REMOTE CONTROL POINT
A pressure change from 3 to 13 psi (21 to 90 kPa) in the
remote CPA port changes the control point proportion-
ately by 20 percent of the sensor span.
The
is raised by turning the Setpoint Knob
(Fig. 7) counterclockwise. This increases the force from
the setpoint spring on the lever assembly so that a greater
force from the sensor chamber is required to cause an
increase in branchline pressure.
The setpoint screw has a vernier for fine adjustment.
It has 10 marked divisions, each equaling l/2 percent of
the sensor span (1 degree F per division for a 200-degree
sensor span, or 20 turns for the whole span).
ADJUSTMENT
SCREW WITH
MARKED
KNOB
CONTROLLER WITHOUT CPA
BAND INDICATOR
CONTROLLER WITH CPA
2 0 8 8 7
Fig. 7. RP908 Adjustment Locations.
CALIBRATION
GENERAL
Always calibrate with 18 psi (124 kPa) main air pres-
sure. On CPA models, set CPA to 8 psi (5.5 kPa). A 0 to
30-psi gage must be installed in the branchline port
during calibration and a temperature, humidity, or pres-
sure gage matching the sensor should be installed in Port
1 (and Port 2 if RP908B is used). If the reset signal on an
RP908B is produced by the output of a room thermostat
or pressure control, a 30-psi gage must be installed in
Port 2. Otherwise, the scale range on the
gage
should
match the range of the sensor for Ports 1 and 2.
There are two methods of calibrating the RP908A
when 18 psi (124 kPa) main air is supplied to the Control-
ler and the internal restriction is not blocked.
CALIBRATION USING AN ADJUSTABLE
RESTRICTION
1,
2.
3.
4.
5.
6.
Install the proper scaleplate on the Controller if not
already installed.
Disconnect the Port 1 sensor and connect an adjust-
able restriction to Port 1.
Choose a setpoint and adjust the restriction until the
gage in Port 1 shows this setpoint.
Turn the setpoint knob until the branchline pressure
reads 8 psi (55 kPa). This is standard calibration. On
some applications, the calibration branchline pressure
may be set at a different point that relates to the spring
range of the device being operated.
Move the scaleplate until the setpoint indicator agrees
with the chosen setpoint, and tighten.
Disconnect the adjustable restriction and reconnect
the sensor.
CALIBRATION WITH GAGES
1. Install 30-psi gages in Ports 1 and B. Port I gage must
match Port B.
Install proper scaleplate on the Controller if not
already done.
Turn the setpoint knob until branchline pressure is 8
psi (55 kPa) or other selected calibration pressure (see
Step 4 of CALIBRATION USING AN ADJUST-
ABLE RESTRICTION).
Move the scaleplate until the setpoint indicator is at
the reading shown on the Port 1 gage and tighten.
Adjust the setpoint to the desired control setting.
The only method of calibrating the RP908B is to use
an adjustable restriction. If the settings are known, pro-
ceed to Step 1 of
CALIBRATION PROCE-
DURE. If the settings ‘must be calculated, read the
following and calculate as shown. Authority Calculator
No. 813 may be used to simplify these calculations.
Although these examples are shown for a hot water reset
system, the formulae also apply to other systems-
75-553 I 4
Содержание RP908A 1005
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