Yokogawa EJA115 - Manual (Page 33)

IM 01C22K01-01E 7-3
7. OPERATION
7.3 Starting Operation
After completing the zero point adjustment, follow the
procedure below to start operation.
1) Open the stop valve on the upstream side.
2) Gradually open the stop valve on the downstream
side. 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 BT200 to
dampen the transmitter output signal. Confirm the
hunting using a receiving instrument or the integral
indicator, and set the optimum damping time
constant. See Subsection 8.3.3 (3), “Damping Time
Constant Setup.”
4) After confirming the operating status, perform the
following.
IMPORTANT
• Remove the BT200 from the terminal box, and
confirm that none of the terminal screws are
loosened.
• Close the terminal box cover and the amplifier
cover. Screw each cover in tightly until it will
not turn further.
• Two covers are required to be locked on the
CENELEC, IECEx, and TIIS Flameproof type
transmitters. An Allen head bolts (shrouding
bolts) are provided under edge of the each
cover for locking. When a shrouding bolts are
driven counterclockwise by an Allen wrench, it
is coming out and locks up a cover. (See page
9-3) After locking, the covers should be
confirmed not to be opened.
• Tighten the zero-adjustment cover mounting
screw to fix the cover in position.
7.4 Shutting Down Operation
Shut down the transmitter operation as follows.
1) Turn off the power.
2) Close the stop valves on the up and downstream
sides.
NOTE
Whenever shutting down the transmitter for a
long period, remove any process fluid from the
transmitter pressure-detector section.
7.5 Transmitter Measurement
Range (Determining Differen-
tial Pressure Range)
The following describes the procedure for calculating
the differential pressure range and the calculation
example in low flow measurement.
Conversion factor in pressure unit:
1 Pa=1.01972
ϫ10 -1 mmH
2
O
1 mmH
2
O=9.80665 Pa
1 atm=1.01325
ϫ10
2 kPa
7.5.1 Determining the Differential Pres-
sure Range
Use the following procedures to determine a differential
pressure range according to the fluid conditions being
measured.
(a) Calculate a water or air equivalent flow from the
flow of the fluid being measured (100% flow).
᭿ Equivalent Water Flow Calculation
Q
w
= 0.03162 . Qf .
␳f
(1)
Where, Qw: Water equivalent volumetric flow (m 3 /h) at
4 °C, 1 atm
Qf: Volumetric liquid flow (m 3 /h) at operating
conditions (t °C, p kPa)
␳f: Specific liquid density (kg/m 3 ) at operating
conditions (t °C, p kPa)