UniControl Cleveland Controls AFS-953 User manual

Bulletin AFS953.00
Model
AFS–953
DESCRIPTION &
OPERATION
The Cleveland Controls AFS-953 Dif-
ferential Pressure Sensing Switch is
designed to provide precise operation
and convenient features for industrial
and commercial air handling applica-
tions. The AFS-953 can monitor posi-
tive, negative, or differential pressure
(flow) of air and noncombustible gases,
and is commonly used to monitor com-
bustion air, furnace pressure, ventilat-
ing blower operation, inflatable struc-
ture pressure, fume hood operation, bag
house air flow, dirt accumulation in air
filters, and heat-transfer air flow. The
AFS-953 has a field–adjustable set
point range of 0.05"wc to 12.0"wc with
a 20-second pre-purge delay and an
8-second (± 3 seconds) time delay re-
lay sequence. The time delay prevents
nuisance shutdowns due to normal draft
fluctuations.
COMMON
APPLICATIONS
The most common specific application
for the AFS-953 is as a Low Draft
(Negative Pressure) Cutoff Safety
Switch for combustion draft control
systems where individual pre-purge is
needed. In general, the AFS-953 can
be applied as follows:
•Low Positive Pressure Cutoff.
(Shutdown upon insufficient pres-
sure.)
•Low Negative Pressure Cutoff.
(Shutdown upon insufficient
draft.)
•Low Differential Pressure Cutoff.
(Shutdown upon insufficient dif-
ference between two samples.)
MOUNTING
Three NEMA-rated enclosures, de-
signed for surface mounting on any flat,
relatively stable surface free of vibra-
tion, are available for the AFS-953. The
standard enclosure has mounting
flanges with four mounting holes
(9/32") as shown in drawing on page 3.
The NEMA-4 rated model has mount-
ing flanges with four 5/16" mounting
holes as shown at top of page 4. The
NEMA-7/NEMA-9 rated enclosure has
two mounting slots as shown at bottom
of page 4. With any of the enclosures,
the AFS-953 must be mounted with
the diaphragm in a vertical plane, to
obtain the lowest operating set point
specification.
PIPING
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; Lremains open
to the atmosphere.
Negative Pressure only: Connect
sample line to L: Hremains open
to the atmosphere.
AFS-953-1 in NEMA-4 rated
Enclosure.
AFS-953 in Standard
Enclosure, rated NEMA-1.
AFS-953-2 in NEMA-7 and
NEMA-9 rated Enclosure.
Cleveland Controls
Division of UniControl Inc.
Adjustable Set Point Air Pressure Sensing Switch with 20-Second Pre-Purge and 8-Second Time Delay
Tel: [phone]
Fax: [phone]
Email:[email protected]
Web page: http://www.clevelandcontrols.com
Cleveland Controls
Division of UniControl Inc.
1111 Brookpark Rd
Cleveland OH 44109

Two Negative Samples:
Connect higher negative sample to
L,lower negative sample to H.
Two Positive Samples: Connect higher positive sample to
H, lower positive sample to L.
One Negative and One Positive Sample: Connect positive
sample line to H, 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, at-
tach an elbow to it so that the open end of the connector points
downward. This will help protect the switch from contamina-
tion.
ELECTRICAL CONNECTIONS
Five numbered terminals are provided for field wiring. Ter-
minals are pressure clamp screw type.
SEQUENCE OF OPERATION
Before pressure and power are applied to the AFS-953, the
SPDT switch contacts are in the normally closed position as
shown in Figure 2(“shelf” condition); relay contacts T-T
(TD-1) and 3-4 (TD-2) are open . When the sample lines are
connected as shown in Figure 1, and power is applied to
terminals 1 and 2, the following sequence occurs.
The pre-purge period (20 seconds) commences: the red lamp
is off. The TD1 time delay is energized. The 20-second timing
sequence commences.
At the end of the 20-second timing sequence, T-T contacts
close.
