Emerson Rosemount 1152 Alphaline, Reference Manual

Page: 12 / 68

Reference Manual
00809-0100-4235, Rev BA
April 2007
Rosemount 1152
2-2
Process Connections
Process tubing installation must prevent any added mechanical stress on the
transmitter under seismic disturbances. This may be done by using
stress-relief loops in the process tubing or by separately supporting the
process tubing close to the transmitter.
Process connections on the transmitter flanges are ¼–18 NPT. Use thread
sealant when making connections. Valve seats or plugs should also be sealed
with thread sealant. Torque to 200 in-lbs (22.4 N-m).
The user assumes responsibility for qualifying
1
/
4
- 18 NPT connection
interfaces.
If the drain/vent valves must be opened to bleed the process lines, torque to
7.5 ft-lb (10.2 N-m) when closing.
Proper location of the transmitter with respect to the process tubing depends
on process parameters. Consider the following in determining the best
location:
• Keep hot or corrosive process fluids from contacting the transmitter.
• Prevent sediment from depositing in the impulse tubing.
• Keep impulse tubing as short as possible.
• Ambient temperature gradients and fluctuations can result in erroneous
transmitter readings.
• For differential transmitters, balance the liquid head on both legs of the
impulse tubing.
• For liquid flow or pressure measurements, make taps to the side of the
line to avoid sediment deposits, and mount the transmitter beside or
below the taps so that gases vent into the process line (see Figure 2-3
on page 2-6).
• For gas flow or pressure measurements, make the taps on the top or
side of the line and mount the transmitter beside or above the taps so
that liquid drains into the process line (see Figure 2-3 on page 2-6).
• For steam flow or pressure measurements, make taps to the side of the
line, and mount the transmitter below the taps so the impulse tubing
stays filled with condensate (see Figure 2-3 on page 2-6).
• For steam service, fill lines with water to prevent steam from contacting
the transmitter. Condensate chambers are not necessary since the
volumetric displacement of the transmitter is negligible.
The piping between the process and the transmitter must transfer the
pressure measured at the process taps to the transmitter. Possible sources of
error in this pressure transfer are:
• Leaks
• Friction loss (particularly if purging is used)
• Trapped gas in a liquid line or trapped liquid in a gas line (head error)
• Temperature-induced density variation between legs (head error), for
differential transmitters