Ametek PMT 40, Руководство пользователя

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User Manual
10
FOR PROPOR RESET
CONTROLLERS
To start up manually
Open reset valve fully
by turning reset knob clockwise to stop. Note
controller action (direct or reverse). If direct
acting, set red pointer well below black pointer
and desired value. If reverse acting set red
pointer well above black pointer and desired
value. This will cause controller to put out full
output pressure. Adjust diaphragm control valve
opening by adjusting supply regulator. When
process is under control, note output pressure.
To switch to automatic
Shut reset valve by
turning reset knob counterclockwise to stop.
Move red pointer back toward desired value
until output pressure just drops. Restore supply
pressure. To correct valve, adjust red pointer to
be sure output pressure is brought to exact value
noted during manual control.
Tuning procedure for propor reset
controllers may now be followed. If instrument
is already tuned, reset valve may be set at
previously determined value.
FOR PROPOR RESET + RATE
CONTROLLERS
To start up manually
Open reset valve fully by
turning reset knob clockwise to stop. Open
rate valve fully by turning rate knob clockwise to
stop. Note controller action (direct or reverse).
If direct acting, set red pointer well below black
pointer and desired value. If reserve acting, set
red pointer well above black pointer and desired
valve. This will cause controller to put out full
output pressure. Adjust diaphragm control valve
opening by adjusting supply regulator. When
process is under control, note output pressure.
To switch to automatic
Shut reset valve by
turning reset knob counterclockwise to stop.
Move red pointer back toward desired value
until output pressure just drops. Restore supply
pressure. To correct valve, adjust red pointer to
be sure output pressure is brought to exact value
noted during manual control. Tuning procedure
for propor reset + rate controllers may
now be followed. If instrument is already tuned,
reset and rate valves may be set to previously
determined values.
TROUBLE SHOOTING
PROCESS
When it is indicated that the difficulties are in the process (by manual control method or other diagnosis),
a systematic check procedure is suggested. Following is a check list of some common process
difficulties.
1. In a pressure controlled process the pressure tap must be in a representative location and should not
tend to become air bound or water logged as these actions will tend to give erratic and erroneous
measurement which will in turn cause erratic control.
2. The control fluid should reach the control valve in sufficient quantity to maintain control. The
controlled media should be free of debris which could foul the control valve.
3. Steam traps must operate efficiently, not permitting back-up of condensate. If system is steam fed
and operating below 212°F (100°C) the condensate system must be designed for vacuum service.
Violent cycling will result when traps are not designed for vacuum service.
4. If process has a heat exchanger, the heat exchange surface must be adequate. It must not become
air bound or flooded. Foreign matter tending to accumulate should be cleaned periodically to prevent
excessive transfer lag.
CONTROL VALVE
1. Valve must be sized correctly. It should be large enough to maintain the process for most load
conditions. If it operates near the fully open position continually, it is probably undersize and does not
have sufficient controllability. If it operates near the closed position, it is probably oversize.
2. When large pressure fluctuations occur in control fluid, the valve should be of balanced construction