Siemens 7MF4333 User Manual page 106

On-Line Operation
Given
Set Zero
Set Full Scale
Calculate Output Current
Adjusting Zero and Full Scale from a Single Reference
Zero and full scale can be adjusted to any desired current using only one reference pressure. This is
particularly useful if the pressures necessary for zero and full scale are unavailable. Note that after the
adjustment is completed, the measuring range on the rating plate may not match the new range.
Required to be known: The reference pressure, present zero value, and present full scale value.
Calculate the current to be set at p
using the second formula.
−
p p
p = ∗
16
ref zn
I mA
zn
−
p p
fso zo
−
p p
= ∗
p
16
ref zn
I mA
fsn
−
p p
fsn zn
An example of the use of these equations is given below. The figure following the example illustrates
these steps.
1. Given: A transmitter with a measuring range of 0 to 160 psi. Change the span to 20 to 140 psi. A
reference pressure of 110 psi is available.
2. Apply the reference pressure.
3. Calculate zero (20 psi) using the first formula.
4. Press the transmitter's M pushbutton to go the mode 2. Set the output current to 13 mA.
5. Calculate full scale (140 psi) using the second formula.
6. Press the transmitter's M pushbutton to go to mode 3. Set the output current to 16 mA.
6-8
using the first formula. Then calculate the current to be set at p
zn
+
4
mA
+
4
mA
I = output current
p = applied reference pressure
ref
p = old full scale (ME
fso
p = old start of scale (MA
zo
p = new full scale (ME
fsn
p = new start of scale (MA
zn
UMSITRPDS3-1
in leporello)
act
in leporello)
act
in leporello)
nom
in leporello)
nom
November 2010
fsn