While the subject of blowers is being talked about, I would just add
that Herga in the UK:
Herga Electric Limited
Northern Way
Bury St. Edmunds
Suffolk IP32 6NN
UK
Telephone: +44 (0)1284 701422
Facsimile: +44 (0)1284 753112
have a couple of quite nice switches that are ideal for detecting fan
failure. Their model 6753-00 and 6553-OF both seem suitable. RS and
Farnell both sell them in the UK, but I managed to get a free sample
directly from them. The switching point is adjustable from 1" of water
to 10" of water, and is set to 2" of water on leaving the factory. There
are both NO and NC contacts, which can switch 500mA at 250 V, although
its reduced at low pressures, in a way they have not measured.
I configured mine as a differential, measuring the difference between
anode and cathode compartment pressures. This should detect a blocked
outlet, which measuring the cathode compartment pressure relative to
atmospheric will not.
G8WRB
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