Thermocouple Temperature Controller

[Reloadron]

So here is a description of the entire system just to help clarify. In the images of the whole system, the very, very fine thermocouple wires extend out of the center of the heating pad. There are also a set of black/red and black/yellow wires that run from the edges of the plates out of the box and into the dimmers (to be honest, I'm not sure what the dimmers are for). From my understanding, the thermocouple is not what is controlling the temperatures, but rather what is measuring it. Is that correct?
That would leave me to believe that the larger wires connected to the dimmer would control the power being supplied to the plates.

Also, if someone could explain what the function of the controller and the relay are in general that would be helpful. I literally do not know much of anything about electronics so if you could spell it out in laymen's terms as best as possible that would be helpful. Abbreviations and acronyms are hard for me to understand aside from AC and DC. We actually do have a DC power converter that plugs directly into the wall socket which makes me wonder if we even need the relay module at all. To me it sounds like the relay is just to drop the voltage from anywhere up to 250 volts back down to twelve. Is there a way I can just plug the DC power supply directly into the controller without the need for the relay?

The DC power converter wall plug has two wires, one brown and one white, but I'm not sure which wire is positive and which is negative.

If I do still need the relay module, then I can still use the diagram showing the thermocouple leads going into the controller. That part makes sense to me. What kind of wire runs from the open collector outputs to the relay though? I don't think I have those wires.

The temperature range that we are trying to achieve is anywhere from 0 to 40 degrees celsius. Are these temperatures too low for the PID controller.

My take on what you have is this. The large wires on the heating pads are power to the pads. Yes, they run directly to the dimmers. The thermocouples actually just measure temperature. The thermocouple itself does not "control" anything, it merely provides a signal proportional to the temperature in the heating pad center. I believe they were to allow you to monitor temperature. Enter the dimmers. The dimmers were used to provide an adjustable voltage to the heater pads. The lower the voltage to the pad, the less current the pad will draw and the less heat it will produce. Therefore, if you only read the temperature using the thermocouple, you could adjust the dimmers to hopefully maintain the desired temperature at the heating pads. This involves sort of finding a "sweet spot" on the dimmer. This is really not control. The Omega controller you have could be used to simply monitor the temperature of the pads. Then the dimmers slowly increased and allowed to settle searching for the sweet spot. This amounts to placing a pan of water on a gas stove and slowly increasing the flame to maintain the water at a specific temperature. As long as room temperature doesn't change and not too much water evaporates (the water is the load) we can hope to maintain the temperature fairly well.

The drawing I provided actually uses the Omega controller to control the temperature based on the temperature received from the thermocouple. This is where the method used with the controller for control can get a little complicated. The simplest method is what they call On / Off control. The controller has a set point, that being your desired temperature. When the process variable (the temperature of the pad) is below your set point the controller closes a relay and applies voltage to the pad. When the process variable meets or exceeds the set point, power is removed. The On / Off cycle repeats. The load (your petri dish) will hover above and below set point. There are many factors that will determine how high and how low (deviations from set point) you will have.

Your controller also offers what is called PID (Proportional Integral Derivative) control. This is a complex process but in real simple terms the controller looks at the process variable and the set point. As the difference between PV and SP closes the controller will for one example begin to pulse the relay providing power to the heater. This prevents a large overshoot in temperature and the process should maintain a much better control maintaining SP (Set Point).

Now you mention a temperature range of 0 to 40C (32 to 104F) if you have heater pads and no way to make cold then there is a problem as you can never get a temperature below ambient room temperature.

Back to the heating pads. I have assumed they were simply heating pads. Another member made a good point. There are devices called peltier pads that can make hot and cold. I have based everything on heating elements or heating pads.

Ron

 

[curoi]

Thanks!

So I definitely understand the components of the system well enough now. My only concern is now wiring the setup. It was mentioned that we should test one heating pad component first; that's what I've been doing. As far as connecting the controller to the relay, is there a special wire I need to have to connect the two? Also, the heating supply wires in the diagram do not give any indication as to what is positive and negative. The wiring of the output seems to just run into another wire (i.e. I don't know how to the the schematic). As far as the schematic goes, everything looks good then right?

