> Rather than having to add on an airflow sensor of some ilk, > there are two other options that might be easier: > > 1. Use fans that have a fail indication lead. Most fans, > specially the PC variety, have a third wire that is used as > a tachometer. Most give two squarewave pulses per rotation.
Might not help if the blower cage or fan blade assembly falls off or becomes disabled along with the air flow (path) failing to reach the target. Unless the motor monitor circuit is smart enough to catch overspeed or high/low current the motor will keep going while the circuit heats up. > 2. Rather than relying on detection of the fan rotation/airflow, > why not use a thermostat instead (Klixon variety). That way you > know if your PA is actually in the danger zone due to either a > fan failure or site HVAC failure or other condition that causes > the temperature to go above the limit. If the blower is used to cool a tube pa the thermostat detection hardware is probably way to slow. By the time the temp has triggered the thermostat the tube and/or adjacent circuitry might have already gone way past a reasonable high or max temp. Might be alright if the pa is solid state even though I'd try to keep the thermal cycle values under control with an earlier start blower system. Many vane indicators are of the long arm micro switch type. Easy enough to make your own but you can probably find them through companies like McMaster, C&H Sales Company, Grainger (all in Southern California) and many Heating & Air Conditioning Supply Stores. A number of possible microswitches can easily be adapted to airflow vane switch applications. C&H Sales sells or sold a lot of long arm units and numbers like the MICRO YZ-2RL come to mind as a possible option. If you want to get creative with a valid switch interlock the Cheery E20 110P1157-D is a cute switch to think about. cheers, s. > > I'm looking for information from anyone who has experience and > > could recommend a good vane switch to be installed on several > > repeaters. Some of my machines are 2 1/2 hours from my house > > so visiting them often just doesn't happen. > > > > I would like to install a vane switch to monitor the PA Fan and > > connect the output of the switch into the sites SCADA system. > > > > Manufacturer, model #, price, and opinion would be greatly > > appreciated.
