9
Operation
DO NOT use this product outside the recommended operating pressure,
temperature and other specification ranges. Improper use may result in
such hazards as damage to the product or malfunctions which may lead
to serious accidents. Local regulations may restrict the use of this product
to below the conditions quoted.
Take measures to prevent people from coming into direct contact with
product outlets. Failure to do so may result in burns or other injury from
the discharge of fluids.
Installation, inspection, maintenance, repairs, disassembly, and adjustment should
be done only by trained maintenance personnel.
1. Checking and adjusting zero and span in electropneumatic actuators
Adjustment may only be carried out when the actuator is mounted on the valve!
Zero and span are adjusted to determine the starting point and the upper range
value of the actuator.
When the control signal (reference variable) changes from 4 to 20 mA, the valve
must correspondingly pass through its entire travel range from 0 to 100 %.
Zero adjustment is always based on the closed position of the control valve.
Actuator with close fail-safe action "Air to open", zero (starting point) must be
adjusted to 4 mA and the upper range value to 20 mA.
Whereas a globe valve assuming an open fail-safe position (Air to close), requires
adjustment to be the other way round. That is, zero must be adjusted to 20 mA and
the upper range value to 4 mA.
Zero and span of the electropneumatic actuator are adjusted to rated travel by the
manufacturer.
Air to open type
Air to close type
Fig. 4
Potentiometer for span (1)
Protective cap
Zero adjuster (4)
Jumper (2)
Cover plate (3)
Zero adjuster (4)