 

[Reloadron]

If the heaters just have the two large wires extending for power and they are not labeled it matters not as to any polarity. You can just connect and run a single pad which is a good idea. If you look at my drawing the pads, relays and everything is just redundant. I believe I showed the devices with pin numbers so just setup for example channel 1 and omit the rest. I tried to draw it out for basic point to point wires. That was one reason it was so large.

I would suggest you read the controller manual to set it up. I would also try On / Off control initially and observe.

Ron

 

[curoi]

power supply

As far as the power supply goes, I can just wire that to the relay? The power supply is a 12V DC converter that plugs directly into the wall. I'm just trying to figure out how the power supply plays into the whole system (how it relates to the relay and the controller).

Also, what kind of wires do I need to connect the controller to the relay?

 

[KeepItSimpleStupid]

What is the rating of your 12 V power supply? Either the AC rating, DC rating or the power rating will do? Might say things like 240 VAC 0.1A, 24 W, 12 VDC @ 2 A etc.

The wires to the controller can be just about anything. You could use stranded Ethernet cables which would have 8 wires, or you could use 24 AWG single pair cables. Stranded wire is best. Labeled pairs help in troubleshooting. These would be the wires from the Open collector outputs to the controller input.

The wires to your heaters would be 16 to 18 AWG.

The "12 V DC power supply" supplies the voltage to the heating elements. We are assuming it's a low voltage heater.

The controller has limited power available, so a small amount of power is used to "turn" on a larger relay.

The larger relay, acts as a switch and cycles (or varies the on and off time) of the 12 VDC to the heater. IF the dimmer is used, then a lower voltage is applied to the heater. Polarity must be observed for the dimmer input, but not the heater.

I'd suggest you do the following. Go to an autoparts store and pickup something like an 1157 lamp and socket. Attach the thermocouple to the top of the lamp or drape it there. You can use the controller to control the lamp temperature. It's a great way to actually see for yourself what's happening. Connect the lamp where your "heater" would go.

When I was testing temperature controllers that controlled mains power, I used a 500 W lamp.

 

[curoi]

Relay Outputs

On the circuit diagram, how do the inputs and outputs work? The diagram for this part is confusing. The COMM RY Pins 2, 5, 8, 11 all connect to each other and then to the "12V Heater Power" (The negative or positive end?). There is no mention of positive and negative on the outputs at all. It looks like I connect one end of the power supply (12 V Heater Power Common) to the heaters but I'm not sure whether or not it connects to the positive or negative end of the dimmers. Pins 3, 6, 9, and 12 are labeled as being connected to the heater directly and are labeled with a 1. Coming out of the heater element it's labeled 2. (is that what is positive and negative?)

 

[KeepItSimpleStupid]

I'll discuss the outputs because I'll have to do some reading for the connection from the controller to the relay module.

Lets say your heaters are labeled 1A, 2A, 1B, 2B etc where A to whatever is the chamber number.

It's customary to use the negative for common unless there are other reasons to do so. Think of the (2) terminals of the relay module as a switch.

I think a good way of connecting things is to keep the dimmers powered all of the time and switch the positive. The dimmer has a V+(in) and a V-(in).
So all of the V+(in)'s get connected together and terminate at the V+ of the 12 V power supply and all of the V-(in's) get connected together and terminate at the V(-) of the power supply.

Now you can think of the dimmer as the power supplies.

So, each V-(out) of the dimmer gets connected to one terminal of the heater. Pick a convention and go with it like make pin #1 of the heater negative.

The V+(out) of the dimmer would connect via the relay module (which acts as a switch) to the other terminal of the heater.

So, if you wanted to try temperature control without a controller, you can place a JUMPER across the corresponding terminals of the relay module. A jumper is just a short piece of wire connecting the terminals together while keeping the original connections.

The power supply has a polarity.
The dimmer has a polarity.
The heaters will have a convention, meaning whatever you decide depending on how it's labeled.

Some examples are 1+, 1-, 2+, 2- or a1, a2, b1, b2, or 1, 2, 3, 4 where say odd numbers are negative.

