Ashcroft 4480 - Pneumatic Transmitter - Manual (Page 8)

8
GeneraI
Many complaints of faulty transmitter operation have, on
investigation, proven to be due to faulty installation. For this
reason, the following possible causes of trouble should be
considered whenever trouble develops after a new installa-
tion or change in conditions:
Note: To facilitate maintenance and adjustment, the trans-
mitter should be mounted to provide easy access.
a. In critical installations where the pressure tap is at a
different elevation from the transmitter, correction
must be made for liquid “head” or ‘’leg.”
b. Supply air should be filtered and dried.
c. Supply air pressure should be within the specified
ranges.
d. The transmitter should be mounted vertically, to
ensure correct action of components and to maintain
calibration position. If angular mounting is necessary,
the transmitter should be recalibrated in the position
to be used, in order to ensure maximum accuracy.
e. Extremes of ambient temperature should be avoided.
The transmitter should not be subjected to tempera-
ture above 150°F. If process temperatures exceed this
limit, protect the transmitter by means of a siphon or
diaphragm seal.
Note: Since most pressure take-offs are dead end service,
with resultant cooling, it is unlikely that the transmitter
itself will be subjected to temperatures exceeding
150°F, except in extreme cases.
f. If very low temperatures are encountered, care must
be taken to eliminate any possibility of moisture in the
air lines.
g. For all installations, both the transmitter and the
receiver should be checked together, as a unit, before
operation.
Troubleshooting Procedures
To assist in correcting installation or operational deficiencies,
refer to the following listing of possible troubles and suggest-
ed corrective actions
CAUTION
Dash pot is air actuated. Do not use oil.
TROUBLE CORRECTIVE ACTION
1. Pulsation at receiver. 1. Check output line from transmitter to receiver for leaks. Tighten all faulty connections;
repair or replace defective tubing.
2. Remove hex cap on relay and clean seat and seat valve, removing any dirt or foreign
matter which may have entered from air lines.
3. Check for contact between vane and nozzle. Bend vane slightly to center It between
nozzles.
2. Pulsation at input to transmitter. 1. Install pulsation dampener or needle valve slightly ahead of bourdon tube, throttling down
the dampener or valve until pulsation stops but still maintaining an opening in
the line.
3. Vibration on transmitter panel. 1. Brace or shock-mount the transmitter as necessary. Vibration should be eliminated insofar
as possible to prevent loss of calibration of the transmitter.
4. Loss of calibration. 1. Check for and eliminate severe piping strains. (Note: Ashcroft transmitters are designed
and constructed to eliminate normal piping strains.)
2. Check for and eliminate wedging between base casting and plate by screws, nuts, or
other foreign objects.
5. Receiver not corresponding 1. Check for and eliminate leaks in output line.
to transmitter. 2. Check for and eliminate foreign matter in output line.
3. Check to be certain that transmitter is connected to proper receiver.
6. Gross non-linearity in output. 1. Check for interference which may be compressing tubing from relay to input nozzle.
Position tubing to prevent interference.
2. Check for lack of contact between flexure assembly and adjusting disc. Replace flexure
assembly if not in contact with disc.
TROUBLESHOOTING
I&M008-10061-1-01 250-1969-C_I&M008-10061-1/01 250-1969-C 12/20/13 9:09 AM Page 8