Temperature Input for Micro 810

I have an Allen Bradley Micro 810 controller and I want to be able to wire a temperature input that will control an output (heater) so when air temperature goes too low it turns on heater when air temperature reaches high point it turns off heater. I can do the programming part I just need to figure out what kind of sensor would work and cheapest way possible to accomplish this.

I want to use 120 VAC if possible but it can also be 24 VDC.

I had one guy say that I could use a 120V household thermostat somehow but I can't quite figure out how this would work.

Any recommendations? ( I am really new to this stuff)

Paul Fisk

I want to use 120 VAC if possible but it can also be 24 VDC.

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For what purpose do you want to use 120 VAC? In a PLC, there are various voltages, one for powering the PLC itself, another for PLC input devices, and/or another for the PLC outputs. All 3 voltage levels can be the same, different, or mixed. Also there are two major types of PLC inputs and outputs: digital (on or off), and analog (continuously varying between a min and max value). The analog I/O can be Voltage or Current based. So you have to learn enough to figure out what you need. I suggest getting a free online copy of the Micro810 Programmable Controllers User Manual from the Allen Bradley web site.

Which one of the 4 models of Micro810's do you plan to use? One has 120 VAC inputs, two have 24 VDC inputs, and one has 12 VDC inputs.

That said, you will not find any analog input device that will run at 120 VAC. There are indirect methods to use an external device (such as a thermostat or temperature switch) to switch a relay contact on/off, that in turn can be used as an indirect on/off digital input to your Micro810. This is usually undesirable because the PLC does not ever know what the temperature IS (such as "75 degrees F"), only that some temperature-measuring device that is looking at the temperature thinks it is either OK or not OK (On or Off).

However, because the Micro810 has analog input terminals for 0-10 VDC analog devices, you should use a temperature transmitter and sensor (thermocouple, RTD) that puts out a proportional temperature signal with a range of 0 to 10 volts. This will allow you to read a temperature directly into the Micro810.