Recycling a phytotron

A research center gave me two stunted phytotrons, which went to the dump.

After a few hours of technical analysis, the automaton and the hose of the peristatic pump were broken.

I dismounted the phytotron, to identify its function, to look where the sensors were.

The phytotron consists of a neon light arranged vertically on three sides. We can turn indepandement three groups of neon, to adjust the intensity of lighting.

To manage the temperature, the phytotron consists of a cold group and a heating resistor.

The cold unit consists of an evaporator positioned in a sealed chamber isolated from the outside and a capacitor.
To activate the cooling unit, simply actuate a solenoid valve.
Once activated the temperature goes down but also the humidity, important way.

To manage humidity, an Ultrasonic Humidifier from Contronics, model HU-25 is installed.
It consists of a peristaltic pump that fills the tank automatically, thanks to a float. It automatically changes the water in the tank every hour with a solenoid valve.
The humidifier can be operated by a dry contact.

the sensors. The sensors are located in the hermetic chamber next to the evoporators. There are three PT100 probes and a humidity sensor.
Two PT100 probes to manage the high and low safety cut. And a probe to measure the temperature of the phytotron.

I wondered why put the sensors in this place? Was there not a problem in the measurement of the parameters.

To be clear, I replaced the PLC with ours, you can see below, a PLC based on a Raspberry with a GSM and a fieldbus. I changed their relay card by our card. And placed our multifunction sensor (T °, H °, CO2, TVOC, Patm, LUX) in the culture chamber.

I wrote a little program and I launched the phytotron. Parameters: 20 ° C and 60% humidity.
Measuring at different points of the phytotron from bottom to top, the temperatures were very different from 27 ° C to 24 ° C.
It was therefore necessary to make an important software correction. In addition to the latency of the sensors and the renewal of the air by the wind, the system was complicated to manage.
So I placed my sensor in the middle of the phytotron. And the results were superior.

My little program manages the temperature well, for a temperature set at 20 ° C with a hysteris of 2 ° C is a control every 30 seconds, the temperature varies between 20 ° C and 22 ° C.
For humidity, it gets complicated.
I tried several things, turn on the humidifier at the same time as the cold group, to counterbalance the induced decline. Then do a moisture analysis every two minutes with an activation of 5 seconds. But the results are not terrible.
For a humidity set at 60%, I have a variation between 50% and 70%.

If there is someone who wants to modify my program, it is with pleasure.

The next steps :

  • change neon lights with leds
  • add an irrigation system

And why not organize a contest with the two growth chambers, I could enter two teams in the control of growth chambers, and see which are better grow plants.

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