WildWest

Hi All, Okay, I finally got around to measuring the trip points as requested. As best as I can tell, the circiut tripped at approx. 50K ohms and reset at around 1k. I still want to build an indicator that mimics the air flow switch, so any ideas will help. I would like for it to be able to run off battery power if possible. Thanks Again, Robert

I actually thought about replacing the switch but it is not a standard micro switch. The actuator is a custom piece as well as the enclosure so attempting to change the switch might be more difficult than it appears. Couldn't really measure the current to the switch but I expect it is low. The switch wires are 22 ga. so not alot of current. As for the threshold voltage on the logic board, all I can tell is that it is at +25vac or GND. I still have not been able to locate a good set of schematics for the controls on this machine so I am just going by what I can measure. Thanks, Robert

Thanks for the response. In further checking the switch is not actually in series with the gas valve, it is an input to the control logic PCB. As a facility / enginnering plant engineer, I am well aware of your safety concerns. This switch is monitoring the air flow to the unit (commercial dryer) and when the air filter is getting dirty. The unit will still run but there is no indicator to the operator that the heat has been shut off. I am trying to install a small led to tell the operator that the filter needs cleaning (under normal conditions the filter is cleaned 2-3 times a shift). So, something simple that will not effect the normal operation of the unit is what I am looking for. Thanks again, Robert

Hi All, I need a simple circuit that will light an LED when contacts of a micro switch open. The switch is in series with a gas valve which operates on 24vac. In the "normal" operating state, the switch is closed and the gas valve is allowed to operate. When air flow is low, the switch opens taking power away from the gas valve which will then shut off. The switch only has two connections and it has to be as simple as possible. I want the LED to come on when the switch opens to let operators know the heat is off. Any ideas on a simple circuit would be apprecated! Thanks in advance, Robert