Data Sheet

2500-249 Controllers and Transmitters
D200037X012
Product Bulletin
34.2:2500
July 2012
10
Figure 5. Schematic of Direct‐Acting Fisher 2500‐249 Proportional Controller (or Transmitter) Shown with
Right‐Hand Mounting
CD2114‐E
B2296
OUTER
BOURDON
TUBE
CHANNEL
INNER BOURDON
TUBE CHANNEL
SETPOINT OR
ZERO ADJUSTMENT
FLAPPER
TORQUE TUBE SHAFT
EXHAUST
PROPORTIONAL VALVE
TO OTHER
PNEUMATIC INSTRUMENT
IF TRANSMITTER
CONSTRUCTION OR
APPLICATION
SMALL
DIAPHRAGM
SUPPLY END OF
RELAY VALVE
EXHAUST END
OF RELAY VALVE
NOZZLE
FIXED
ORIFICE
EXHAUST
SUPPLY
PRESSURE
LARGE
DIAPHRAGM
SUPPLY PRESSURE
NOZZLE PRESSURE
OUTPUT PRESSURE
PROPORTIONAL PRESSURE
Supply Pressure
Overpressure Protection
Applying excessive pressure to any portion of a
controller, transmitter or connected equipment may
cause leakage, part damage, or personal injury due to
bursting of pressure‐containing parts. Although the
standard 67CFR supply regulator for 2500 instruments
has internal relief to provide very limited overpressure
protection, complete overpressure protection
between the supply regulator outlet and the
instrument case is needed if a malfunctioning supply
regulator can deliver a supply pressure that exceeds
3.4 bar (50 psig).
Principle of Operation
All 2500 controllers and transmitters use the same
basic pressure‐balanced relay with a yoked
double‐diaphragm assembly. Supply pressure either
passes through the fixed orifice and bleeds out the
nozzle (figure 5 or 6) or directly enters the Bourdon
tube valve (figure 7). Nozzle pressure registers on the
large relay diaphragm, and output pressure on the
small relay diaphragm.
The following descriptions show how the various
controller and transmitter constructions work in
conjunction with displacer action.