MDE142E0
12/60
06/04/04
4.2. General function
4.2.1.
Selection between turn clockwise to close or anti-clockwise to close
Via local operator interface it is possible to select between the following: “actuator turn CLOCKWISE or stem OUT
for linear actuator, (CW/OUT) to close” or “actuator turn counter clockwise or stem IN for linear actuator
(CCW/IN) to close”.
4.2.2.
Stroke limit electronic setting
The stroke limits of the hydraulic linear actuator are performed by means of the local interface operator (see relevant
paragraph). This operation must be done after the mechanical setting.
4.2.3.
Open loop operation
A local 3 position selector switch (
Local/Off/Remote
), of the local operator interface, permits the opening of the
position control loop and the direct control of the actuator through local
Open/Close/Stop
commands (MANUAL
mode). The STOP command is always available , both in LOCAL and ins REMOTE
4.2.4.
Direct / Reverse action
The configurable Direct/Reverse action parameter, allows to choose the action of the position regulator in function
of the position request signal.
If direct action was configured, the 4 mA position request signal corresponds to closing request and the 20 mA
corresponds to opening request.
Vice versa if reverse action was configured, the 4 mA signal requires opening and the 20 mA requires closing.
The Direct / Reverse parameter does not affect the 4-20 mA position re-transmission signal. In fact, 4 mA
corresponds always to closed position and 20 mA to open position.
4.2.5.
Position failure (Jammed)
If the
error of
position (difference between ‘’
present position
’’ and ‘
’internal
position request
’’) is greater than
4 %, but the position value does not change within a configurable time, an automatic cut-off of the control circuit
occurs and an alarm is set. The time can be configured at a value from 1 to 250 sec. The control is active when the
MCU works in REMOTE (AUTO).
4.2.6.
Opening high speed operation
When the 4-20 mA signal
(REQ)
change from low to higher value with a variation speed higher than 32 mA/sec (for
minimum 3,2 mA) , the MCU energise a third solenoid valve which allows that the pilot valve opens, discharging
quickly the cylinder chamber pressure. In this condition the actuator speed reaches a speed of 180°/sec. As soon as
the actuator position reaches 90% opening, the high speed solenoid valve is de-energised, the operating speed slow
down and the movement is controlled by the positioner solenoid valve until the new requested position.
4.2.7.
ESD operation
When a dry contact, in the control room, opens (see option D1 of the SE89B-173A terminals C4-C1) the actuator, is
configured to override any existing command and drives the valve to the fully open in 6-7 sec
4.2.8.
Internal temperature monitoring
The system are designed to work from -30° C to 60 °C.
If the internal temperature is greater than 80°C or lower then -35°C, a warning is set.
If the internal temperature is greater than 90°C or lower then -40°C, an alarm is set. .
4.2.9.
Accumulator nitrogen leakage
The actuator is provided with a pressure switch that contact opens when the hydraulic pressure drop down to an
adjustable pressure threshold. The pressure threshold should be set at least 5 bars below the minimum pressure fixed
by the “adjustable relief valve” (see par. 5.3).
The pressure switch contact is read by the MCU that switches on the hydraulic pump electrical motor. When the
pressure is increased of about 10 bars the pressure switch contact closes.
The MCU measures the time between the opening and the closing of the pressure switch contact .
If the time is 50% lower than the variable “N2 REF TIME ” a “ LOW N2 “ warning, is send to advise that the
Nitrogen leakage ( N2 ) is occurred.
The measure is performed only if the local selector is in REMOTE, the hydraulic pump motor is “on” and the
position request signal (REQ)remains constant.
