Maintenance; Module Final Assembly; Removing The Module Final Assembly - Emerson Fisher 846 Instruction Manual

Instruction Manual
Form 5739
February 2002
Section 6

Maintenance6-6-

Section 6 describes the major components,
assembly, and disassembly of the Type 846 and
Model 3311 current-to-pressure transducers.
WARNING
Use only the procedures and new
parts specifically referenced in this
manual. Unauthorized procedures or
parts can affect product performance
and the output signal used to control
a process, and may render the
instrument dangerous.

Module Final Assembly

The active mechanical and electrical components of
the transducer are incorporated into a single,
field-replaceable module called the module final
assembly, as shown in figure 6-1. Electrical
connection between the terminal compartment and
module final assembly is made by electrical
feedthroughs that extend into the module
compartment. The feedthroughs enter sockets on
the electronic circuit board. The span and zero
screws extend through the terminal compartment
wall into the module compartment. Connection to the
span and zero potentiometers on the electronic
circuit board is made by VelcroR.
The module final assembly has three separate radial
ports. The upper port is for supply air, the middle
port for the output signal, and the lower ports for
exhaust. Three O-rings separate the ports. The two
lower O-rings are the same size, and the upper
O-ring is slightly smaller. Table 6-1 shows O-ring
sizes.
The module final assembly is attached to the module
cover, which allows insertion and removal, and can
be separated from the module cover for further
disassembly. A module cover O-ring provides a seal
between the module cover and module final
assembly. Table 6-1 shows the O-ring sizes. A slip
ring is located around the module feet. It allows the
module cover to turn easily when the module final
assembly is being removed from the housing.
Table 6-1. O-Ring Sizes
Description
Module O-rings
Pilot/Actuator O-rings
Circuit Board O-rings
Module Cover O-ring
Terminal Cover O-ring
Filter–Regulator O-ring
The module final assembly consists of three major
subassemblies, as shown in figure 6-1. They are the
electronic circuit board, pilot/actuator assembly, and
module subassembly.

Removing the Module Final Assembly

The module final assembly is attached to the module
cover. Removing the module cover automatically
removes the module final assembly from the
housing. When the module cover is unscrewed, the
electrical feedthroughs and span and zero
adjustments automatically disengage. The internal
air ports are also disengaged. The air supply to the
transducer should be turned off to prevent
uncontrolled air loss through the housing.
WARNING
Personal injury or property damage
could result from an uncontrolled
process. Unscrewing the module
cover removes power from the
electronics and the output signal will
be 0.0 psi. Before removing the
module cover, ensure the process is
properly controlled.
WARNING
Personal injury or property damage
could result from fire or an explosion.
In explosive atmospheres, remove
power and shut off the air supply to
the transducer before attempting to
remove the terminal compartment
cover or module cover. Failure to do
so could result in an electrical spark
or explosion.
Use the following steps to remove the module final
assembly from the housing and module cover:
1. Shut off the air supply. If applicable, remove the
cover lock and screw to allow access to the terminal
Maintenance
Qty. Size
1 043
2 042
2 006
2 016
1 005
1 238
1 238
1 114
6–1