P i p i n g
The field sample line connectors, two
1/4" - 18 NPT female fittings, labeled
H (high)
and
L (low)
, are located on
the side of the enclosure as shown in
Figure 1.
Positive Pressure only:
Connect sample line to
H
;
L
remains open to the atmosphere.
Negative Pressure only:
Connect sample line to
L
:
H
remains open to the atmosphere.
Two Negative Samples:
Connect higher negative sample to
L
:
Connect lower negative sample to
H
.
Two Positive Samples:
Connect higher positive sample to
H
:
Connect lower positive sample to
L
.
O n e N e g a t i v e a n d O n e P o s i t i v e
Sample:
Connect positive sample line to
H
:
Connect negative sample line to
L
.
For each right angle bend, add four
feet to the computed line length in order
to determine correct pipe or tubing size.
If either sample line connector is
vented to the atmosphere, attach an el-
bow to it so that the open end of the con-
nector points downward. This will help
protect the switch from contamination.
Electrical Connections
Five numbered terminals are provided
for field wiring. Terminals are pressure
clamp screw type.
Sequence of Operation
Before pressure and power are applied
to the AFS-952, the SPDT switch con-
tacts are in the normally closed posi-
tion as shown in
Figure 3
(“shelf” con-
dition), and relay contacts 3 and 5 are
closed (“alarm mode”).
When the sample lines are con-
nected as shown in
Figure 1
, and
power is applied to terminals 1 and 2,
the following sequence occurs.
Initially the red lamp is on, indi-
cating that differential pressure is less
than set point. The SPDT switch con-
tacts remain in the NC position for as
long as differential pressure remains
less than set point; the TD1 time delay
is not energized and the K1 load relay
circuit remains in alarm mode. When
differential pressure reaches set point,
the SPDT switch contacts change to
NO immediately so that the red lamp
goes out and the TD1 time delay is en-
ergized. If the TD1 time delay remains
energized for 8 ± 3 seconds continu-
ously, the TD1 contacts close, ener-
gizing the K-1 coil and opening K-1
load contacts 3 and 5. The circuit is
now in normal operating mode.
Whenever differential pressure
drops below the set point, the SPDT
switch contacts change to NC imme-
diately, turning the red lamp on, and
de-energizing the TD1 time delay.
The
K-1 load contacts for terminals 3
and 5 remain open unless differen-
tial pressure remains less than set
point for 8 seconds continuously
.
After this 8-second period, K-1 load
relay contacts 3 and 5 close while K1
contacts 3 and 4 open: the circuit is
now in
alarm mode
.
When the differential pressure be-
comes greater than set point, the SPDT
switch contacts change to NO imme-
diately, turning the red lamp off, and
energizing the TD1 time delay. The dif-
ferential pressure must remain greater
than set point for 8 seconds continu-
ously before the K-1 load relay con-
tacts open contacts 3 and 5.
Field Adjustments
Field adjustments to the operating set
point are made by removing the protec-
tive plug button on the side of the con-
trol enclosure and inserting a standard
blade-type screwdriver, at least 3 inches
long*.
The adjustment range is
0.05 ± .02"
w.c. to 12.0" w.c.
To adjust the set point,
Model AFS-952
Air Pressure Sensing Switch
Mounting Position:
Mount with the
diaphragm in any vertical plane.
Set Point Range:
0.05 ± 0.02" w.c. to
12.0"w.c. (1.3 to 305 mm wc; 0 to 0.43
psi).
Field Adjustable
“Operate Range”:
0.07"w.c. to 12.0" w.c.
Field Adjustable
“Release Range”:
0.04"w.c. to 11.2" w.c.
Approximate Switching Differential:
Progressive, increasing from 0.02± 0.01"w.c.
at minimum set point to approximately 0.8"
w.c. at maximum set point. (0.5 ± .25 mm to
approximately 20.3 mm).
Operating Temperature Range:
0F to 130F
(-18 to 54.4C).
Measured Media:
Air or combustion by-
products that will not degrade silicone.
Maximum Pressure:
½ psi (0.03 bar).
Life:
100,000 cycles minimum at 1/2 psi
maximum pressure each cycle and at
maximum rated electrical load.
Electrical Rating–Relay Switching
Capacity:
720 va at 120 vAC at 50/60 Hz.
10 amps at 120 vAC,
5 amps at 240 vAC resistive load.
Power consumption: 4.5 watts at 120 vAC.
Contact Arrangement:
SPDT NC (single
pole, double-throw snap action switch;
contacts are in normally closed position
before pressure is applied to the diaphragm.)
Electrical Connections:
5 numbered
terminals, pressure clamp screw type.
Conduit Opening:
7/8" diameter opening
accepts 1/2" conduit.
Sample Line Connectors:
Two ¼"—18
NPT female fittings.
Approval:
FM approved.
Shipping Weight:
AFS - 952 (std. enclosure):
5 lbs.
AFS - 952 - 1 NEMA 4 enclosure:
8 lbs.
AFS - 952 - 2 NEMA 7/9 enclosure:
18 lbs.
*Standard enclosure only.
L
H
H
L
H: L:
HIGH POSITIVE LOW POSITIVE
POSITIVE NEGATIVE
LOW NEGATIVE HIGH NEGATIVE
Figure 1
1
2
3
4
5
G
K1 Load
Relay Contacts
120 V
Common
(Load)
Control
with Delay
Alarm
with Delay
Ground
1
2
9
1 0
1
2
3
4
Typical Draft Control System Connections
Series 7700
Draft Control Terminals:
:
AFS-952 Terminals:
Series 9500
Draft Regulator Terminals
wire in series with
the safety limits.
turn the adjusting screw counterclockwise
until motion has stopped. Next, turn the
adjusting screw
4 complete turns
in a
clockwise direction to engage the spring.
For the
next 10 turns,
each full turn
represents approximately 1.2" w.c.
At
higher operating pressures, there is a
slight increase in the switching differ-
ential.
Please note:
To properly calibrate
an air pressure sensing switch, a digital
manometer or other measuring device
should be used to confirm the actual set
point.
Figure 2: Electrical Connections
