Siemens MS Series, Instruction Manual

Page: 83 / 130

SITRANS P, MS series
83
C79000-B5674-C40-04
On-site Operation and Display
3.1.2 Setting/Adjusting Start of Scale/Full Scale
The start of scale and full scale can be set or adjusted using the pushbuttons. A rising
or falling characteristic can be implemented in this way.
3.1.2.1 Relationships
A desired start of scale and/or a desired full scale are assigned to the standard cur-
rent values (4 mA/20 mA) when setting. Condition: Two reference pressures (p
r1
, p
r2
)
provided by the process or generated by a pressure transmitter. The measuring span
specified on the measuring point plate no longer matches the adjustment after set-
ting.
A turn-down up to 1:30 can be achieved.
The relationship between the measured pressure and the generated output current
is linear. The output current can be calculated using the following equation (Figure 8,
p. 83).
NOTE
The measuring span is not altered by setting the start of scale. The start of scale
remains unchanged when the start of scale is set.
I = output current in mA
P = applied pressure
ME = full scale
MA = start of scale
ME - MA = MS (measuring span)
Figure 8 Formula for calculating the current
NOTE
If the transmitter is operated locally, write accesses through HART® are denied
during this time. Data, e.g. measured values, can be read at any time.
I = * 16 mA + 4 mA
P - MA
ME - MA