Yokogawa EJX930A - Manual (Page 43)

<6. Explanation of Basic Items>
6-4
IM 01C25R03-01E
F0604.ai
0 0
Calculated Value Calculated Value Span
adjustmen
point
After zero
adjustment
After zero adjustment
After zero/span
adjustment
Input pressure Input pressure
Before zero
adjustment
CAUTION
Span adjustment is a function for adjusting
the gradient with respect to the point of zero
adjustment. If that point is not zero, the gradient
of input and output values cannot be accurately
adjusted. Perform span adjustment after zero
adjustment is completed.
Diagnosis of adjustment results:
When the amount of zero adjustment or span
adjustment exceeds any of the following adjustment
limits, “AL50: Adjustment range error for differential
pressure” is displayed.
The conditions for zero/span adjustment are as
follows:
<1> The point of zero adjustment is within
±10% of the capsule range.
<2> The amount of zero adjustment is within
±10% of the capsule range.
<3> The point of span adjustment is within the
capsule range.
<4> The input and output gradients after span
adjustment are within ±10% of the gradient at
factory setting.
6.3.4 Functions Relating to Static
Pressure
Reference to static pressure value:
In SECONDARY_VALUE and TERTIARY_VALUE,
it is possible to refer to the H-side static pressure
value and the L-side static pressure value,
respectively. The update period of these values
is 200 mseconds. The pressure unit is selected
by XD_SCALE.unit in the AI block, in which
SECONDARY_VALUE and TERTIARY_VALUE
are 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 specifics, refer to Table 8.9.
Setting of signal damping for static pressure:
SP_VALUE_FTIME is parameter that set signal
damping for static pressure signals. The unit of the
signal damping is second.
Determination of the range limit of static
pressure signal:
When the static pressure signal exceeds the
maximum working pressure (MWP) of the capsule,
set the status of PRIMARY_VALUE to Uncertain-
Subnormal. Also, set the status of SECONDARY_
VALUE and TERTIARY_VALUE to Uncertain-
Sensor Conversion not Accurate. The status under
normal conditions is Good-Non Specific.
Adjustment of static pressure signal:
The zero/span adjustment function can be used for
static signals, as in the case of differential pressure
signals. However, the zero-point adjustment by the
external screw function is not supported for static
pressure signal.
Automatic adjustment
The value of the static pressure exerted on the
point where adjustment is to be made is assigned
to parameters (CAL_SP_POINT_LO, CAL_SP_
POINT_HI). After this assignment is set, the amount
of adjustment is calculated by the transmitter and
automatically updated. The procedure for adjusting
the static pressure signal is the same as that of
differential pressure signal.
Manual adjustment
From the exerted pressure and the output of the
transmitter, calculate the amount of zero/span
adjustment manually and assign the calculated
value to parameters (CAL_SP_DEVIATION_LO,
CAL_SP_DEVIATION_HI).
Selection of static pressure signal type:
EJX910 multivariable transmitter measure the
absolute static pressure. Based on the assumption
that atmospheric pressure is constant, these
transmitters can output signal equivalent to gauge
pressure calculated by deducting the atmospheric
pressure (fixed value) from the measured absolute
pressure. The type of static pressure signal output
to SECONDARY_VALUE and TERTIARY_VALUE
is selected in SP_VALUE_TYPE. SP_VALUE_
TYPE allows selection of gauge pressure or
absolute pressure. When selecting gauge pressure,
set the value of the atmospheric pressure (fixed
value) to ATM_PRESS. The default value of
ATM_PRESS is equal to the value of standard
atmospheric pressure (101.325 kPa).