I have an M1 temp sensor mounted in my weather station to monitor the heater under the rain collector to avoid freeze up and damage to the collector(it is in a weather protected area). My wire run is about 150 ft from the ELK. The first 100ft is Cat5e and runs from the M1G to the opposite end of the house. The outdoor run uses 5 wire sprinkler system wire and it is buried underground out to the weather station. Two of the outdoor wires in the 5 wire cable also carry 24vac @1amp to supply the heater power. The other three wires in the sprinkler wire cable connect to the +12, Gnd., and signal wires from the Cat5e cable for the temp sensor. I have not been able to get an M1 temp sensor to operate reliably across this connection. As an alternative, I built up an LM34 circuit and scaled it up 10x to 0-10v using an op amp and while it operates correctly on the 100ft Cat5e run, the output voltage reads over 11v(should be 3.4v at 34 degrees) when installed in the weather station. I have rung out all 5 wires in the outdoor cable and all check out(no open conductors, and no resistance measurements between wires). I am currently thinking that the 1amp/24vac signal may be coupling over to the low power wires for the temp sensors. Does anyone have any other ideas of what might be going on?
Temp Sensor Wiring Issue
- Thread starter foxtail22
- Start date
The ELK M1ZTS should work just fine at 150 feet. Are your results better with the 1amp/24vac disconnected at the source?
You may be seeing two effects. One is the coupling of the 24VAC into the signal wires. Disconnecting the 24VAC source as suggested is a good test for that.
Not knowing the signals from the M1 sensor, the other thing that comes to mind is the voltage drop for 150 ft of cable. The power supply current travels in the ground wire so the voltage representing temperature at the end is higher than at the sender. If you had a spare wire you could use that as a signal ground but you don't. If you used the 24VAC (with appropriate power supply circuitry) to power the LM34 (or possibly the M1 sensor) you would have the extra wire needed. You could also use differential analog signals to cancel the noise pickup.
You could put a small micro at the station and send the information serially but that's getting a bit complicated...
If all you are controlling with the temp sensor is the heater just put the controller at the station with the sensor and heater and avoid sending the signals over the long cable.
Not knowing the signals from the M1 sensor, the other thing that comes to mind is the voltage drop for 150 ft of cable. The power supply current travels in the ground wire so the voltage representing temperature at the end is higher than at the sender. If you had a spare wire you could use that as a signal ground but you don't. If you used the 24VAC (with appropriate power supply circuitry) to power the LM34 (or possibly the M1 sensor) you would have the extra wire needed. You could also use differential analog signals to cancel the noise pickup.
You could put a small micro at the station and send the information serially but that's getting a bit complicated...
If all you are controlling with the temp sensor is the heater just put the controller at the station with the sensor and heater and avoid sending the signals over the long cable.
I found the issue. The signal wire was intermittent and clearly has a break somewhere maybe caused by the frost we have. In any case, I tested it recently and it was fine but today, I caught it going in and out. Since I did not have spares, I decided to use one side of the 24vac loop as a common and that along with the other two good wires gave me the three connections I need for the temp sensor. The 11v I was seeing was actually the ELK pull up on the zone input because the circuit was open. Thanks for the suggestions.
BraveSirRobbin
Moderator
Also, watch the power supply to the op amp itself, as that op amp may be providing noise, though it's odd you stated that the cat5e run works with it in place.
After finding the intermittent wire(works/fails with outdoor temp swings), I decided to try sharing one side of the non-grounded 24vac loop as a common to get by unit warm weather when the ground is not frozen and I can run a new cable out to my weatherstation. Not wanting to risk frying one of my $80 Elk temp sensors, I installed my $10 LM34/OpAmp circuit and it has been working fine. I set up rules to test the 0-10v analog levels and send range messages(for ex: temp is 40-50 deg) to my keypads. I also found that I can use the voice fields in non-alarm zones being used for other automation tasks, to speak the ranges over the ELK speaker. This handy to know as it provides the ability to speak and message for things that would not normally provide voice support. I trigger the temp report with a function key on a keypad.
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