Solartron Mobrey 7828 - Mechanical Servicing & Time Period Trap

Maintenance 7828 Density Transmitter Technical Manual
6-4 78285000_AA
Fault Possible cause Remedy
7828 does not
communicate with
ADView
Power failure to 7828
Power supply to
RS485/232 converter
failed.
A and B Modbus
connections reversed
RS485/232 converter
failed, wired
incorrectly, or
connected the wrong
way round
Check power supply to 7828 and
converter; replace if necessary
Check wiring
Try another converter
ADView incorrectly
installed on PC
Re-install ADView
Incorrect Slave
address chosen for
7828
Check slave address
RS232 port on PC
failed.
Connect to another free RS232 port
on the PC, if available.
Alternatively connect a known
working RS232 device to the PC to
check that the port is working.
6.3.1 MECHANICAL SERVICING
This mainly comprises the cleaning of any deposition or corrosion from the tines.
Deposition is removed by the use of a suitable solvent. For corrosion, solvent and the
careful use of a fine abrasive will usually be sufficient. However where extensive
corrosion has been treated, it is highly recommended that a full calibration is carried out to
check the transmitter characteristics.
CAUTION: Care is essential in handling the transducer during transit, installation,
and removal from the pipeline/tank.
6.3.2 TIME PERIOD TRAP
Disturbances in the fluid caused by bubbles, cavitation or contaminants can cause sudden
changes in the measured output, which may, under some circumstances, give rise to
instability (i.e. hunting) in a control system relying on the measurement. The 7828 can
maintain the analog output during such perturbations by ignoring the aberrant
measurement, and maintaining the output at the last good measured value. This facility is
known as the Time Period Trap (TPT).
Under all normal circumstances, the factory settings for the TPT should be used.
However, in extreme cases it may be necessary to alter the settings to meet the demands
of a particular system. This should only be done after monitoring the behaviour of the
system for some time, to establish the normal running conditions.