Control.com - Nerds in Control

Hello,

I'm reading a specification about control valve drives (http://www.auma.com). I have found something very interesting to me. In addition to limit switches that can signal open or closed status to the PLC, it also have possibility to signal torque open and torque closed switch.

I'm not sure how this is determined. For example if valve is opening and hit an obstacle on the way before it opens totally, it needs to signal torque open signal.

I wonder how this works? How drive's electronics can determine this state?

Thanks for the help.

Measuring and limiting torque is standard features with motorised valves used mostly for On-Off applications.
Sensing and limiting torque helps in two ways,
1. Protects valve internal and soft seats (if any) at end of travel.
2. Protects motor. Motor may have other protections as designed by different vendors.

Torque exerted by internal motor is proportional to "flux density" in stator winding and "current" drawn. Both are sensed internally by winding sensor/CT or equivalents. Electronic torque controller get both inputs to calculate actual torque and compare it with limit torque (set through configuration tools).

Once the actual torque is outside the limit, the motor is immediately (or may be with definite delay) tripped.

Depending on type and design of valve, opening and closing torque requirements may be different. Hence actuator of these MOVs have different setting possible to protect the valve both during opening or closing.

Regards.

Easy, current = torque.

Regards
cww

Check out the link below, Rotork specialize in valves with torque limit switches,

Regards
Roy

http://www.rotork.com/en