Solartron Mobrey 7828, Technical Manual

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7828 Density Transmitter Technical Manual Maintenance
78285000_AA
6-3
6.3 FAULT ANALYSIS AND REMEDIAL ACTION
A fault may be categorised as either an erratic reading or a reading which is outside limits.
Electrical faults can also cause symptoms which appear to affect the readings and it is
recommended that the electrical system is checked first, before removing the transmitter
for servicing.
Fault Possible cause Remedy
Readings fluctuate
slightly, i.e., are
noisy
Analog output
averaging time not
long enough Increase the averaging time using
ADView’s Board Configuration
facility (see section 4).
Erratic readings Gas bubbles around
tines
Cavitation
Severe vibration
Severe electrical
interference
Large amount of
contaminants
Remove primary cause; e.g.:
- install air release units to release
gas;
- apply back pressure to
discourage formation of bubbles;
- remove cause of vibration
Alternatively, it may be necessary to
adjust the Time Period Trap (see
section 6.3.2)
Readings outside
limits
Deposition and/or
corrosion on the tines. Clean tines (see section 6.3.1)
Analog output = 0mA No power to analog
output
Analog output circuit
failure
If voltage across pins 5 and 6 is not
15 to 28V, replace power supply.
Use ADView’s facility to set the
analog output to 4, 12 or 20mA (in
Board Configuration) to check
whether the output is functioning. If
not, replace circuit boards.
Analog output is 2mA Alarm condition
caused by lack of
power to 7828
Alarm condition
caused by other
internal failure
If voltage across pins 1 and 2 is not
20 to 28V, check and replace main
power supply.
Use ADView Diagnostics to check
that phase locked loop is in lock.
Temperature
readings incorrect
If other readings from
7828 are correct (i.e.
analog output and
Modbus appear to be
functioning correctly),
the temperature
sensor has probably
failed. Return the transmitter to Solartron
for servicing.