12
7 NE 72 en
8.3
Replacement of the diaphragms
Remove the spring (40) and loosen the screws (23). Remove
the zero adjustment wheel, the screw (15) and the nut (16).
Replace the diaphragms (13, 14). See Fig. 16. Note the
installation position of the diaphragms convolution.
Check during assembly that the large O-rings (11,12) and
the small ones (18, 19, 20, 21) are in place. Check the condi-
tion of the gasket (55) and secure the nut (16) with Loctite
242. Fasten the zero adjustment wheel (61). Tighten the
cover screws (23) evenly. Check the positioner adjustment
after replacing of diaphragm.
Note:
O-rings (11, 12) in the old construction only (manu-
factured before 12/94).
8.4
Force coil-nozzle assembly
Repairing of the force coil-nozzle assembly requires good
knowledge, workmanship and special tools.
It is highly recommended to replace a faulty assembly with
a new one.
Handle and disassemble the coil-nozzle assembly in the
cleanest and most dust-free surroundings possible.
8.4.1
Removing the force coil-nozzle
assembly
1. Disconnect the signal wires from the terminal.
2. Remove the springs (40, 41) and loosen the terminal
screws (36). Remove the terminal card (35).
3. Hold on to the assembly and loosen the screws (38) in
the back wall of the case.
8.4.2
Cleaning the magnet air gap
1. Remove the fastening screw (169) of the magnet (168)
and lift the magnet carefully out of the body. Clean the
magnet air gap with e.g. tape.
2. Place the magnet into the body carefully, making cer-
tain that the moving force coil does not jam in the air
gap. Tighten the screw (169) firmly.
8.4.3
Mounting the force coil-nozzle
assembly
Check the O-ring (39) in the case and the location of the
wire in the body groove. Turn the screws (38) until tight.
Mount the terminal card and the springs. Note the correct
position of the spring (40), see Section 4.3. Check the
adjustment.
8.5
Changing the restriction assembly
Loosen the screw (25) to remove the restriction assembly
(24). A blocked restriction and/or filter can be cleaned if
needed. Replacing the whole assembly is althoug recom-
mended.
9
TROUBLESHOOTING
9.1
Electrical defects
1. The electrical condition of the positioner can be measu-
red in the field in line without shutting down the appara-
tus. There are measurement terminals, see Figs. 7 and 8,
for voltage (U) and current (I) on the terminal card. Pull
out the jumper before taking the measurement. Note the
correct polarity of the meter.
2. Current and voltage measurements can be used to
determine whether the signal line and the electrical
components of the positioner are in order.
Fig. 15
Replacement of diaphragms
NOTE:
gap required
Fig. 16
Restriction assembly (24)
Table 6
Current and voltage measurements
Measurement
Possible faults
U (V)
I (A)
0
(—)
Signal wire polarity wrong
No
No
Signal wire defect.
Wire not connected to terminal
>4
When
I=20 mA
Coil connection wire or coil winding
defect.
Shunt resistance defective
0
Yes
Coil or shunt resistance short circuited
filter
gasket
restriction ø 0.3
