Yokogawa EJA110E - Manual (Page 36)

<7. Operation>
7-3
IM 01C25B01-01E
7.2.1 Adjusting Zero Point for Differential
Pressure Transmitters
Before adjusting zero point, make sure that the
equalizing valve is open.
Zero-adjustment
screw cover
F0705.ai
Figure 7.4 External Zero Adjustment Screw
The zero-adjustment screw is located inside the
cover.
Use a slotted screwdriver to turn the zero-
adjustment screw. Equalize the transmitter, then
turn the screw clockwise to increase the output or
counterclockwise to decrease the output. The zero
point adjustment can be made with a resolution
of 0.01% of the setting range. The degree of zero
adjustments varies with the screw turning speed;
turn the screw slowly to make a fine adjustment,
quickly to make a rough adjustment.
When using differential pressure transmitters for
level measurement and if you cannot obtain the
lower range value from the actual measurement
value of 0%, refer to subsection 7.2.2(2).
7.2.2 Adjusting Zero Point for Gauge/
Absolute Pressure Transmitters
(1) When you can obtain the Low Range Value
from the actual measured value of 0% (0
kPa, atmospheric pressure);
For pressure measurement using gauge pressure
transmitters, follow the steps below before
performing zero point adjustment.
1) Close the tap valve (main valve).
2) Loosen the fill plug so that the pressure applied
to the transmitter is only the head of the seal
liquid.
3) Adjust the zero point at this status.
4) After the adjustment, close the fill plug and then
gradually open the tap valve.
Use a slotted screwdriver to turn the zero-
adjustment screw. Turn the screw clockwise
to increase the output or counterclockwise to
decrease the output. The zero point adjustment can
be made with a resolution of 0.01% of the setting
range. Since the degree of the zero adjustment
varies with the screw turning speed, turn the screw
slowly to make a fine adjustment and quickly to
make a rough adjustment.
(2) When you cannot obtain the Low Range
Value from the actual measured value of
0%;
Adjust the transmitter output to the actual measured
value obtained by a digital manometer or a glass
gauge.
[Example]
The measuring range of 50 to 250 kPa; the actual
measured value of 130 kPa.
130–50
250–50
Actual measured value= x100=40.0%
(=10.4mA)
Turn the screw to match the output signal to the
actual measured value.
7.3 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.