Dwyer Instruments 641B Operating Manual

1/2 NPT

1-23/32

[43.66]

Bulletin E-66-B

Series 641B Air Velocity Transmitter

Specifications - Installation and Operating Instructions

9-1/4

[235.0]

4-31/32

[126.21]

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 representa­tive of the overall environment being monitored. Avoid loca­tions 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 con­nection. 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 measure­ment and will require probe cleaning.

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.

See maintenance section for additional cleaning details.

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]

Page 2

NOTE: Where conduit connections are not made, a 1/2˝

NPT cable seal should be used to prevent contaminants
from entering the case. Where conduit connections are
made, make sure that any possible condensation within the
conduit will not flow into the transmitter housing.

ELECTRICAL CONNECTION

The 641B has been designed for easy and flexible connec­tion to power and loop receivers. Electrical connection is
made inside the body of the device with a “Euro” style ter­minal block. The device features a current loop that is fully
isolated from the power source. The current loop has an
internal 24V isolated supply so no external loop power is
required. With full isolation, loop grounding is not a concern.
The input power requirements are also very flexible. The
device may be powered from either an AC or DC power
source.

3 or 4-Wire Connection

POWER SUPPLY

AC OR DC

RECEIVER

4-WIRE

DC SUPPLY

ONLY

(EITHER

POLARITY)

RECEIVER

3-WIRE

RECEIVER NEGATIVE

COMMON

DC SUPPLY

ONLY

(EITHER

POLARITY)

RECEIVER

3-WIRE

RECEIVER POSITIVE

COMMON

CAUTION: Do not exceed the specified supply voltage rat­ing. Permanent damage not covered by the warranty may
result. Do not use an external power source on the current
loop connection.

Receiver-Transmitter Connection — The 641B is
designed as a three or four wire 4-20 ma device. The cur­rent loop output is isolated from the power supply input and
provides an internal 24-volt loop supply. With a DC power
supply, a three or four-wire connection may be used. Do not
use a three-wire connection with an AC power source. In a
three-wire connection either power supply wire may be
used as the common. The total loop resistance should not
exceed 600 Ohms.

Wire Type and Length — The wire selection for an instal­lation is often overlooked or neglected and may contribute
to improper or even intermittent operation. In all cases
ensure that the connection meets all applicable national
and local electrical codes. Although the 4-20 mA current
loop systems are relatively immune to wire or wiring related
problems, selection of the wire for some installations will be
an important factor in ensuring satisfactory system opera­tion. Twisted conductors will usually be immune to most
stray electric and magnetic fields and to some extent elec­tromagnetic fields, such as interference from RF transmit­ters. With twisted pair wiring the current loop and the
power connections should be separate pairs. Avoid using
flat or ribbon cable that has no regular conductor twist.
Where interference is possible, it is recommended that
shielded wire be used. The shield must not be used as one
of the conductors and should be connected to ground at
only one end, generally at the power supply. Similarly, if the
installation uses conduit, the conduit should be connected
to protective ground as specified by the applicable code
and the signal wiring must not be connected to the conduit
at more than one point or as specified by the code.
The maximum length of wire connecting the transmitter
and receiver is a function of the wire resistance and receiv­er resistance. The total loop resistance must not exceed
600 Ohms, including the receiver resistance and wire resis­tance. The power supply connection must be designed so
that the worst case voltage drop due to wire resistance will
not cause the power supply voltage at the transmitter to
drop below the specified value. Provided the power supply
voltage is maintained within the specified voltage range, the
641B is not affected by variations in power supply voltage.

TRANSMITTER SETUP

The 641B has been designed for easy setup. It has five
configuration parameters that may be adjusted by the user.
These parameters are Output Filter, Range (In English or
Metric), span, 4 mA set-point and 20 mA set-point. All of
these may be adjusted at any time in the field. These
adjustments may also be easily returned to factory default.

Interior Label Diagram

CAUTION: Do not use a receiver with an internal power

supply or use an external supply in the current loop. The
current loop is powered from within the 641B. Connecting
an external supply to the current loop may destroy the
transmitter. Using an external supply voids the warranty.

Power Supply Connection — The power supply may be
either AC or DC. The DC power may be from 12 to 35 Volts.
The power connection is not polarity sensitive so the posi­tive and negative connections may be made to either power
terminal. The AC connection may be from 10 to 16 VAC
RMS. Do not exceed 20 VAC. When selecting a transformer
please note that the specified output for transformers is at
some specified current. With a load current less than the
specified current transformer output may be significantly
higher than the specified voltage. Transformers with sec­ondary voltages of 10 to 16 VAC are recommended.

CAUTION: Do not use transformers with a secondary volt­age rating greater than 16 VAC RMS.

A set of controls and indicators are provided within the unit
consisting of the select button, enter button, adjustment
control, and six LED indicators. When operating normally,
only the RUN LED indicator will be illuminated. During the
setup operation the LED indicators will indicate the para­meter selected, when it is being adjusted, and status of the
adjustment process. If the unit is left in the setup mode for
several minutes without any activity it will return to the
normal operating mode.