Honeywell AUTOMATIC CONTROL SI Edition User Manual

PNEUMATIC CONTROL FUNDAMENTALS
ENGINEERING MANUAL OF AUTOMATIC CONTROL
79
HIGH-PRESSURE SELECTOR RELAY
The high-pressure selector relay is a three-port relay that
transmits the higher of two input signals to the output branch.
The high sensitivity of the relay allows it to be used in sensor
lines with an accuracy of 1 to 1.5 degrees C.
The application shown in Figure 39 uses pressures from two
zones and a high-pressure selector relay to determine control.
A separate thermostat controls each zone damper. The
thermostat that calls for the most cooling (highest branchline
pressure) controls the cooling valve through the high-pressure
selector relay.
Fig. 39. Typical Application for
High-Pressure Selector Relay.
LOW-PRESSURE SELECTOR RELAY
The low-pressure selector relay is a three-port relay that
selects the lower of two input pressure signals and acts as a
repeater for the lower of the two inputs. The relay requires an
external restrictor on the input to the branch port. Figure 40
shows a low-pressure selector relay controlling the heating coil
valve from the thermostat that calls for the most heat.
LOAD ANALYZER RELAY
The load analyzer relay is a bleed-type, diaphragm-logic
pressure selector. The relay selects the highest and lowest branch
pressure from multiple inputs to operate final control elements
(Fig. 41). The relay contains multiple diaphragms and control
nozzles. Each input pressure connects to two diaphragms.
Fig. 41. Load Analyzer Relay in
Multizone Air Unit Application.
In Figure 41, the load analyzer relay selects the lowest
pressure signal from the thermostat in the coldest zone and
transmits that signal to a normally open heating valve. The relay
transmits the highest pressure signal from the thermostat in the
warmest zone to a normally closed cooling valve.
CAPACITY RELAY
The capacity relay is a direct-acting relay that isolates an
input and repeats the input pressure with a higher capacity
output. Figure 42 shows a capacity relay enabling a single bleed-
type thermostat to operate multiple damper actuators quickly
by increasing the output capacity of the thermostat.
Fig. 40. Typical Application for
Low-Pressure Selector Relay.
N.C. ZONE
DAMPER
15-50 kPa
DAMPER
ACTUATOR
HIGH-PRESSURE
SELECTOR RELAY
P
1
P
2
B
DA ZONE
THERMOSTAT
N.C. ZONE
DAMPER
15-50 kPa
DAMPER
ACTUATOR
55-85 kPa
COOLING COIL
VALVE
M
DA ZONE
THERMOSTAT
MB
M15147
M
MB
N.O. ZONE
DAMPER
55-85 kPa
DAMPER
ACTUATOR
LOW-PRESSURE
SELECTOR RELAY
P
1
P
2
B
N.O. ZONE
DAMPER
55-85 kPa DAMPER
ACTUATOR
RESTRICTOR
DA ZONE
THERMOSTAT
MB
15-50 kPa N.O.
HEATING COILVALVE
M
DA ZONE
THERMOSTAT
MB
M15148
EXH
M
LOWEST
M
HIGHEST
12 3
N
LOAD ANALYZER RELAY
DA ZONE THERMOSTATS
TO
ZONE
DAMPERS
M15149
MB
M
MB
M
MB
M
M
M
MB
55-85 kPa
N.C. COOLING
VALVE
15-50 kPa
N.O. HEATING
VALVE

Honeywell AUTOMATIC CONTROL SI Edition Specifications

General

Brand	Honeywell
Model	AUTOMATIC CONTROL SI Edition
Category	Control Systems
Language	English