Wireless monitoring of temperature and humidity in a smokery

Hi everyone,

One of the projects I am involved in is a smokery producing cured and smoked fish and meat.

We have a cure chamber (used to produce salamis, cured hams etc), cold smoker (used to produce cold smoked salmon) and chiller (used for air drying bacon) and for each of these three spaces I would ideally like to be able to:

  1. Monitor the temperature and relative humidity remotely
  2. Log data locally as a backup
  3. Set notifications that trigger if either T or H stray out of a defined band

I’ve looked at the getting started guide and my interpretation is that the emonBASE and three emonTH will do the first two but it looks like that notifications and alarms on emoncms might be in the works but not yet available?

I’m also interested in monitoring the building’s electricity consumption. The building has a single phase supply feeding into a dumb meter.

Am I right in thinking that for this I would need to add an emonTx and CT sensor and then that would communicate with the emonBASE?

Again I would like to be able to trigger a notification if the building’s power drops out. I suppose in that scenario emoncms stops receiving data but is there any functionality that triggers alarms or notification in that eventuality?

This combination sounds like the most cost-effective option. Is there any reason why I should go for the emonPI over the combination of emonBASE and emonTX?

Final question: my understanding of linux is zero. How much do I need to learn in order to be able to make this setup work?

Thanks in advance!


I can answer the electrical and hardware part - you’ll need someone else to advise the details of alarms etc, but I believe it’s possible.

Not starting with the first question:

  1. An emonPi is (in effect) an emonBase with a 2-channel emonTx built into the one box. So if you can locate an emonPi close to your meter, and there it will also receive the radio transmissions from the emonTH’s, then it’s equivalent to an emonTx and emonBase. But one possibly important difference for the future: the emonTx offers the ability to monitor 4 channels of electrical power. You need as many CT’s as powers that you want to monitor. I’m guessing the principal load is the chiller, but if there are others, you might want the total building on one channel and the chiller on its own on the second.

  2. Both emonBase and emonPi can run the same software, which will log the data and present it as a web page.

  3. To read true (real) power, you also need to monitor the voltage. Otherwise, you get a guessed value of apparent power assuming that the voltage is always the nominal value. For the chiller motor, real and apparent power could be very different. The speed of rotation of the disc in your supplier’s meter is a measure of real power, and that’s most likely what you’re charged for.

  4. The three emonTHs will do what you ask - but first check that they will operate over the temperature and humidity range that you have.

… the emon[Pi | Base] will stop working unless you run it from a maintained battery. If you need remote indication, everything involved in that must also be battery-backed, of course.

I wouldn’t let that put you off. We’re trying hard to make everything not require an understanding of Linux, and provided everything goes right, you shouldn’t need it. If you can navigate round the file system and list directories using a terminal and DOS-like commands, and copy instructions, that’s probably about all you’ll need. Obviously the more you get to know, the less you’ll need to look up.

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@cagabi has been working on a emoncms module called the task module GitHub - carboncoop/task: An emonCMS module that implements notifications. Its not a standard part of emoncms yet and will likely require linux commands to get going, Carlos may see this and be able to help.

An alternative could be to use NodeRED: Node-RED - Guide | OpenEnergyMonitor

Yes the chiller is likely to be our main load as it’s cooling our cold room down to about 5C. It’s on a dedicated circuit so there is scope for measuring it. The cure chamber is probably a similar volume, likely worse insulated but will only be cooled to about 12C using an AC unit (which is spoofed into operating below 16C by a CoolBot). The AC unit is not on a dedicated circuit. So realistically I can’t see us needing four channels of power monitoring but 2 might be nice. But looking at the prices in the shop I think the emonBASE plus emonTX is cheaper than the emonPi isn’t it? Is there a benefit to us opting for an emonPi?


Although it’s an industrial building (Victorian mews still used for light industry) the meter says it’s measuring kWh which implies apparent power. Still, would be nice to have both though.

Good point! I see they go up to 80% RH. Our typical target is about 70% to 80% but some cured meats need 80% to 90% for a time. I see this sensor goes up to 100%: https://openenergymonitor.com/sale-dht22-temperature-humidity-sensor-am2302. Is there a low cost and straightforward way of incorporating this more capable sensor into this setup?

Yes good point. I’ve seen simple 3 pin plugs with capacitor and GSM connection which would probably suffice for our needs.

Grand, I’m sure I can manage that.

OK this sounds beyond my capabilities for now but it sounds like something that’ll be doable at a later date.

Thanks very much for the considered responses both of you! I need to do some more digging in the documentation and shop to try and work out how it’ll work and how much it’ll cost. I’ll be back…

I hadn’t compared the shop prices. The emonPi comes with a 2-line LCD display in an aluminium case, the RPi case is plastic.
I think you’re right, the emonBase does come out cheaper.
I think your list is:
RPi + case + RFM69Pi + SD Card + USB power supply & lead
emonTx + a.c. adapter + 2 x c.t.

You’ll need a power socket reasonably close to the emonTx to measure the mains voltage and provide it with power.

No it doesn’t. kWh is (real) energy, real power is kW, apparent power would be kVA.

I pass on that, I think @glyn.hudson will be able to tell you.

The Si7027 temp/humidity sesnor used on the emonTH V2 (current version) is much ore capable and efficient tha the DHT22, see sensor specs comparison table: emonth2/sensor at master · openenergymonitor/emonth2 · GitHub

The version of the si7021 that we use on the emonTH V2 (SI7021-A20-GM1R) is fitted with a hydrophobic and oleophobic membraine which should improve perforamce in high humidity and dusty / smokey enviroments. Altuough it’s expected that % accuracy will drop at close to 100% humidity, see Si7027 datasheet: