Yokogawa EJX115A - Manual (Page 38)

<6. Operation>
36
IM 01C25A01-01E
6.2 Zero Point Adjustment
After completing preparations for operating the
transmitter, adjust the zero point.
Zero point adjustment can be done by turning the
transmitter’s zero-adjustment screw or by using the
communicator. This section describes the procedure
for the zero-adjustment screw. For the communicator
procedure, please refer to manuals in the attached
CD-ROM.
IMPORTANT
Do not turn off the power to the transmitter
immediately after performing a zero point adjustment.
Powering off within 30 seconds of performing this
procedure will return the zero point to its previous
setting.
6.2.1 Adjusting Zero Point for Differential
Pressure Transmitters
Before adjusting zero point, make sure that the equalizing
valve is open.
Zero-adjustment screw cover
F0603.ai
Figure 6.2 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 6.2.2(2).
6.2.2 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.