Compensated Control System; Electric-Pneumatic Relay Control; Pneumatic-Electric Relay Control - Honeywell Pneumatic Controls Engineering Manual

Pneumatic Control Combinations
FROM
COMPRESSOR
TWO-PRESSURE
REDUCING VALVE
Fig. 66. Two-Pressure Main Supply System
with Automatic Changeover.

Compensated Control System

In a typical compensated control system (Fig. 67), a dual-input
controller increases or decreases the temperature of the supply
water as the outdoor temperature varies. In this application, the
dual-input controller resets the water temperature setpoint as a
function of the outdoor temperature according to a preset
schedule. The system then provides the scheduled water
temperature to the convectors, fan-coil units, or other heat
exchangers in the system.
M
B M S 1
VALVE
CONTROLLER
Fig. 67. Compensated Supply Water System
Using Dual-Input Controller.

Electric-Pneumatic Relay Control

Figure 68 shows one use of an E/P relay in a pneumatic control
circuit. The E/P relay connects to a fan circuit and energizes
when the fan is running and de-energizes when the fan turns
off, allowing the outdoor air damper to close automatically when
the fan turns off. The relay closes off the controller branchline,
exhausts the branchline going to the damper actuator, and
allows the damper to go to its normal (closed) position. Figure
69 shows an E/P relay application that shuts down an entire
control system.
MIXED AIR
SENSOR
X O C
M
B M S
DA CONTROLLER
Fig. 68. Simple E/P Relay Combination.
150 customer.honeywell.com
THERMOSTAT
OR TIME CLOCK
E/P RELAY
C
X
EXH
O
GAUGE
MAIN
AIR
X = NORMALLY DISCONNECTED
O = NORMALLY CONNECTED
HOT WATER SUPPLY
TEMPERATURE
SENSOR
OUTDOOR AIR
S 2
TEMPERATURE
SENSOR
FAN
VOLTAGE
E/P
RELAY
N.C. DAMPER
N.C. DAMPER
EXH
ACTUATOR
C2361
ELECTRIC
POWER
E/P RELAY
M
C2376
Fig. 69. E/P Relay Combination for System Shutdown.

Pneumatic-Electric Relay Control

A P/E relay provides the interlock when a pneumatic controller
actuates electric equipment. The relays can be set for any
desired pressure. Figure 70 shows two P/E relays sequenced
to start two fans, one at a time, as the fans are needed.
THERMOSTAT
M B
M
Fig. 70. P/E Relays Controlling Fans in Sequence.
C2356
On a rise in temperature, Relay 1 puts Fan 1 in operation as the
thermostat branchline pressure reaches 7 psi. Relay 2 starts
Fan 2 when the controller branchline pressure reaches 12 psi.
On a decrease in branchline pressure, Relay 2 stops Fan 2 at
10 psi branchline pressure, and Relay 1 stops Fan 1 at 5 psi
branchline pressure.
Figure 71 shows two spdt P/E relays starting and stopping a
two-speed fan to control condenser water temperature.
LOW SPEED
HIGH AUXILIARY
P/E RELAY 1
C N.C. N.O.
SET 7-9 PSI
Fig. 71. Two-Speed Fan Operated by P/E Relays.
70-6925
SYSTEM
INTERLOCK
VOLTAGE
THERMOSTAT
M B
X O C
EXH
WIRED TO
START FAN 1
C N.C. N.O. P/E RELAYS
SET
5-7 PSI
COOLING TOWER
FAN STARTER
CONTROL VOLTAGE
OVERLOAD
HIGH SPEED
LOW AUXILIARY
FAN STARTER
P/E RELAY 2
C N.C. N.O.
SET 12-14 PSI
CONTROLLER
N.C.
VALVE
C2358
WIRED TO
START FAN 2
C N.C. N.O.
SET
10-12 PSI
C2359
SENSOR IN
DA
CONDENSER
WATER
B M S
M
C2367