Yokogawa EJA438 - Manual (Page 47)

IM 1C22J1-01E 8-1
8. MAINTENANCE
8. MAINTENANCE
8.1 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 during draining condensate or venting
gas in transmitter pressure-detector section even
after dismounting the instrument from 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 disas-
sembly and reassembly procedures required for
component replacement.
Since the transmitters are precision instruments,
carefully and thoroughly read the following sections
for proper handling during maintenance.
IMPORTANT
• As a rule, maintenance of this transmitter
should be implemented in a maintenance
service shop where the necessary tools are
provided.
• The CPU assembly contains sensitive parts
that may be damaged by static electricity.
Exercise care so as not to directly touch the
electronic parts or circuit patterns on the board,
for example, by preventing static electrification
by using grounded wrist straps when handling
the assembly.
Also take precautions such as placing a re-
moved CPU assembly into a bag with an
antistatic coating.
8.2 Calibration Instruments Se-
lection
Table 8.2.1 shows the instruments required for calibra-
tion. Select instruments that will enable the transmitter
to be calibrated or adjusted to the required accuracy.
The calibration instruments should be handled carefully
so as to maintain the specified accuracy.
8.3 Calibration
Use the procedure below to check instrument operation
and accuracy during periodic maintenance or trouble-
shooting.
1) Connect the instruments as shown in Figure 8.3.1
and warm up the instruments for at least five
minutes.
IMPORTANT
• 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
on the high pressure side, 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
the vacuum pump.
2) Apply reference pressures of 0%, 50%, 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.