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Hi there
Although the actual system comprises of 6 STC-1000 temperature controllers I have included just 3 in the above pic to keep things simple. On the top of the diagram I got three 12 VDC STC -1000’s wired in series - if just one these controllers hits a target temperature the circuit immediately opens. K2 is a normally open contactor (12VDC coil) wired to the heating side of the STC 1000’s. K1 is a normally closed contactor(12VDC coil) wired to the cooling side of the STC -1000’s and serves as a safety – just in case the contacts on K2 ever get stuck. From K1 I got 220 VAC running to an outlet where an ozone and oxygen generator are plugged in. The sensors from all the STC- 1000’s monitor and are connected to the column reactor.
A few important points need to be mentioned here:
The content in the reactor does not heat uniformly hence the need for six temperature sensors.
Ambient temperature is always well below 39 degrees Celsius, which means the coil of K2 will be energized as soon as the system is plugged in.
Heating is the result of ozone reacting with the content inside the reactor under pressure. The reactor contains NO heating elements.
Cooling occurs naturally when ozone is no longer being introduced into the reactor. There is NO external cooling system.
When the trigger temperature of 39 degrees is hit it is of paramount importance the oxygen and ozone generator shut down immediately and permanently until a manual reset.
The main purpose of the latching relay is to prevent the ozone and oxygen generators from cycling on and off which is very damaging to the equipment as this setup sometimes is running remotely for days at a time, unattended.
An example is warranted. When all the STC- 1000’s are set at 39 degrees (heating side) and the temperature of the content inside the reactor matches this temp when a STC-1000 picks it up, current will be interrupted to the normally open relay K2 and the circuit will open. However after 20 to 30 seconds because ozone is no longer being pumped into the reactor the temperature will drop below 39 degrees and the circuit will close again. Without the latching relay the generators will be cycling on and off every 30 seconds or so, which is a big no no. Hence the importance of the latching relay.
Now if all STC 1000’s are set at 39 degrees (heating) and F2 on the STC- 1000’s is set at 1 degree (F2 sets the temperature differential for the cooling relay to kick in), and K2 fails for instance the contacts get stuck, when the temperature of the content inside the reactor hits 40 degrees, current will be sent to the coil of K1 which is normally closed and the circuit will open. However in about 30 seconds the content inside the reactor will cool down (because ozone is no longer being introduced) current will cease to K1 and the circuit will close again - just as mentioned above this begins a vicious cycle of powering the generators on and off which must be avoided at all cost.
Below is a schematic of the temperature control system:
JRW said:
"Safety circuits should always be "safe when closed / powered".
You can re-arrange things with just a couple of small parts.
Add a normal 12V relay (I'll call it the pilot relay) with the coil in place of the NC "safety" contactor coil , and use an NC contact on that relay (or two contacts in series) to control the contactor, with the contactor now also being normally open.
Put the safety contactor before the heating control contactor in the AC power contact sequence.
Feed the pilot relay coil through an auxiliary contact on the safety contactor.
Add a "power on" pushbutton to connect +12V directly to the safety contactor coil.
That should allow the safety contactor to pull in and latch when you press the start button, and if the cooling every kicks in, that will cause the pilot relay to open the coil circuit of the safety contactor - so that drops out and disconnects everything, including the power to the pilot relay, so it cannot start the system again without you pressing the power on button.
Make sure the contactor coils have flywheel diodes fitted, to avoid contact arcing that could damage the controller contacts.
If the power contactors do not have an NO aux contact, you can make the latching part with another normal 12V relay and use a contact on that to control the safety contactor."
Can somebody please help me understand (using a simple diagram) how to go about wiring the above setup? I purchased K1 and K2 from MDI, these are mercury displacement relays and have no AUX. I have understood I will need to replace K1 with a normally open equivalent and change the AC power contact sequence but that’s all. Really confused as to how I am going to set this up. I have no electronics background so that does not help at all. Hope somebody can help.
