YOKOGAWA DpharpEJX vigilantplant EJX Series - Functions Relating to Pressure;Differential Pressure

IM 01C25T02-01E
6-2
6. EXPLANATION OF BASIC ITEMS
6.3.3 Functions Relating to Pressure/
Differential Pressure
Reference to pressure/differential pressure value:
By accessing PRIMARY_VALUE, it is possible to
refer to the pressure/differential pressure value and
status. The update period of this value is 100 msec.
The pressure unit is selected by XD_SCALE.unit of
the AI block, in which PRIMARY_VALUE is selected.
The status is normally Good-Non Specific. However,
in the case of a sensor failure or out of measurement
range, it turns to Bad or Uncertain. For details, refer to
Table 8.9.
Setting of signal damping for pressure/differential
pressure:
When the pressure/differential pressure signal fluctu-
ates greatly, the fluctuation can be reduced by increas-
ing the time constant for signal damping.
PRIMARY_VALUE_FTIME is the parameter for
setting the signal damping for pressure/differential
pressure. The unit of signal damping is second.
Determination of the range limit of pressure/
differential pressure signal:
When the pressure/differential pressure signal deviates
more than 10% from the capsule measurement range
shown in PRIMARY_VALUE_RANGE, set the status
of PRIMARY_VALUE to Uncertain-Sensor Conver-
sion not Accurate.
Adjustment of pressure/differential pressure signal:
EJX Series Pressure/Differential Pressure Transmitters
have been accurately adjusted according to the specifi-
cations at factory setting. Minimal errors can occur due
to the environment where the transmitter is installed
and the mounting position. To fine-tune any errors,
three zero/span adjustment functions can be used:
automatic and manual zero/span adjustment by com-
munication terminals, and zero-point adjustment by
means of the external adjustment screw on the trans-
mitter.
Automatic adjustment
The value of the pressure exerted on the point where
the adjustment is to be made is assigned to parameters
(CAL_POINT_LO, CAL_POINT_HI). After this
assignment is set, the amount of adjustment is calcu-
lated by the transmitter and automatically updated.
Manual adjustment
From the exerted pressure and the output of the
transmitter, calculate the amount of zero/span adjust-
ment manually, and assign the calculated value to
parameters (CAL_DEVIATION_LO,
CAL_DEVIATION_HI).
Zero-point adjustment by the external screw.
With pressure being exerted on the point where the
adjustment is to be made, zero adjustment needs to be
performed. To do this, adjust the calculated value by
turning the external Zero-point adjustment screw, so
that it agrees with the actual input pressure (true
value). The output value increases when the screw is
rotated to the right. It decreases when the screw is
rotated to the left. The adjustment width is small when
the rotation speed is low and large when fast.
When performing zero-point adjustment by the external
screw, EXTERNAL_ZERO_TRIM needs to be set to
“Enable.”