User Manual

Series 641B Air Velocity Transmitter
Specifications - Installation and Operating Instructions
Bulletin E-66-B
DWYER INSTRUMENTS, INC. Phone: [phone] www.dwyer-inst.com
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46361, U.S.A. Fax: [phone] e-mail: [e-mail]
The Series 641B Air Velocity Transmitter uses a heated
mass flow sensor technology. It has 4 user selectable
ranges from 250 FPM to 2000 FPM with corresponding
metric ranges of 1.25 MPS to 10 MPS. The 641B provides
an isolated 4-20 mA output proportional to the velocity.
INSTALLATION
Location: Select a location where the temperature will be
within 32 to 140°F (0 to 60°C). The transmitter may be
located any distance from the receiver provided that the
total loop resistance does not exceed 600 ohms. The
probe should be located where conditions are representa-
tive of the overall environment being monitored. Avoid loca-
tions where turbulence, stagnation, or rapidly fluctuating
velocities or temperatures are present as these conditions
may affect the readings. The filter setting may be used to
average velocity readings in turbulent conditions.
Position: The transmitter is not position sensitive and may
be mounted in any orientation.
Mounting: The 641B should be connected to conduit or
other connection means with the 1/2˝ NPT conduit con-
nection. Ensure connection is installed properly so that dust
and debris can not enter housing.
Airflow: The 641B is intended for use with dry air. Dust
accumulation on sensor may impair the velocity measure-
ment and will require probe cleaning.
See maintenance section for additional cleaning details.
SPECIFICATIONS
Service: Air and compatible, non-combustible gases.
Accuracy:
5% FS Process gas: 32 to 122° F (0 to 50°C).
6% FS Process gas: -40 to 32°F & 122 to 176°F
(-40 to 0°C & 50 to 80°C).
Response Time: Flow: 1.5 seconds to 95% of final value
(Output filter set to minimum).
Temperature Limits: Process: -40 to 176°F (-40 to
80°C). Ambient: 32 to 140°F (0 to 60°C).
Humidity Limit: Non-Condensing.
Power Requirements: 12–35 VDC, 10–16 VAC.
Output Signal: 4-20 mA, isolated 24V source, 3 or
4-wire connection.
Output Filter: Selectable 0.5 –15 (seconds).
Loop Resistance: 600 ohms max.
Current Consumption: 300 mA max*.
Electrical Connections: Screw terminal.
Enclosure Rating: Designed to meet NEMA 4X.
Mounting Orientation: Unit not position sensitive.
Weight: 12.6 oz (357.2 g).
* A brief current transient exceeding 300 mA may be seen
on startup.
9-1/4
[235.0]
4-31/32
[126.21]
1/2 NPT
1-23/32
[43.66]
641B bulletin 2/8/05 11:04 AM Page 1