Maintenance - Emerson Fisher 546NS Instruction Manual

Instruction Manual
D103425X012
The output decreases until the diaphragm assembly is forced back to its original position and the exhaust port is closed
again. The reduced pressure in the feedback bellows diminishes the force to return the armature to the equilibrium
position.
Figure 6 shows output‐time relationship curves for loading and exhausting an actuator. Exhausting times are
nominally 25 percent of the loading times.
Figure 6. Output‐Time Relationship
100
90
80
70
60
50
40
30
20
10
0
0 10 20
19A1361‐A
A3103
Reverse‐acting transducers operate in a similar manner except that when the DC input signal increases, the output
pressure from the relay decreases. Conversely, a decreasing input signal increases the output pressure.

Maintenance

Maintenance of the transducer consists of relay and feedback bellows replacement.
WARNING
The following maintenance procedures require that the transducer be taken out of service. This requires that certain
precautions be taken to avoid personal injury or equipment damage caused by sudden release of pressure. Prior to
maintenance:
D Always wear protective clothing, gloves, and eyewear when performing any maintenance procedures to avoid personal
injury.
D Disconnect electrical power before removing the transducer cover.
D Shut off or disconnect pressure lines to the transducer.
D Disconnect any operating lines providing air pressure, electrical power, or a control signal to the actuator. Be sure the
actuator cannot suddenly open or close the valve.
D Use bypass valves or completely shut off the process to isolate the valve from process pressure.
D Do not remove the actuator from the valve while the valve is still pressurized.
D Relieve process pressure on both sides of the valve.
D Vent the power actuator loading pressure and relieve any actuator spring precompression.
D Use lock‐out procedures to be sure that the above measures stay in effect while you work on the equipment.
D Check with your process or safety engineer for any additional measures that must be taken to protect against process
media.
LOADING
EXHAUSTING
30 40 50 60 70 80
TIME (%)
100
90
546NS Transducer
June 2021
15