ML6984, ML7984 SERIES 4000 DIRECT COUPLED VALVE ACTUATORS
9
95C-10939—11
OPERATION
Each time actuator terminals T5 and T6 are (re)powered,
the microprocessor will cycle the valve through a full stroke
to calibrate its position. Any stroke between 1/2 in. (13
mm) and 1 in. (25 mm) will be divided into 30 equal steps.
Run time is proportional to stroke length and power supply
voltage. The actuator will also slow down as the valve
closes off the seat. The LED lights when terminals T5 and
T6 are powered, and flashes when the actuator is in motion.
T5 is connected to Terminal R in ML6984 and to Terminal
W in ML7984.
NOTE:
Initial calibration does not apply to ML6984
installed for 3-wire control or installed for 5-wire
control without the 272630D position feed-
back/auxiliary switch module. Span and start
positions will need to be set during controller set-
up. See ML6984 Operation 3-wire, below. ML7984
always conducts a self-calibration sequence when
(re)powering up.
ML7984 Operation
The microprocessor responds to the signal across the input
terminals based on the configuration DIP switch settings.
When correctly connected to the actuator, a control signal
between signal input terminals is converted to a digital run
time and compared to pulse counts from the first gear in
the gear train. When these counters are equal, the drive
motor and drive shaft are stationary.
As long as the value of the controlled medium remains at
the controller setpoint, the control loop circuit is in
balance, and the actuator does not run. When the
controller set point or controlled temperature changes, the
controller output voltage is changed, causing the counters
to differ. As the actuator moves in the direction to correct
the difference, the counters increment or decrement, and
stop the actuator when the input and gear counts agree.
At the end of the valve stroke, the actuator develops the
necessary force for positive valve close-off. The motor
stops automatically when the motor draws a
predetermined current which corresponds to a force level.
The digital counters are reset and calibrated at each end of
stroke.
Modulating actuators will automatically travel to the
position corresponding to analog input signal following the
self-calibration cycle.
CAUTION
Disconnect power supply before beginning
installation to prevent electrical shock and
equipment damage.
All wiring must comply with applicable local
electrical codes, ordinances, and regulations.
Make certain that the voltage and frequency of the
power supply correspond to the rating of the device.
DO NOT electrically operate the MLx984 actuator
before assembly to the valve because damage not
apparent to the installer may occur.
DO NOT connect 24 Vac between any ML7984
signal input terminals. DEVICE FAILURE WILL
RESULT.
NOTE:
1.
The ML7984 must be field configured with the
DIP switches which are located beside the ter-
minal block. See wiring diagrams for details.
Turn power off before setting any DIP switches.
2.
There is a 1.5 second delay in actuator
response to every signal change. This occurs to
screen out electrical noise.
3.
For proper operation, voltage on the T5 and T6
must not be less than 22 Vac or 24 Vdc during
running or force generating stages. Increase
transformer VA rating or use a model with better
regulation if voltage drops below 22 Vac when
the valve is closing off.
ML6984 Floating Operation, 5-Wire
The motor is controlled by a microprocessor. Connecting B
to R for 1/10 second or longer tells the microprocessor to
cause the actuator to drive upwards. Connecting W to R will
cause the actuator to drive downwards. For “floating”
control, the actuator will remain in the last position when
there is no connection to R.
At the end of the valve stroke, the actuator will develop the
necessary force for positive valve close-off. As forces are
developed, the current to the motor increases. The
microprocessor stops the actuator automatically when
motor current and force reaches the factory-calibrated
level.
NOTE:
There must be at least 1.5 second delay between
successive floating input signals. The actuator will
ignore floating signals during calibration cycle
and does not remember any pulses sent during
this period. The controller may need to run
through its own calibration cycle before use.
ML6984 Operation, 3-Wire
ML6984 may be installed like a conventional (non-
electronic) floating actuator. The interface electronics are
powered at the same time as the motor. Pulses must be at
least 100 ms long with a delay of at least 1500 ms between
pulses. When ML6984 is not powered between terminals
T6 and T5/R, self-calibration will not occur. The controller
must drive the valve through a cycle manually to calibrate
stroke to the controller.
