Yokogawa EJX930A - Manual (Page 51)

<8. Operation>
8-4
IM 01C25R01-01E
8.3 Starting Operation
After completing the zero point adjustment, follow
the procedures below to start operation. Steps
1) and 2) are specific to the differential pressure
transmitters.
1) Close the equalizing valve.
2) Gradually open the low pressure stop valve.
This places the transmitter in an operational
condition.
3) Confirm the operating status. If the output
signal exhibits wide fluctuations (hunting) due to
periodic variation in the process pressure, use
the communicator to dampen the transmitter
output signal. Confirm the hunting using a
receiving instrument or the integral indicator,
and set the optimum damping time constant.
4) After confirming the operating status, perform
the following.
IMPORTANT
• Remove the communicator from the terminal
box, and confirm that none of the terminal
screws are loose.
• Close the terminal box cover and the
amplifier cover. Screw each cover in tightly
until it will not turn further.
• There are two covers that must be locked
on the ATEX Flameproof type transmitters.
An Allen head bolt (shrouding bolt) under
the edge of each cover is used to lock the
cover. When the shrouding bolt is driven
counterclockwise with an Allen wrench, the
bolt rotates upward and locks the cover. (See
section 9.4.) After locking the covers, confirm
that they are secure and cannot be opened
by hand.
• Tighten the zero-adjustment cover mounting
screw to secure the cover.
8.4 Shutting Down the
Transmitter
Shut down the transmitter as follows.
Steps 2) and 3) are specific to the differential
pressure transmitters.
1) Turn off the power.
2) Close the low pressure stop valve.
3) Open the equalizing valve.
4) Close the high pressure stop valve.
5) Close the high pressure and low pressure tap
valves.
NOTE
• Whenever shutting down the transmitter for a
long period, remove any process fluid that is
in the transmitter pressure-detector section.
• The equalizing valve must be left OPEN.
8.5 Venting or Draining
Transmitter Pressure-
detector Section
Since this transmitter is designed to be self-
draining and self-venting with vertical impulse
piping connections, neither draining nor venting
will be required if the impulse piping is configured
appropriately for self-draining or self-venting
operation.
If condensate (or gas) collects in the transmitter
pressure-detector section, the measured pressure
may be in error. If it is not possible to configure the
piping for self-draining (or self-venting) operation,
you will need to loosen the drain (vent) screw on the
transmitter to completely drain (vent) any stagnated
liquid (gas.)
However, since draining condensate or bleeding off
gas disturbs the pressure measurement, this should
not be done when the loop is in operation.
WARNING
Since the accumulated liquid (or gas) may be
toxic or otherwise harmful, take appropriate care
to avoid contact with the body, or inhalation of
vapors.