On Wed, 24 Nov 2004 23:20:56 +0000, Tim S wrote:

On Wed, 24 Nov 2004 23:01:02 +0000, Andy Hall wrote:

You can buy valve heads that do this made by Sauter, called thermal
drives. RS have them as part 328-8562 or less from ControlsCenter.

I've been using Sauter's motorised variety (AXM 117S) which work from 24v
ac or dc with a 0-10v control signal. THese fit on in place of the TRV
head and can be set to any open or closed position from a DAC. They work
quite effectively.

Something similar is called a thermo-hydraulic actuator? (Heater heats
liquid, moves rod to operate valve head). I was going along these lines
(Danfoss ones are about 15+VAT, but driven at 240VAC) until I
hit upon the idea of just centralising everything except the actual
thermostat transmitters.

Timbo


The thermal drives are effectively as you describe.

They can be controlled in a pseudo-analogue way by varying the power
duty cycle but it's not very accurate.

The motorised ones have a built in servo which periodically
recalibrates itself against the end stop. Thus the 10v dc voltage
gives quite accurate and repeatable results.

http://www.sauter-controls.com/pds/pds/indexe.html


I wanted to have genuine proportional control so went for this
approach.

If you wanted similar for your solution, Sauter do make similar valves
that are equivalents or similar function to heating zone valves but
again with analogue control. I believe they cost around £70 though
:-(



--

..andy

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