4200 Electronic Position Transmitters
The instrument can sense the position of rotary or
sliding‐stem valves, vents, dampers or other devices.
When the instrument is mounted, a potentiometer
shaft is mechanically connected to the device to sense
mechanical motion. For a standard instrument, a
single potentiometer is provided for position input or
an optional dual element potentiometer is available to
allow independent electrical operation of the
transmitter and alarm circuits.
The instrument has standard, or long‐stroke (see
figure 3), capabilities for sliding‐stem actuator
applications. For long‐stroke applications, a multi‐turn
potentiometer attached to a travel transducer
assembly is used to sense linear motion of the actuator
stem or other devices. The instrument with standard
capabilities can also be used on quarter‐turn actuators.
For instruments equipped with electronic travel limit
alarms, individual electronic high and low alarm
circuits drive separate high and low alarm SPDT relays.
The user adjusts the trip point and deadband of the
high and low alarms to the desired travel limits. When
the sense potentiometer voltage is higher than the
high trip point, the electronic high alarm circuit
de‐energizes the high alarm relay. When the sense
potentiometer voltage is lower than the low trip point,
the low alarm circuit de‐energizes the low alarm relay.
The low trip point may be offset from the high trip
point by as little as 5% of the remaining span. In the
event of a power loss to the alarm circuits, both alarms
are tripped (both relays are de‐energized). This
indicates a system failure because the actuator cannot
be physically at both travel limits simultaneously. The
relay contacts are isolated from the transmitter and
FISHER 4200 TRANSMITTER
FISHER 4200 TRANSMITTER ON A CONTROL VALVE