Valve actuators not operating correctly with a SE8000 room controller

Issue

When proportional 0-10Vdc type valve actuators are used with a SE8000 room controller, the actuators behavior is inconsistent.

Product Line

SmartStruxure Lite

Environment

SE8300

SE8350

SE8600

SE8600

Cause

Some valve actuators e.g. wax filled (thermic type) have a high input impedance e.g. 100 Kohms. When connected to a SE8000 room controller, the actuators operation may be sluggish or may never operate.

The SE8000 has a maximum output of 5mA when set to proportional control, using actuators with high impedance, the SE8000 room controller fails to recognise there is an actuator and does not drive it.

Resolution

A burden resistor can be fitted to draw some current from the SE8000 room controller because the actuator's impedance is too large.

The burden resistor needs to be large enough not to affect normal use, but small enough to draw a current from the SE8000 room controller.

Using ohms law:

Valve actuator @ 100 Kohm

SE8000 UO output is 5 mA, maximum Vdc output is 10 Vdc.

Minimum size of burden resistor: 10 Vdc/5 mA = 2 Kohm.

It may be necessary to increase the size of the burden resistor e.g. 10Kohm.

The burden resistor is then installed between the signal ground and the signal, either at the controller or the actuator end.

Test the actuators for correct operation.