Thermal Valve Actuator

[BigCheese]

Hello,
I'm using one of these Thermal valve actuator's in my project:
http://www.sauterautomation.co.uk/sal/en/products/electric_drives__control_valves__butterfly_valves/unit_valves_and_drives/therm__drive_f__unit_valves__w__stroke_ind_.html (I'm using the AXT111F202 which is 24V.)

At the moment I've got a circuit built that will fully open and close the valve using a mosfet, but I'm not sure how to program it so that the valve stays only partially open.

Please explain to me the best way to be able to control how much this valve opens.

Thankyou

Edit: I probably should have mentioned that I'm using an 18X, and the valve is connected to output 3.
Edit 2: What's up with the "Join date: Jan 1970" on the forum?

 

[papaof2]

I've never used one of these valves, but the data sheet indicates that its possible to get partial opening by pulsing the input signal.

"With a &#8216;pulse-pause&#8217; clock signal, which effects a periodic open/close position, a quasi-continuous control system can be achieved with a cycle duration of 4 minutes. Permissible cycle duration: either < 4 min or > 12 min. Using the auxiliary contacts (which are available as an accessory and can be fitted later), a circulation pump or a heat counter, for instance, can be switched on."

I would think that you need to apply power for some minimum period to get the expanding bulb hot enough to start movement, then apply pulsed power to control the temperature to increase/decrease the valve opening. This is a place for PWM to the MOSFET. Search for
pwm* mosfet
to get designs that you could adapt.
(pwm* to get around the "must have 4 characters or more" requirement in the search tool)

A 50% duty cycle may not give 50% opening of the valve - this is something you will have to test.

John