Siemens SITRANS P300 Operating Instructions Manual page 53

Note
If the preset measuring limits are exceeded or fallen below by more than 20% during setting,
the setting function is not carried out and the old value is retained.
With a marked elevation of the zero point, the limit point must therefore previously be
reduced such that it still lies within the permitted range after elevation of the zero point. This
setting function is only possible with the "Pressure" measurement type.
Adjusting with reference pressure
Requirement:
The reference pressure, the adjusted zero point and adjusted limit point are known.
With adjusting, a zero point or limit point can be allocated to a desired current value with the
aid of a reference pressure. This function is particularly suitable when the required pressures
for zero point and limit point are not available After adjustment, the span specified on the
nameplate may no longer correspond with the setting.
Using the formulae below, the current to be set for the desired zero point and limit point can
be calculated.
To calculate the output currents when setting the zero point or limit point, the reference
pressure must be selected so that a value between 4 and 20 mA results for the current.
Figure 6-7
I
I
MA
I
ME
p
p
ref
SITRANS P300 with HART communication
Operating Instructions, 06/2005, A5E00359579-02
Current calculation formula for setting with reference pressure
Output current
Current to be adjusted with MA
Current to be adjusted with ME
Pressure
Existing reference pressure
MA Old zero point
actual
ME Old limit point
target actual
MA New zero point
target target
ME New limit point
target
Operation
6.5 Local operation
6-15