Emerson Rosemount 1152 Alphaline, Reference Manual

Page: 28 / 68

Reference Manual
00809-0100-4235, Rev BA
April 2007
Rosemount 1152
3-8
1. Adjust the zero to eliminate any existing zero elevation or
suppression. With 0 inH
2
O pressure applied to the transmitter, turn
the zero adjustment until the 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 inH
2
O pressure input, equals 8
mA.
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-span output and fine tune the span and zero adjustment, if
required. Remember that zero adjustments do not affect span, but
span adjustments do affect zero. Adjusting the span screw affects 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 reads 19.900 mA at 50 inH
2
O, turn the
span potentiometer until the output (at 50 inH
2
O) reads 20.025 mA.
19.900 + (20.000 – 19.900)
⫻
1.25 =
19.900 + 0.125 = 20.025.
Since the span adjustment affects zero 1 /
5
as much as the span, the
0.125 mA increase in span causes a 0.025 mA increase in zero.
Therefore, turn the zero adjustment (at 50 inH
2
O) until the output
reads 20.000 mA. The unit should now be calibrated for 0 to 50
inH
2
O.
5. Zero elevation/suppression: Elevate the zero. Turn the zero screw
until the output reads 4 mA with –75 inH
2
O applied to the high side of
the transmitter (applying 75 inH
2
O to the low side of the transmitter
will give the same result). The output may stop changing before the
desired 4 mA reading is obtained. If this occurs, turn power to the unit
off and unplug the amplifier board (refer to Electrical Housing
Disassembly on page 5-4 and Figure 5-2 on page 5-6 to locate the
amplifier board).
To elevate or suppress zero a large amount, follow either procedure A
or B, depending on whether the amplifier board has a switch (see
Figure 3-4 on page 3-6) or three turrets (see Figure 3-5 on page 3-6).
A. Amplifier Board with Switch
Method:
Locate the three-position slide switch on the component side of the
amplifier board (see Figure 3-4). Move the switch position to “elevate
zero,” plug the amplifier board back in, and complete the zero
adjustment. To suppress zero, follow the same procedures except
move the switch position to “suppress zero” (see Figure 3-4).
4mA
⫻
Existing Span
Desired Span
------------------------------------
⎝ ⎠
⎛ ⎞
4mA
⫻
100 inH
2
O
50 inH
2
O
-----------------------------
⎝ ⎠
⎜ ⎟
⎛ ⎞
8mA = =