Ok, I know there has to be a simpler way of accomplishing what I want to accomplish, but I can't really see it right now. I have 4 5HP 3PH 208V exhaust fans, each controlled by a VFD, I want all exhaust fans to turn on when the temperature exceeds 90 degrees Fahrenheit, and turn off when the temperature drops below 90 degrees Fahrenheit. Between 90 and 125 degrees I want all 4 motors to ramp up to 25% or around 525 rpm, between 120 - 130 degrees to 50% or 1050 RPM, from 130 - 140 degrees to 75% or 1575 RPM, from 140 - 150 degrees to 100% or 2100 RPM, and 160+ degrees, I want the motor to ramp up to 125% or 2625 RPM. I also have a CO Monitor with 24V control relays that I want to turn the fans on to 25% when 22 ppm is reached, and then to 100% if 28+ ppm is reached.
My only thoughts would be to use small PLC controller to control all 4 VFDs, and then have a digital temperature probe as an input and the CO monitor as two on/off inputs for warning and danger conditions. I realize that a setup like this would be quite expensive, so I am trying to think if there is anything less that would do the same thing, or if this would be my best bet.
