Hi there

I am running an ozone/oxygen system (240 VAC- 7 Amps) which pumps ozone gas into a column reactor The temperatures inside the reactor are monitored by six independent sensors hooked up to to 6 individual STC-1000 temperature controllers - 120 VAC. I cannot leave the system unattended because if even just one target temperature is triggered I have to be there to manually shut down the ozone/oxygen generators to avoid an exothermic reaction. I know I can use a PLC controller coupled with thermocouple modules to automate shutdown but because this is just a research project I want to keep costs to a complete minimum. So I started researching relays and relay logic. The STC-1000 temperature controller has a relay (heating side) which is energized as long as a target temperature is not hit. I figured how hard can this be- with only one temperature trigger required to shut down my operation a simple OR circuit will do the trick- 6 SPDT relays hooked up in parallel to the temperature controllers and an additional 240 VAC 15 Amp relay hooked up to a power strip to plug in the ozone/oxygen generators. Most embarrassingly I have been at it for about a week now and I still cannot figure out how to go about wiring this safety relay. The fact that I have no electronics background or whatsoever does not help my situation at all. Hopefully someone out there can shed some light and guide me in the right direction.

 

The way I see this project is that you want the hottest location to be at temperature and all others to be slightly cooler. No spot over temperature!
Connect all 1s to the power line.
Connect all 2s to the other power line.
Connect the first 5 to power.
Connect the last 6 to the heater.
Connect all middle 6s to 5s.

The power will be on only when all the controllers want power. As soon as one reaches temperature then the power is turned off.
Is that what you want?
RonS.

 

Hi there Ronsimpson,

Thank you for your prompt reply! There are no heating elements. The ozone pumped into the reactor if not monitored will generate a tremendous amount of heat, which is something I want to avoid. So none of the STC- 1000 temperature controllers are connected to a heating element. The STC-1000’s are only being used to display temperature inside the reactor, that is all. The liquid inside the reactor does not heat uniformly with some areas getting hotter then others that is why I need 6 temperature readings.

When a target temperature is hit, the relay on the STC-1000 (heating side) will de-energize. I figured with the aid of an inverter relay the signal can be communicated into an OR circuit which would then go on to shut down the generators. Hope I am making sense. Otherwise no worries. Still very grateful for trying to help me out.

 

shut down the generators

How are they "shut down"?
Can't the relay contacts in series from the STC-1000 do that directly?

 

I figured with the aid of an inverter relay the signal can be communicated into an OR circuit which would then go on to shut down the generators.

As Ron suggested.
(Thanks Ron for the images)

 

As Ron suggested.

As sghioto suggested. The ozone/oxygen system can be powered (turned on/off) by the 15A relay. At start up, all 6 points are cold all switches are closed and the relay allows the ozone system to run. As soon as some point gets too hot the ozone machine will be un-powered until the temperature drops.

The switches in the STC1000 are 10A.

 

SRC1000 has another output for cooling so you may consider adding second relay for redundancy. it is a small addition but could prove vital if relay is stuck, also you may want to size your relays correctly (it does not hurt to pick slightly larger one, for example 15A version is plenty for 7A load).

 

Hi there Zapper

Thank you for contributing! They are shut down via a relay. The set up comprises of one ozone generator and one oxygen generator. If I understand correctly when the STC- 1000’s are wired in a series and there is a trigger, both generators will shut down regardless of which relay is used. In other words there are 6 temperature controllers labeled A,B,C,D,E, and F. If the ozone generator is relayed with temperature controller “A” while the oxygen generator is relayed with temperature controller “F” and a target temperature is hit then both generators will shut down. Is this correct?

 

Taken from post #7.
The controller normally runs a heater or a cooler.
Both your machines can be treated as a heater because they heat.
Switches A,B,C,D,E,F are wired in series. If any point is too hot the heater is turned off. (I know it is not a heater) You want all 6 controllers wired in series.
In your case you are controlling a relay that controls the ozone generator.

 

for current to pass though several contacts connected in series, each contact must be closed.
if ANY contact is open, circuit is open and current does not pass - and it does not matter which of the contacts is the open one.

for current to pass through several contacts connected in parallel, any contact need to be closed. does not matter which one.

circuit posted by ronsimpson uses contacts in series. this takes advantage of STC1000 output behavior... at low temps, heating contact is closed (need heat). so relay would be energized only when ALL of the SRC1000 are in agreement that more heat is needed.

the modified version that i posted does the same but in reverse using other contact (need cooling). this circuit is meant only for redundancy since you mentioned safety. and here the contacts from different units are wired in parallel. so if ANY of the STC1000 states that cooling is needed, K1 will be energized. to invert the state of this relay, normally closed contact is used.

finally both circuits can be combined (normally open contact from "need heat" and normally closed contact from "need cooling"). so both of them would produce same result but because of redundancy, circuit should still perform as desired even if one of the two relays fails. common mode of failure is relay contact stuck (welded on) due to overload or inductive nature of the load.

