IM 01C25B01-01E
7-3
7. OPERATION
7.2.1 Adjusting Zero Point for Differential
Pressure Transmitters
Before adjusting zero point, make sure that the equaliz-
ing valve is open.
F0704.EPS
Zero-adjustment
screw cover
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=
x 100=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 communi-
cator 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.
IMPORTANT
• Remove the communicator from the terminal
box, and confirm that none of the terminal
screws are loose.
• Close the terminal box cover and the amplifier
cover. Screw each cover in tightly until it will
not turn further.
• There are two covers that must be locked on
the ATEX Flameproof type transmitters. An
Allen head bolt (shrouding bolt) under the edge
of each cover is used to lock the cover. When
the shrouding bolt is driven counterclockwise
with an Allen wrench, the bolt rotates upward
and locks the cover. (See section 8.4.) After
locking the covers, confirm that they are secure
and cannot be opened by hand.
Tighten the zero-adjustment cover mounting
screw to secure the cover.
