<6. Operation>
6-2
IM 01C25W05-01EN
6.2 Zero Point Adjustment
IMPORTANT
Do not turn off the power to the transmitter
immediately after a zero adjustment.
Powering off within 30 seconds after a zero
adjustment will return the adjustment back to the
previous settings.
Adjust the zero point after operating preparation is
completed. The zero point adjustment can be made
in the following way.
Adjustment
Method
Description
Using the
HART
configuration
tool
a) Set the present input to 0%.
Adjust for 0% output at input level of 0%.
b) Adjust output to the reference value
obtained using other means.
If the input level cannot easily be made
0% (because of tank level, etc.), adjust
output to the reference value obtained
using other means, such as a sight
glass.
Using the
external zero-
adjustment
screw
c) Adjust zero point using the zero-
adjustment screw on the transmitter
Zero point adjustment is possible
without using the HART configuration
tool. Accurately adjust the output current
to 4 mA or other target output value
using an ammeter that accurately reads
output currents.
a) Set the present input to 0% (4 mA).
In this case, follow the procedure below.
This method can be used when the pressure
corresponding to the low limit of the measuring
range is zero.
• Recalling and setting the zero point adjustment
parameter (DP Zero trim)
Recall
parameters
[Root menu] (refer to section 7.2.1) →
Maintenance → DP trim →
DP Zero trim
(method)
Confirm the value after it has stabilized.
On the DP Zero trim method screen, check that the
applied zero pressure has stabilized and confirm
the value.
b) Adjust output to the reference value
obtained using other means.
In tank level measurement, if the actual level cannot
be brought to zero for zero adjustment, then the
output can be adjusted to correspond to the actual
level obtained using another measuring instrument
such as a sight glass.
An example of a differential pressure transmitter
whose span is 0 to 25.00 kPa, current level is 13.50
kPa, and the current output is 13.83 kPa is shown
below.
• Recalling and setting the zero point adjustment
parameter (DP trim)
Recall
parameters
[Root menu] → Maintenance → DP trim
→ DP trim (method)
Auto, Lower
Pt
Set the target value.
On the DP trim method screen, select Auto, Lower
Pt, and enter the actual level 13.50 kPa on the
display screen. This will change the current output
from 13.83 kPa to 13.50 kPa.
25.00 kPa
0.00 kPa
Present level
13.50 kPa
Span: 0 to 25.00 kPa
Present level: 13.50 kPa
Present output: 13.83 kPa
F0603.ai
Figure 6.3
Tank Level Measurement
c) Using the external zero-adjustment screw
The zero-adjustment screw is only available on the
high pressure side transmitter (master). Parameter
Ext SW can be used to enable or disable the zero
point adjustment using the external zero-adjustment
screw on the transmitter.
To use the external zero-adjustment screw, select
Enabled (the factory default setting is Enabled).
For the setting procedure, see subsection 7.2.3.11.
While viewing the output value, turn the zero-
adjustment screw on the outside of the transmitter
case using a slotted screwdriver so that the output
value is set to zero. 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.