If, at the end of the 20-second timing sequence the switch is
below set point, the SPDT contacts are in NC position, the
red light comes on, the relay contacts 3 and 4 remain open,
and T-T contacts remain closed. This condition is “alarm
mode.”
If, at the end of the 20-second timing sequence the switch is
above set point, the SPDT contacts are in NO position, the
red light does not come on, the TD2 time delay is energized
and the 8-second timing cycle commences. Relay contacts
3 and 4 remain open during the 8-second cycle. After the 8-sec-
ond cycle is completed, contacts 3 and 4 close. T-T contacts
remain closed. This condition is “operating mode.”
Whenever differential pressure drops below the set point, the
SPDT switch contacts change to NC immediately, turning the
red lamp on, and de-energizing the TD2 time delay, which
starts the 8-second timing sequence. The relay contacts 3 and
4 remain closed unless the 8-second timing sequence is com-
pleted: differential pressure must remain below set point for
8 seconds continuously to complete the sequence. After this
8-second period, TD-2 relay contacts 3 and 4 open: the switch
is in “alarm mode.”
When the differential pressure becomes greater than set point,
the SPDT switch contacts change to NO immediately, turning
the red lamp off, and energizing the TD2 time delay. The dif-
ferential pressure must remain greater than set point for 8 sec-
onds continuously before the TD2 time delay closes contacts
3 and 4, returning the switch to normal “operating mode.”
FIELD ADJUSTMENTS
For the standard NEMA-1 enclosure, field adjustments to the
operating set point are made by removing the protective plug
button on the side of the enclosure and inserting a standard
blade-type screwdriver, at least 3 inches long. For the NEMA-4
and NEMA-7/9 enclosures, it is necessary to open the enclo-
AFS-953 Contact Configurations T - T
(TD-1) 3 - 4 (TD-2) Red Light
1. On Shelf Contact Positions before power is applied
Figure 2 shows AFS-953 in "on shelf"
condition: before power is applied to the
circuit and before pressure is applied to
diaphragm.
open open off
2. Pre-purge Contact Positions
During initial 20-second period after power is applied: contacts TT stay
open. (TD-1)
Power Applied; Differential Pressure
below Set Point (Immediate). open open off
Power Applied; Differential Pressure
above Set Point (Immediate). open open off
During initial 20-second period after power is applied: contacts 3-4 also
stay open., even after 8-seconds have elapsed (TD-2) .
Power Applied; Differential Pressure
below Set Point (After 8 seconds). open open off
Power Applied; Differential Pressure
above Set Point (After 8 seconds). open open off
3. Purged Contact Positions
After 20 seconds with power applied contacts TT (TD-1 ) close, and
remain closed unless power is interrupted.
Differential Pressure below Set Point
(Immediate). closed open on
Differential Pressure above SetPoint
(Immediate). closed open off
After 8 seconds (a total of 28 seconds of uninterrupted operation),
contacts 3-4 (TD-2) can change state.
Differential Pressure below Set Point
(after 8 seconds.) closed open on
Differential Pressure above Set Point
(after 8 seconds.) closed closed off
Power interrupted. Prepurge cycle repeats.
sure to make adjustments. The adjustment range is
0.05±.02" w.c. to 12.0" w.c. To adjust the set point, turn the
adjusting screw counterclockwise until motion has stopped.
Next, turn the adjusting screw 4 complete turns in a clock-
wise 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
differential. Please note: To properly calibrate an air pres-
sure sensing switch, a digital manometer or other measuring
device should be used to confirm the actual set point.

ModelAFS-953 in Standard NEMA-1 rated housing:
•Coated steel finish.
•Shipping Weight: 5 lbs.
Figure 2: “Shelf” Condition: AFS-953 contacts
before pressure amd power are applied.
MODEL AFS-953 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: 0Fto 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:
3 amps at 115 V AC at 50/60 Hz.
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 - 953 (std. enclosure): 5 lbs.
