Checkout - Honeywell ML7421A Product Data

Actuator Override
The converter output signal override function can be used in
freeze protection or similar applications. It forces the actuator
to a specific position, overriding the control signal. To exercise
this function, disconnect the 24 Vac common from the
actuator (T2) and connect it to Terminal O1 or O2. Connecting
to Terminal O1 fully extends the actuator stem (bottom stem
position). Connecting to Terminal O2 fully retracts the actuator
stem (upper stem position).
The control signal (+) is ignored when the override signal is
applied to Terminal O1 or O2. This override can be achieved
with a switch or relay. See Fig. 12.
ML7421A,B
WIRING
STRIP
T1
T2 –
+
+
O1
O2
R1
W1
B1
POWER SUPPLY. PROVIDE DISCONNECT MEANS
1
AND OVERLOAD PROTECTION AS REQUIRED.
2
0 TO 10 OR 2 TO 10 VDC CONTROL SIGNAL
(DEPENDING ON ACTUATOR MODEL).
3 SEE OVERRIDE SECTION FOR DETAILS ON
OVERRIDE OPERATION.
Fig. 12. Connections for overriding the control signal to
drive the actuator to a specific position.
Direction of Action
The direction of action can be changed by repositioning the
Selector Switch S1 on the component side of the printed
circuit board (see Fig. 11) for the 0 to 10 Vdc models only
(ML7421A1024 and ML7421B1015). It is factory set so the
stem extends (bottom stem position) at increasing signal and
retracts (upper stem position) at decreasing signal.
The 2 to 10 Vdc models (ML7421A1008 or ML7421B1007) are
not furnished with a selector switch. Reverse the operation of
these actuators by reversing the signal from the controller.
L1
(HOT)
L2
1
2
OUTPUT
SP3T
OVERRIDE
SWITCH
3
M6751-1
ML7421A,B ELECTRIC LINEAR VALVE ACTUATOR

CHECKOUT

The ML7421 Electric Linear Valve Actuator can be checked
out either directly or using a controller.
Direct Checkout
Mount the actuator for the required application.
Check the valve position and make sure that 24 Vac is
correctly applied to the actuator.
Apply the control signal to the appropriate leadwires to
move the valve in the required direction.
If the actuator does not move, make sure the actuator
is properly installed.
If the actuator is correctly installed and still does not
run, replace the actuator.
Controller Checkout
Adjust the setpoint of the controller to call for opening
or closing the valve. Observe the actuator.
If the valve is closed, it should begin to open.
If the valve remains closed, move the setpoint further
toward the open setting.
If the valve still does not move, check for 24 Vac in the
actuator power input.
If 24 Vac is present and the actuator does not operate,
reverse the controller leadwires to determine if the
device is miswired.
If the wiring is correct, 24 Vac is present on the power
input terminals and the actuator does not run, replace
the actuator.
7
63-2517—1