Siemens SITRANS P Bedienungsanleitung PDF herunterladen (Seite 106)

On-Line Operation UMSITRPDS3-1

November 2010

6-8

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 first formula. Then calculate the current to be set at p

fsn

using the second formula.

mAmA

zofso

znref

416 +∗

−

fsn

mAmA

znfsn

znref

416 +∗

−

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.

I = output current

ref

= applied reference pressure

fso

= old full scale (ME

act

in leporello)

= old start of scale (MA

act

in leporello)

fsn

= new full scale (ME

nom

in leporello)

= new start of scale (MA

nom

in leporello)

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