DWYER INSTRUMENTS, INC.
Phone: 219/879-8000 www.dwyer-inst.com
P.O. Box 373 • Michigan City, IN 46361-0373, U.S.A. Fax: 219/872-9057 e-mail: info@dwyer-inst.com
The Model 660 Air Velocity Monitor is an inexpensive acces-
sory for laboratory fume hoods to indicate the approximate face
velocity of airflow with the primary purpose of warning when a low
flow condition occurs. Red, green and yellow LED’s correspond to
low, normal and high flow rates. When flow decreases from nor-
mal to low an audible alarm will also actuate requiring manual
acknowledgment to silence. Settings for alarms must be individu-
ally adjusted for each fume hood because of the unique conditions
within each one and its surrounding environment. This initial cali-
bration procedure requires use of a suitable anemometer such as
a Model 480 Vaneometer
TM
, Model 471-1 Handheld Thermal
Anemometer or comparable device to measure flow rates through
the fume hood.
OPERATING PRINCIPLE
At the heart of the Model 660 AVM is a small constant tempera-
ture thermistor bead mounted in the center of the sensing tube.
As moving air changes the thermistor output, electronic circuitry
varies the current level to maintain temperature at a factory set
standard condition. By comparing the amount of current neces-
sary to maintain this standard versus normal current, velocity can
be accurately measured and indicated through the LED’s and the
audible alarm.
This unit is typically mounted on the face of one of the fume hood
sidewalls at a convenient viewing height. Flexible tubing is run to
a location, defined in Fig. B, on the interior sidewall of the fume
hood. In operation, the fume hood blower simultaneously draws
air through both the open sash area of the fume hood and the
opening in the 660 AVM. When sufficient change from the “nor-
mal” flow is detected, the lights change accordingly and if a low
flow condition occurs, the audible alarm also sounds.
CAUTION: Do Not Touch the glass enclosed thermistor bead
inside the flow tube. It is very fragile and permanent damage, not
covered by warranty, could result. See maintenance for cleaning
recommendations.
Model 660 Air Velocity Monitor
Specifications - Installation and Operating Instructions
Bulletin H-16
SPECIFICATIONS
Service: Air and non-combustible, non-corrosive gases.
High Setpoint Range: 0-275 FPM (0-1.397 m/s).
Low Setpoint Range: 0-150 FPM (0-.792 m/s).
Repeatability: ±7% of full span, 0-50 and 150-275 FPM;
±5% of full span, 50-150 FPM.
Compensated Temperature Range: 50 to 90°F (32.2°C).
Operating Temperature Range: 32 to 120°F (0 to 48.9°C).
Power Supply: 24 VAC, 3 watts maximum.
Response Time: 6-10 seconds.
Warm-Up Time: 3-5 minutes (no flow).
Audible Alarm: 75 dB between 3-10 feet.
Weight: 3 oz (85 g).
Mounting Hardware: (2) #6 x 1" sheet metal screws, (2) 6-32 x
7/8" machine screws.
INSTALLATION
Tubing, bulkhead fitting and connectors are included with this
device. This kit contains 3 ft of flexible tubing, one tube adapter
with locknut, one 90° elbow adapter and power supply. Assembly
drawing, fig. C, depicts installation using this kit.
1. Choose a clean, dry location with adequate rear space on the
fascia of fume hood side wall, adjacent to the outlet hole location.
See fig. D on reverse for full size mounting hole template. See Fig.
D on reverse for full size mounting hole template. See Fig. B for
outlet hole location.
2. Cut all openings and attach tubing between outlet hole and 660
AVM. As an alternative to flush panel mounting, a single gang
electrical box can be used to surface mount unit by cutting an
opening in the back large enough for tubing clearance. Make sure
tubing is not kinked.
3. Loosen screws on electrical terminal block behind HIGH LED
and insert power supply leads in side openings. Tighten screws,
plug in power supply to outlet. Connect wire leads to 24 VAC
power supply. On initial power application with no airflow, LED’s
will cycle from red-green-yellow-green-red with audible alarm on
red. Alarm can be silenced by pressing ACK. pad.
01-3/32
[27.76]
5/8
[15.88]
3-13/64
[81.36]
1-13/64
[30.56]
7/32
[5.56]
2-3/4
[69.85]
2-53/64
[71.83]
4-1/2
[114.30]
Fig. A
H-16:H-16 7/24/09 10:48 AM Page 1
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