Yokogawa EJX440A - Manual (Page 27)

<3. Operation>
3-17
IM 01C25T01-01E
NOTE
Test output continues for approximately 10
minutes, then is released automatically. Even if
the HART communicator power supply is turned
off or the communication cable is disconnected,
test output will continue for approximately 10
minutes.
3.5.7 Sensor Trim
Each DPharp EJX series transmitter is factory
characterized. Factory characterization is the
process of comparing a known pressure input with
the output of each transmitter sensor module over
the entire pressure and temperature operating
range. During the characterization process, this
comparison information is stored in the transmitter
EEPROM. In operation, the transmitter uses this
factory-stored curve to produce a process variable
output (PV), in engineering units, dependent on the
pressure input.
The sensor trim procedure allows you to adjust
for local conditions, changing how the transmitter
calculates process variables. There are two ways
to trim the sensor: a zero trim and a full sensor trim.
A zero trim is a one-point adjustment typically used
to compensate for mounting position effects or
zero shifts caused by static pressure. A full sensor
trim is a two-point process, in which two accurate
end-point pressures are applied (equal to or greater
than the range values), and all output is linearized
between them.
(1) Zero Trim
a. Zeroing—Pres Zero trim
Pres Zero trim carries out the zero adjustment
and automatically sets the applied “0” input
values to the output value of “0,” keeping the
span constant. Use this setting when the LRV is
known to be 0 mmH
2
O.
1
1. Device setup
2. Diag/Service
3. Calibration
3. Pres Sensor trim
1. Pres Zero trim
EJX:YOKOGAWA
WARN-LOOP should be
removed from
automatic control
ABORT OK
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Press OK (F4).
(OK)
2
EJX:YOKOGAWA
WARN-This will affect
sensor calibration
ABORT OK
Press OK (F4).
(OK)
3
EJX:YOKOGAWA
Apply 0 input to
sensor
ABORT OK
A pressure of 0 mmH
2
O is applied.
Press OK (F4) after the pressure
has become stable.
(OK)
b. Level Adjustment—Auto, lower Pt
This zero adjustment calibrates the transmitter
output corresponding to the actual tank level. To
perform this adjustment, first use a glass gauge
or the like to determine the actual tank level,
then enter the correct data as shown below.
2500 mmH
2
O
0 mmH
2
O
Actual level
1350 mmH
2
O
DPharp span: 0 to 2500 mmH
2
O
Actual level: 1350 mmH
2
O
Transmitter output: 1383 mmH
2
O
DPharp
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