4200 Series Transmitters
Instruction Manual
Form 5596
July 2005
19
High and Low Position Switch
Adjustment
Note
The “high” and “low” designations
refer to the voltage output of the
position potentiometer. See figure 7
for relationship to valve or actuator
travel.
The high position switch must be
adjusted before the low position
switch. If the deadband of either the
high or low position switches exceeds
the difference between the set points
of the high and low position switches,
both position switches may be on at
the same time.
The following procedure sets the high and low
position switches, and the deadband for each of
them. The high position switch must be adjusted
before the low position switch. Use an ohmmeter
connected between the normally closed (NC) and
common (C) connections on terminal block TB1
(high switch) or TB2 (low switch) to observe relay
switching action as directed by the procedures.
The potentiometer alignment procedures must be
performed before calibrating the position switch
circuits. For transmitter and position switch switch
conditions, refer to figure 7 while performing the
following calibration:
1. If necessary, perform the potentiometer
alignment procedure.
2. Remove power from the instrument.
3. Remove the transmitter covers.
4. To provide an indication of switch conditions,
remove power from the instrument. Disconnect the
position switch field wiring from TB1 and TB2, and
connect an ohmmeter to TB1 between the (NC) and
(C) terminals (figure 4).
Turn both the high and low deadband
potentiometers (DBH, R4, and DBL, R5) fully
counterclockwise to set the deadbands to minimum
and set the low position switch potentiometer (LOW,
R6) fully counterclockwise.
Note
The potentiometers are 25 turn
trimpots with a slip clutch. To set
these potentiometers at their
maximum counterclockwise position,
turn them 25 or more turns in the
counterclockwise direction.
Setting the High Position Switch
For Type 4210, 4220, 4212, 4222, and 4215 direct
acting transmitters, refer to figure 5 for location of
adjustments.
1. Turn the high position switch potentiometer
(HIGH, R3) fully clockwise.
2. Stroke the valve or device to the point of travel
where the high position switch is to operate (see
figure 7).
3. Apply power to the instrument.
4. Turn the high position switch potentiometer (R3)
slowly counterclockwise until the high position switch
trips, the ohmmeter changes from a high resistance
to a low resistance reading.
5. The high position switch is now set.
Setting the High Position Switch
Deadband
1. Slowly stroke the actuator or device between the
tripped and reset point of the high position switch.
Observe this by the changing readings of the
ohmmeter. Note the differences in travel between
the trip point and reset points. This is the deadband
of the switch.
2. If necessary, increase the deadband by turning
the potentiometer (DBH, R4), clockwise.
3. Repeat steps 1 and 2 until the desired deadband
setting is obtained.
Setting the Low Position Switch
Note
Perform the high position switch
adjustment procedures before
adjusting the low position switch.
1. To provide an indication of switch condition,
remove power from the instrument. Connect an
ohmmeter to TB2 between the (NC) and (C)
terminals (figure 4).
2. Stroke the device to the point of travel where the
low position switch is to operate (See figure 7).
