Yokogawa EJX930A - Manual (Page 53)

<9. Maintenance>
9-1
IM 01C25R01-01E
9. Maintenance
9.1 Overview
WARNING
Since the accumulated process fluid may be
toxic or otherwise harmful, take appropriate care
to avoid contact with the body or inhalation of
vapors when draining condensate or venting gas
from the transmitter pressure-detector section
and even after dismounting the instrument from
the process line for maintenance.
Maintenance of the transmitter is easy due to its
modular construction. This chapter describes the
procedures for calibration, adjustment, and the
disassembly and reassembly procedures required
for component replacement.
Transmitters are precision instruments. Please
carefully and thoroughly read the following sections
for information on how to properly handle them
while performing maintenance.
IMPORTANT
• As a rule, maintenance of this transmitter
should be done in a shop that has all the
necessary tools.
• The CPU assembly contains sensitive parts
that can be damaged by static electricity.
Take precautions such as using a grounded
wrist strap when handling electronic parts or
touching the board circuit patterns. Also be
sure to place the removed CPU assembly
into a bag with an antistatic coating.
9.2 Calibration Instruments
Selection
Table 9.1 lists the instruments that can be used
to calibrate a transmitter. When selecting an
instrument, consider the required accuracy level.
Exercise care when handling these instruments to
ensure they maintain the specified accuracy.
9.3 Calibration
Use the procedure below to check instrument
operation and accuracy during periodic
maintenance or troubleshooting.
9.3.1 Pressure and Static Pressure.
1) Connect the instruments as shown in figure 9.1
and warm up the instruments for at least five
minutes.
IMPORTANT
• Do not perform the calibration procedure
until the transmitter is at room temperature.
• To adjust the transmitter for highest
accuracy, make adjustments with the
power supply voltage and load resistance
including leadwire resistances set close to
the conditions under which the transmitter is
installed.
• If the measurement range 0% point is
0 kPa or shifted in the positive direction
(suppressed zero), the reference pressure
should be applied as shown in the figure.
If the measurement range 0% point is shifted
in the negative direction (elevated zero), the
reference pressure should be applied using
a vacuum pump.
2) Apply reference pressures of 0%, 25%,
50%, 75%, and 100% of the measurement
range to the transmitter. Calculate the errors
(differences between digital voltmeter readings
and reference pressures) as the pressure is
increased from 0% to 100% and is decreased
from 100% to 0%, and confirm that the errors
are within the required accuracy.