Aside: When you have to wire large systems, it just makes sense to refer to the wires and cables and then have a sheet which defines the ends. It also makes sense to have a cross-connect area. An example is telephone in a building. Rooms are wired to specific terminal in a wiring closet. That closet may refer to a floor with a cable between the floors. The main telecommunications closet contains pairs from the local telco. In the closets, you do the cross-connects. This is neither here nor there, but what it really stresses is order and neatness.

 

[Reloadron]

If you look at the RELAY-URM SERIES Universal Relay Module manual you will note that pins 2,5,8, and 11 are relay Common terminals for the 8 relay circuits. They are all tied to 12 volts heater power this is +12 volts. I labeled it 12 volt heater power in the drawing. Each relay output, the N/O (Normally Open) relay contact is connected to a heater. Subsequently each heater element is connected to 12 volt common. Now 12 volt heater power implies + and common implies - and I can't make in any more simple. Truth be known it really would matter not. A heating element does not care about polarity. A heating element could care less and the power could even be AC sans any + or - for that matter. The relay contacts are a switch, that is all they really are. They are either on or off depending on what the temperature controller tells them to be. Below set point the controller turns the relay on, it is in an energized state, the normally open contacts are closed and the system is calling for heat. Above set point the N/o contacts are open and no power is applied to the heating element.

Maybe another member can provide a better point to point wiring drawing and explain it better than myself.

Ron

 

[KeepItSimpleStupid]

The world that you are in matters.

Since your clueless: Red is a customary color for positive and black is a customary color for negative UNLESS your in the thermocouple world. A car battery uses red and black. A 9V DC battery clip uses black and red. Green or green with a yellow stripe is a typical ground color.

In the US, white is Neutral (which is connected to ground at one point) and black is hot in an AC system.

 

[curoi]

Okay, so here is what I managed to do. We have a 1000mA 12 VDC AC Adapter from radio shack. I believe the wiring of the adapter is such that the brown lined wire is positive and the white wire is negative. I ran the negative (white) wire of the adapter directly into COMM Relay 1 Pin 1 of the top output of the relay. I then ran the negative wire of the dimmer into N/O Relay 1 Pin 2 of the top output of the relay. Next I connected the positive end of the dimmer (and thus heater element) to the positive end of the AC adapter. I then connected the relay to the controller based on the schematic and the thermocouple was likewise connected to the controller as shown. Nothing happened though. The relay did not turn on and neither did the controller. Does the controller need to be powered separately with an AC current?

 

[KeepItSimpleStupid]

There has to be a voltmeter in your lab. Is there?

In many cases the ribbed or marked cord is negative, so I am concerned. You MUST know the correct polarity.

If you don't have a voltmeter, can you obtain an 1N4001 diode, an LED and 1K 1/2 Watt resistor. These would be availabe at radio shack. Would you have the means to solder these items together? (direction will matter)

I believe the relay box and the controller both require power of some sort.

The relay can only activate if the controller is conncectd to the relay bank and they are each powered (from what I remember).

 

[Reloadron]

Uh, you mention 10,000 mA which is 10 Amps? Please make sure of the current.

The controller should at least measure the temperatures if it is powered with 120 VAC? The controller will need set up and programmed per the manual also.

The relay box and controller should require 120 VAC power.

I see Kiss has also just posted.

Ron

 

[curoi]

The AC Adapter is a 12V 1000 mA adapter

 

[KeepItSimpleStupid]

Ron: Guess syou need to get your glasses checked?

 

[Reloadron]

Ron: Guess syou need to get your glasses checked?

Huh?

Seeing extra zeros in the AC/DC adapter from Radio Shack. Long day back at work. I had Jury Duty last week.

Anyway, I don't see this working for the heaters. What was driving the dimmers before? The dimmers are DC in and DC out correct? I assumed there must have been a large DC supply around somewhere? If each heater was only 12 watts that would be one amp per heater.

Next, when powered up exactly what does the controller do? Does it read the TCs?

Ron

 

[KeepItSimpleStupid]

Huh?

Okay, so here is what I managed to do. We have a 1000mA 12 VDC AC Adapter from radio shack.

