Rosemount 1199 - Calibration; Zero Suppression; Zero Elevation

Section
3-1
3 Calibration
APPLICATION
CONSIDERATIONS
Diaphragm seal installations frequently require transmitters to be calibrated with
suppressed or elevated zeroes. For more extensive calibration information see the
applicable transmitter manual.
Zero suppression
A suppressed zero is needed when a gage or absolute pressure transmitter is
mounted below the high side tap (the bottom process connection). When the
transmitter is mounted below the high side tap, the fill fluid in the capillary puts
pressure on the transmitter sensor causing it to give a positive pressure reading
even when the tank is empty.
Zero elevation
Conversely, an elevated zero is needed for a gage or absolute transmitter mounted
above the high side tap (the bottom process connection) or for a two seal differential
pressure application. In these cases, the transmitter reads a negative pressure
when the tank is empty, due to the head pressure effect of the capillary fill fluid.
Maximum Span
Calculation
Example 1 calculates the maximum amount of zero elevation or suppression for a
transmitter of a specific range. The results of the calculation will help in
determining the mounting location for the transmitter.
Example 1
Mounting Considerations for a Model 3051 Range 2 Transmitter/Seal System.
Maximum height of process fluid (H) = 65 inches (165 cm)
Specific gravity of the process fluid (s
p
) = 1.0 inH
2
O/inch,
(ρ
p
) = (1 000 kg/cm
3
)
Transmitter Lower Range Limit (LRL) = -250 inH
2
O (- 620 mbar)
Transmitter Upper Range Limit (URL) = 250 inH
2
O (620mbar)
Specific gravity of the (Inert) capillary fill fluid (s
f
) = 1.85 inH
2
O/inch
r
f
= (1 850 kg/m
3
)
Gravity Constant (g) for SI Units: 9,81 m/s
2
American Units URL > (h) (s
f
) + (H) (s
p
) > LRL
250 inH
2
O > (h) (1.85 inH
2
O/inch) + (65 inches) (1.0 inH
2
0/inch) > -250
185 inH
2
O > (h) (1.85 inH
2
O/inch) > -315 inH
2
O
100 inches > (h) > -170 inches
Step 4
Step 1
Step 2
Step 3