature rise.

I have tried a few sensing methods; using a micro air flow switch near the vent (gives a false alarm as alignment of the flow sensor against the air flow is difficult to adjust), using a current transformer and sensing relay (quite expensive), DC fans with built in alarm contact (not common and long delivery time)

Anyone has used an effective and low cost method?
Appreciate if you can share your experiences.
 
B

Bob Peterson

There are fans that have a built in sensor that gives a pulse train output that can be monitored to determine the fan speed. The fans with these sensors are not real pricey but what they connect to is not usually real cheap. And all it proves is that the fan is rotating. Not that there is any air movement.

i have yet to find anything effective and low cost. Plenty of effective means, but none are low cost.

--
Bob
http://ilbob.blogspot.com/
 
C

Curt Wuollet

Take a close on rise thermal disk switch, attach a 1watt metal film resistor across the power supply. Mount in airstream. As long as the air moves the switch stays cool. If it stops the switch gets heated and opens. Values depend on the ambient temp. Cheap and effective.

Regards
cww
 
S
I'd suggest either a photo that looks through the blades (conveyors detect jams this way with a prox looking for periodic changes of state), or a roll-your-own version of the current sensor. Shunt resistor + comparator + optoisolator = current alarm that you can input to the PLC or wherever the alarm goes.
 
Top