Emerson Rosemount 1154DH, Reference Manual

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Reference Manual
00809-0100-4631, Rev BA
April 2007
3-3
Rosemount 1154 Series H
Figure 3-2. Zero and Span
Adjustment Screws.
Example (for Range Code 4)
Initial transmitter calibration: 25 to 125 inH
2
O (100 inH
2
O span with zero
suppressed 25 inH
2
O).
Desired transmitter calibration: –75 to –25 inH
2
O (50 inH
2
O span with zero
elevated 75 inH
2
O).
1. Adjust the zero to eliminate any existing zero elevation or
suppression. With 0 inH
2
O pressure applied to the transmitter, turn
zero adjustment until output reads 4 mA. The unit is now calibrated
for 0 to 100 inH
2
O.
2. Adjust the span to the desired new span. To reduce the span, turn the
span screw until the output, with 0 in H
2
O pressure input, equals:
3. Adjust the zero screw to bring the output, with 0 inH
2
O input, back to
4 mA. The transmitter calibration should now be very close to 0 to 50
inH
2
O.
4. Check full-scale output and fine tune the span and zero adjustment if
required. Remember zero adjustments do not affect span, but span
adjustments do affect zero predictably. Adjusting the span screw will
affect the zero 1/5 as much as it affects the span. To compensate for
this effect, simply overadjust by 25 percent. For example, if after
completing Step 3, the transmitter output read 19.900 mA at 50
inH
2
O, turn the span potentiometer until the output (at 50 inH
2
O)
reads 20.025 mA.
Span
Screw
Zero
Screw
4mA
Existing Span
Desired Span
---------------------------------------
⎝ ⎠
⎛ ⎞
4mA
100 inH
2
O
50 inH
2
O
------------------------------
⎝ ⎠
⎛ ⎞
8mA = =
19.900 + (20.000 – 19.900) 1.25 = 19.900 + 0.125 = 20.025
1154-0314A