Last time I checked 1000 mA is 1A. You must have been seeing to many zeros.

I'll bet 1 Amp is too small for all the heaters. Havn't heard any info yet on whether or not a voltmeter can be found or bought. About $4.00 at Harbor Freight if your hard up.

 

[curoi]

KISS,

We don't currently have a voltmeter in the lab or a soldering iron but I imagine I could get these relatively cheaply, right? Yeah, there are seven heaters in total. It takes about 1 amp to run one heater? With dimmers, are you suggesting that I reconnect the dimmer inputs and outputs directly to the power supply and then the V+(out) to the dimmer and V-(out) to the relay. This seems weird as only one wire will be connected the heater at all.

Reloadron,
It there a different power source I can use to wire to the relay so that all 7 heater elements can run on the same power source. (Perhaps a higher ampere AC adapter? - again, don't know much about circuits). As for the dimmers, I do believe they are DC in and DC out but I don't have the original packaging so I'll have to double check the link someone else posted. For the Pins 2, 5, 8, and 11 Common, must each of those heater. Also, nothings ever been powered on (including the controller because I do not have a power source for that yet, and the dimmers have never actually been hooked up to anything - they are just wired to the peltier pads (heaters).

 

[KeepItSimpleStupid]

Are these really peltier pads? If they are, they require a heat sink of some sort ( or water) on the opposite side of the pad. Peltier pads can heat and cool.

I am suggesting connecting the dimmer directly to the power supply (correct polarity, of course). We are guessing that 1 Amp may not be enough to run all the heaters.

IF you connect the output of the dimmer directly to the heater, you should be able to monitor the temperature and adjust the dimmer for the "sweet spot".

To use the controller as a temperature monitor, the TC must be hooked up and it must be powered.
To use it as a controller, they must be connected together through the open collector outputs to the relay contolller. The relay controller also needs power. So, if you "break" the positive connection of the dimmer to the heater and then attach the leads to the normally open contacts of the relay, you should be able to have control.

You need a meter for the lab. Find out what your budget is? A reminder is that you will not be able to measure power of the PWM output unless the meter is TRMS (True RMS). This may be worthwhile here.

This https://www.circuitspecialists.com/csi65-dmm.html?advancedsearch=true is one of the meters I have. It really isn;t that bad, but it's not TRMS.

Fluke and HP make very nice meters. They may be expensive and they may be subject to the "five finger discount".

Don't hook anything up unless you have the right polarity. You could do this with just a diode like a IN4001 (1Amp) or 1N5401 (3 Amp). The iN5401 is preferred.

You can insert the diode series with the output of the power supply (it doesn't matter which lead) that's connected to the dimmer. If the heater doesn;t work, then flip the wires from the output of the DC power supply. When the heaters work, it is the right polarity. The band of the diode will point in the positive direction. So if you follow the band toward the dimmer. It should point to V+ in. Mark the polarity of the DC supply and remove the diode.

 

[Reloadron]

Reloadron,
It there a different power source I can use to wire to the relay so that all 7 heater elements can run on the same power source. (Perhaps a higher ampere AC adapter? - again, don't know much about circuits). As for the dimmers, I do believe they are DC in and DC out but I don't have the original packaging so I'll have to double check the link someone else posted. For the Pins 2, 5, 8, and 11 Common, must each of those heater. Also, nothings ever been powered on (including the controller because I do not have a power source for that yet, and the dimmers have never actually been hooked up to anything - they are just wired to the peltier pads (heaters).

In my drawing I showed a single 12 volt DC power supply. The problem is I have no clue how much current those little heater pads draw. My example was a 12 volt 12 watt pad would draw 1 amp. Do you have any data at all on the pads?

Ron

 

[KeepItSimpleStupid]

I do think you should secure a multimeter: This does not seem too bad. **broken link removed** The frequency response of the TRMS option is out of spec for what you need, but the price isn't bad. I think the dimmer uses 1 kHz. At $100 it doesn't seem that bad.

Where things can get expensive is if the multimeter has temperature measuring options or has data-logging options.

I hope Ron has some better suggestions.