West Control Solutions Pro-EC44 - Manual (Page 35)

Pro-EC44 2-Loop Graphical Profile Controller & Recorder
Pro-EC44 Product Manual - 59540-1 October 2013 Page 28
Special Wiring Considerations for Valve Motor Control
Valve Motor Drive (VMD) controllers require two identical outputs to be assigned to position
the valve. One to open and one to close the valve. These outputs can be two single relays,
two triacs, two SSR drivers or one dual relay, but it is recommended to use two single relays
(SPDT change-over contacts), and to interlock the relay wiring as shown. This prevents both
motor windings from being driven at the same time, even under fault conditions.
Switching actuators directly connected to the valve motor must only be used up to half of
their rated voltage (see
CAUTION below). The internal relay and triac outputs are rated at
240VAC, so the maximum motor voltage when using them in this way is therefore 120V
unless interposing relays are used. Interposing relays or other devices used to control the
valve must themselves be rated for twice the motor supply voltage.
Figure 42. Interlocking of Valve Motor Drive Relays
CAUTION: The windings of a valve motor effectively form an
autotransformer. This has a voltage doubling effect when power is applied
to either the Open or Close terminal, causing twice the supplied voltage at
the other terminal. For this reason, switching devices directly connected to
the valve motor must only be used up to half of their rated voltage. The
maximum motor voltage when using the internal relays/triacs is therefore
120V unless interposing relays are used. Interposing relays or other devices
used to control the valve must themselves be rated for twice the motor
supply voltage.
Open Valve Winding
Close Valve Winding
Valve Common
“O
P
E
N”
RE
L
AY
N/O
C
N/C
N/C C N/O
“CLOSE” RELAY
N/C C N/O
120VAC SUPPLY
2 x 120V = 240V
120V