Series 641B Air Velocity Transmitter
Specifications - Installation and Operating Instructions
Bulletin E-66-B
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 Ω. 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.
See maintenance section for additional cleaning details.
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 24 V 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
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 24 V source, 3 or 4-wire connection.
Output Filter:
Selectable 0.5-15 (s).
Loop Resistance:
600 Ω max.
Current Consumption:
300 mA max*.
Electrical Connections:
Screw terminal.
Enclosure Rating:
Designed to meet NEMA 4X for non-LED models only.
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]
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.
CAUTION
POWER SUPPLY
AC OR DC
RECEIVER
4-WIRE
3-WIRE
RECEIVER NEGATIVE
COMMON
RECEIVER
DC SUPPLY
ONLY
(EITHER
POLARITY)
3-WIRE
RECEIVER POSITIVE
COMMON
RECEIVER
DC SUPPLY
ONLY
(EITHER
POLARITY)
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 Ω.
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 10-16 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.
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 Ω, 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.
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.
CAUTION
Do not use transformers with a secondary voltage rating greater
than 16 VAC RMS.
CAUTION
DWYER INSTRUMENTS, INC.
P.O. BOX 373 • MICHIGAN CITY, INDIANA 46360, U.S.A.
Phone: 219/879-8000
Fax: 219/872-9057
www.dwyer-inst.com
e-mail: [email protected]