AFS - 953 - 1 NEMA 4 enclosure: 8 lbs.
AFS - 953 - 2 NEMA 7/9 enclosure: 18 lbs.
Figure 1: Sample Line Connections
L
H
H
L
H: L:
HIGH POSITIVE LOW POSITIVE
POSITIVE NEGATIVE
LOW NEGATIVE HIGH NEGATIVE
CLEVELAND CONTROLS
DIVISION OF UNICONTROL INC.
MODEL AFS-953-B
Remove Plug Button to Adjust
Turn Clockwise to Increase
Operating Set Point.
TD -1
TD - 2
Red
Signal
Lamp
Enclosure
Cover
Low Pressure Inlet
¼ NPT
High Pressure Inlet
¼ NPT
0.281” (7 mm)
mounting holes (4)
AFS-953
.875" hole
accepts
½" conduit
Plug Button
to access
adjusting
screw
1.75"
(44 mm)
4.38"
(111 mm)
3.59"
(91 mm)
5.88"
(149 mm)
5.25"
(133 mm)
1.00"
(25 mm)
6.00"
(152 mm)
2.31"
(59 mm)
1.25"
(32 mm)
8.00"
(203 mm)
3.56"
(90 mm)
1.44"
(37 mm)
R
2
1
TD-1
TD - 1
(20 SEC)
TDA-20-0
C
NC NO
LOW
PRESSURE
HIGH
PRESSURE
115 V AC
T
T
TD - 2
(8 SEC)
TDA-8-0
PREPURGE BYPASS.
INSTALL JUMPER HERE
ONLY IF SUFFICIENT
PREPURGE PERIOD IS
ALREADY PROVIDED
WITH THE BURNER
CONTROLS.
3
TO DELAYED LOW VOLTAGE
CIRCUIT OR LINE VOLTAGE
CIRCUITS. TOTAL CONNECTED
LOAD NOT TO EXCEED 2 AMPS
RESISTIVE, OR 62.5 VA PILOT
DUTY (INDUCTIVE).
TD-2

ENCLOSURE SPECIFICATIONS & DIMENSIONS
ModelAFS-953-1:
14-gauge grey hammertone enameled steel with
neoprene gasketed clamped cover hinged on the
left side. NEMA 4 rated: provides protection
from dust, dirt, oil, and water.
Shipping Weight: 8 lbs.
ModelAFS-953-2:
NOTE: Red lamp not available.
Cast aluminum alloy, nonmagnetic, non-sparking, and non-rusting. NEMA 7 and NEMA 9 rated. UL approved for Class 1, Group D; Class II,
Groups E, F, G.
Piping: Either pressure inlet, if not connected to a pressure sample, must be piped and vented to a nonhazardous area.
Shipping Weight: 18 lbs.
TD -1
(8 sec.)
TD -2
(20 sec.)
Weatherproof
Electrical
Connection
½ NPT
6.00"
(152 mm)
4.00"
(102 mm)
9.50"
(241 mm)
8.75"
(222 mm)
3.562"
(90 mm)
1.00"
(25 mm)
2.062"
(52 mm)
1.687”
(43 mm)
Red Signal
Lamp
Hinged
Cover
Low Pressure Inlet
¼ NPT
High Pressure Inlet
¼ NPT
Load Relay
0.313" (8mm)
mounting holes (4)
Timedelayre
l
a
Y
s
a
r
e
notfieldrepla
c
e
a
b
l
e
.
TD -1
(8 sec.)
TD -2
(20 sec.)
2.562"
(65 mm)
2.75"
(70 mm)
6.562"
(167 mm)
10.187"
(259 mm)
8.75"
(222
mm) 3.562"
(90 mm)
3.00"
(76 mm)
Low Pressure Inlet ¼ NPT
Mounting Slot for ½" Bolt (2)
High Pressure Inlet ¼" NPT
½" 14 NPT Electrical Connection