Engineers thermometer

I have just configured an emonGLCD and a battery-powered emonTx unit with 3 temperature sensors. This would make a useful heat-pump engineers tool, and probably has many other uses.


The emonTx has 2 probes (DS18B20's) on 2m cables, and one on-board the PCB. It's battery powered so can be put anywhere in range. The emonGLCD display shows the 3 emonTx temperatures and also a local temperature.  Temperatures are transmitted via wireless from the emonTx to the emonGLCD every 2 seconds.

Typical uses would be for balancing radiators. i.e T1 on the flow, T2 on the return. I have added T1 - T2 (delta T) because that is what you are often looking for.   It could also be used for air-in, air-off off an air source heat pump, or and flow/return situation.   It would make a good tell-tale device. i.e. to alert if any system goes out of its best operating ranges.

I also have the temperatures data going to a Nanode emonBase to be logged to emoncms so that graphs can display temperatures over time. You really need this to balance up central heating radiators. i.e. fix it to a different radiator every day and compare results. The flows can be balanced accordingly.

The DS18B20's are not ideal because they are a bit chunky (as opposed to thermocouples). On the other hand, the accuracy is excellent and it seems that the values can be relied upon. I have chosen to pot-up the probes myself.


They are fragile, and the ready-made sensors from the OpenEnergyMonitor shop are much more rugged and can easily be tie-wrapped to a copper pipe and insulated etc.

Next thing is to battery-power the emonGLCD so it becomes a portable tool.  

Another addition would be a LCD pulse input. This would give me a reading of kWh, and would save me using a stop-watch, as I have many over the years.

Adapting these devices could get addictive!!

By John Cantor heatpumps.co.uk

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