 

A wholehearted thank you to ronsimpson, sghioto, panic mode and the zapper. I do not think I would have ever figured this out. This forum has some bright minds! The redundant relay is added peace of my mind given the risk associated with this project so tip of the hat to panic mode. Hopefully I can wire everything successfully. If I have any questions I will post.

 

Something does not seem right. Please correct me if am wrong. Why would panic mode depict the circuit as normally open on the secondary (contact) side of relay K in the circuit diagram? I am referring only to the diagram depicting the unmodified circuit containing just one relay. The ozone/oxygen generators are running until a target temperature is triggered and the circuit becomes "open". Wouldn't relay K have to be normally closed in this case?

Panic mode mentioned:

“finally both circuits can be combined (normally open contact from "need heat" and normally closed contact from "need cooling").

ronsimpson mentioned:

“Both your machines can be treated as a heater because they heat.”

Is it not the other way around: normally closed contact from “need heat” and normally open contact from “need cooling”?

Am I missing something here?

 

I think the switch pictures are drawn as a switch and the (open or closed) is not true.

If I was doing this, I would put a small light bulb in as the ozone/oxygen machines. Maybe start out with one controller. Have a glass of cold water and a glass of hot water. Set the controller for room temp, so one glass is above and the other is below. Get to understand how it works. Then add a second controller and see what happens.

The theory is, if all 6 controllers are set to room temp and all have the probes in the cold water the light should be on. Move one probe to the hot water and that controller should open up and stop the light.

I have heat in the Dog house, Chicken house and Green house using this controller. And I also have controllers that turn on cooling fans, and open up the windows, if the temp is too high.

 

Wouldn't relay K have to be normally closed in this case?

Depends.
To me the diagram shows relay K in the unpowered state. Once power is applied to the STC-1000 the K relay will activate through the Heater contacts .

 

Hey there ronsimpson, will definitely heed your advice when I start wiring this circuit. However initially I need to have a basic understanding as to how the circuit works especially the modified version. Sghioto hit the nail right on the head with his response. Now it all computes!! How I would like to buy you guys a round of beer and a double round for panic mode for such a clever circuit.

 

However initially I need to have a basic understanding as to how the circuit works especially the modified version.

Dow load the manual. Read the manual. Get one working and understand it.

 

Something does not seem right.... The ozone/oxygen generators are running until a target temperature is triggered and the circuit becomes "open". Wouldn't relay K have to be normally closed in this case?

the STC-1000 temperature controller has a relay (heating side) which is energized as long as a target temperature is not hit.

and the image of the unit shows that contact (on STC-1000) as normally open.

to me that makes sense... run heater (demand heat) until temperature is reached. once it is reached, relay drops, contact opens, heater turns off and temperature will begin to decrease.

since the output of STC-1000 is driving an external relay (K), coil of K will also be energized when STC-1000 output is energized. so using normally open contact of K would be appropriate. it would work just like output of STC-1000 but be able to handle larger load.

as was already mentioned - read the manual. i did not...
i was only going by what was stated in this discussion.

this is how one unit would be wired. if load is sufficiency small, STC-1000 output could drive it directly. but in case of a failure, it is better to have external relay anyway. relays are cheaper to replace.
using NO contact of K simply replicates state of STC-1000 contact.
using NC contant of K would invert the logic... (And that too can be useful in right situation).

 

Hi there panic mode.
A clarification is warranted here. First thank you for your explanation but it was not necessary.

I mentioned: “Sghioto hit the nail right on the head with his response. Now it all computes!!”

Sghioto mentioned: “To me the diagram shows relay K in the unpowered state. Once power is applied to the STC-1000 the K relay will activate through the Heater contacts.”

After reading what Sghioto had to say, I experienced a “now it all computes” moment as I finally and completely understood how both of your circuits work - which I am very grateful to you. I may not have an electronics background but I do have common sense.

Anyway after doing some reading I realized the coils on the relays and the oxygen/ozone generators produce inductive loads which need to be addressed by introducing diodes and capacitors into your 2 relay circuit. So now I am learning about how to protect a circuit from inductive loads. If I have any questions I will post.

 

Hi there.
I am going to power the temperature controllers and the relay coils with a 12v 3 Amp DC power supply. For the 240 VAC, 8 Amp load I will use two 30 Amp relays. I will also add two switches to the circuit, A and B. Please see attached schematic. I am hoping I can dampen the inductive loads produced by the relay coils and the oxygen generator by using rectifier diodes and a RC snubber respectively to keep sparking to a complete minimum. I know where to install the diodes on the relay coils but not 100% certain if installing the snubber module on the common (C) and NC (D) is the way to go - please see attached schematic. Hopefully someone can chime in and guide me in the right direction. Otherwise no worries.

 

I know where to install the diodes on the relay coils

Not on AC coils. Only on DC coils.
I don't understand why K1 and connecting the cooling contacts.