Strange thermostat that monitors fin pipe--how does it work?

[Otto Barz]

A room branch of my hot water fin pipe heating system is controlled by a wall-mounted rotating dial thermostat that is connected directly to the fin pipe. They are connected together by a single bare wire that is very thin and flexible. The wire is not a dual wire, but exactly as described, single and bare, very flexible, and seems nothing like would be an electrical conductor. How does the wire operate to tell the valve controller (the device on the finpipe?) to close or open the valve? I need to shorten that wire.

 

[MicEd69]

That "wire" is a thermocouple, and it is not a "single bare wire". It is a very small copper tube with another wire of different material inside the tube. The two wires are connected together at the end of that copper tube. The temperature at the end of that tube results in a voltage being generated at the juncture of the two metals that is measured in your thermostat, which in turn controls the flow to your radiator.

Why do you "need" to shorten the thermocouple? Thermocouples are often coiled up and placed in an out of the way space. But I'm afraid you cannot shorten the thermocouple.

 

[Otto Barz]

Thanks very much for the feedback, Ed!

About half the diameter of the wire used for a paperclip (and way more flexible), I'm amazed to think that it's a copper tube with something inside of it. Also, the wire is silver, not copper-colored. Is it still a thermocouple?

While I could coil it rather than shorten it, the purpose in containing it is that it is going to be put inside of new cabinetry where its earlier length is no longer needed. If I had to guess, I'd say it is presently about 6-8 feet long.

For context, I'm attaching a photo that shows the wires and their attachment to the valve controllers.

Thanks again for your very helpful feedback,
Otto

 

[Otto Barz]

Trying again to see if anyone knows what this is and how it works. Looking at other thermocouples, it doesn't appear that a thermocouple can be contained within a wire this thin. What is this device? More importantly, how does the wire transmit information?

 

[BlueSkyHigh]

Thermocouples transmit "information" via exhibiting a change in resistance per a change in temperature. It's up to the receiving equipment to decipher what it means and what to do with it.

 

[MicEd69]

Is the "wire" a solid wire or does it look braided. I can't tell from the picture.

In any case, I cannot imagine that it is a single solid wire, but rather a very thin tube with a very small thin wire inside it.

Could you provide a closer picture of the wire and the insides of the devices if there are covers that you can remove? Do you have the name of the manufacturer of these units or model number of the system?

 

[Otto Barz]

Is the "wire" a solid wire or does it look braided. I can't tell from the picture.

In any case, I cannot imagine that it is a single solid wire, but rather a very thin tube with a very small thin wire inside it.

Could you provide a closer picture of the wire and the insides of the devices if there are covers that you can remove? Do you have the name of the manufacturer of these units or model number of the system?

It's a solid wire. It feels like it's aluminum. It's less than 1/32 of an inch in diameter--less than half the thickness of thin paperclip wire. I've included another picture. There are two such units in the setup. The wire extending to the right that appears to be coming out of the gray part of the valve is actually the wire from the second valve that can't be seen in the picture. I've also attached a picture of the wall-mounted thermostats. There are no nameplates anywhere and I'm afraid to fuss with any disconnections for fear that I won't get them back together again.

 

[MicEd69]

Again, I cannot imagine that a single wire can do anything but perhaps to ground a device. I assume that the wall thermostats do not have any wires coming from the wall side, correct? You really need to remove the cover from the thermostat or the device on the pipe to see where the wire(s) connect. Thermocouple wires can be very small. They can pass through the eye of a needle. LOL.

 

[Otto Barz]

We certainly agree on all counts, which is what prompted me to put this question onto the forum. A single wire can pretty much do two things: serve as a ground, as you point out, or create a short!

This particular "wire" simply cannot be a tube, which it must be if it is to contain the two-way flow of a thermocouple.

There is only one wire, the one I've been talking about, that comes out of the wall thermostat. You can see it come out of the bottom of each thermostat in the picture.

I've placed a query with the plumbers that installed the device about fifteen years ago. I may have a shot at getting a definitive answer from them. If I do, I will be certain to share it with you here.

Thanks for all your help so far,
Otto

 

[MicEd69]

I will be certain to share it with you here.

Please do, this has my curiosity at its peak!

 

[Otto Barz]

For sure!

 

[Otto Barz]

Finally, I have discovered what we are dealing with:

The information you provided seems to be a description of a remote temperature adjuster, the Danfoss RA 2000 with part number RA 013G8562 or RA 8562. Here's a breakdown of the details:

• Model: RA 2000
• Application: Remote temperature adjuster
• Temperature range: 46 °F - 82 °F (8 °C - 28 °C)
• Sensor type: Remote mounted sensor and dial
• Capillary tube length: 6 ft (1.8 m)
• Part number: RA 013G8562, RA 8562

This remote temperature adjuster is likely used in conjunction with a heating system, allowing you to control the temperature in a room by adjusting the dial on the sensor unit. The liquid-filled capillary tube transmits the temperature information to the valve body, regulating the flow of hot water to the radiator.

Is there anything specific you'd like to know about the RA 2000 or its functionality?

How does the capillary tube work?

The capillary tube in the RA 2000 remote temperature adjuster works based on the principle of friction and the expansion of a liquid with temperature. Here's a breakdown of its function:

1. Filled with Liquid: The capillary tube is filled with a specific liquid that expands and contracts depending on the surrounding temperature.
2. Pressure Change: As the temperature near the sensor increases, the liquid inside the capillary tube expands. This expansion creates pressure within the small confines of the tube.
3. Transmission to Valve Body: The pressure change in the liquid is transmitted through the capillary tube to the valve body of the RA 2000 unit.
4. Valve Adjustment: The valve body is designed to respond to the pressure changes from the capillary tube. As the pressure increases (due to rising temperature), the valve adjusts to restrict the flow of hot water to the radiator, reducing the heating in the room.
5. Reverse Effect: Conversely, when the temperature drops, the liquid in the capillary tube contracts, lowering the pressure. This signals the valve body to open up more, allowing increased flow of hot water to the radiator and raising the room temperature.

In essence, the capillary tube acts as a long, narrow pressure sensor that translates temperature changes near the sensor into mechanical adjustments at the valve body, controlling the flow of hot water based on your desired temperature setting.