Abrysiuk (Customer) asked a question.
I am trying to figure out a cheap hardware solution to getting room temperature readings into my PLC.
I have a Click PLC (Ethernet) currently running my 5 zone in floor heat system. Currently, it runs digital inputs only, being mercury thermostats. I have this system integrated into Home Assistant via Modbus.
I'd like to switch it to reading the room temperature directly by the PLC, with set points in-memory (modified by Home Assistant over modbus).
The software side seems simple enough, but I'm a little overwhelmed by the hardware options. I am trying to use the existing 2 conductor cable runs to the existing thermostats.
Is my research right in suggesting a sensor and transmitter for each that would output 4-20ma into an analog module (or 2) for the PLC be best? Do I understand right that the transmitter would be powered and read from the same two wire loop?
I'm thinking RTD, as that seems to be the most accessible. Something like the new RTD1-01-02 wall sensor with a cheap -50 to 50 C pt100 transmitter. Assuming from size, though tough to tell, that the transmitter would fit in or behind the enclosure for the wall mount sensor. Is this advisable? Or is there a cheaper way (per unit) to do it, while keeping the logic internal to the PLC? (avoiding relying on HA to relay temperature sensor info)
I use a small bit of thermocouple wire attached to a temperature transmitter that sends a 4-20ma analog signal to my PLC. the 4-20ma is far more stable than long thermocouple wire or even 0-10v analog signal so temperature reading is better when doing long runs on 4-20ma. Be sure and use a smoothing filter over the signal to make it fully stable. For home environment doing basic room sensing you can probably use something like 5-10 seconds and be plenty fine as thermostats often use 5+ second filters.
These are the transmitters I use:
https://www.automationdirect.com/adc/shopping/catalog/process_control_-a-_measurement/temperature_sensors_-a-_transmitters/temperature_transmitters/xth-0100f-j
And they are just taking 2 wires in to power them and send the 4-20ma signal, and then the short thermocouple attached to other terminals. I am using some shielded RS-485 wire for my setup, but your existing wire will probably work fine as it supports the voltage
I've used these on control panel doors at some RTU location where the customer wanted temp and humidity and they were pretty handy.
https://dwyer-inst.com/en/rhp-3n44.html
They are loop powered and I think you can get it with only temperature.
My answer is a question. Is there a yaml for Home Assistant to connect to a Click PLC via Modbus?