Emerson 1154, 00809-0100-4514 manual Zero and Span Adjustment Screws

Reference Manual

00809-0100-4514, Rev BA January 2008

Rosemount 1154

Figure 3-2. Zero and Span Adjustment Screws.

Zero

Span

Example (for Range Code 4)

Initial transmitter calibration: 25 to 125 inH2O

(100 inH2O span with zero suppressed 25 inH2O)

Desired transmitter calibration: –75 to –25 inH2O (50 inH2O span with zero elevated 75 inH2O)

1.Adjust the zero to eliminate any existing zero elevation or suppression. With 0 inH2O pressure applied to the transmitter, turn the zero adjustment until the output reads 4 mA. The unit is now calibrated for 0 to 100 inH2O.

2.Adjust the span to the desired new span. To reduce the span, turn the span screw until the output, with 0 inH2O pressure input, equals:

4 mA ×	Existing Span	= 4 mA ×	100 inH2O	= 8 mA
	-----------------------------------Desired Span-		-----------------------------50 inH2O

3.Adjust the zero screw to bring the output, with 0 inH2O input, back to 4 mA. The transmitter calibration should now be very close to 0 to 50 inH2O.

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 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 inH2O, turn the span potentiometer until the output (at 50 inH2O) 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 inH2O) until the output reads 20.000 mA. The unit should now be calibrated for 0 to 50 inH2O.

5.Zero Elevation/Suppression. Elevate zero. Turn the screw until the

output reads 4 mA with –75 inH2O applied to the high side of the transmitter (applying 75 inH2O 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 off power to the unit and unplug the amplifier board (refer to “Electrical Housing Disassembly” on page 5-6and Table 5-1 on page 5-5). To elevate or suppress zero a large amount, use the following procedure:

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