Series 641B Air Velocity Transmitter
9-1/4 [235.0]
1/2 NPT
POWER SUPPLY
COMMON
Y
Specications - Installation and Operating Instructions
4-31/32 [126.21]
1-23/32
[43.66]
Bulletin E-66-B
The Series 641B Air Velocity Transmitter uses a heated mass ow 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 uctuating velocities or temperatures
are present as these conditions may affect the readings. The lter 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.
Airow: 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 ow into
the transmitter housing.
ELECTRICAL CONNECTION
The 641B has been designed for easy and exible 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 exible. The device may be powered from either an
AC or DC power source.
AC OR DC
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 nal value (Output lter 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.
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.
CAUTION
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 10-16 VAC RMS. Do not exceed 20 VAC. When selecting a
transformer please note that the specied output for transformers is at some specied
current. With a load current less than the specied current transformer output may be
signicantly higher than the specied voltage. Transformers with secondary voltages
of 10 to 16 VAC are recommended.
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
RECEIVER
4-WIRE
DC SUPPLY
ONLY
(EITHER
POLARITY)
RECEIVER
3-WIRE
RECEIVER NEGATIVE
COMMON
Do not exceed the specied 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
DWYER INSTRUMENTS, INC.
Find Quality Products Online at: sales@GlobalTestSupply.com
3 or 4-wire connection
3-WIRE
RECEIVER POSITIVE
www.GlobalTestSupply.com
DC SUPPL
ONLY
(EITHER
POLARITY)
RECEIVER
CAUTION
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 elds and to some extent electromagnetic elds,
such as interference from RF transmitters. With twisted pair wiring the current loop
and the power connections should be separate pairs. Avoid using at 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 specied by the applicable code and the signal wiring must not be connected
to the conduit at more than one point or as specied 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 specied value. Provided the
power supply voltage is maintained within the specied voltage range, the 641B is not
affected by variations in power supply voltage.
Do not use transformers with a secondary voltage rating greater
than 16 VAC RMS.
TRANSMITTER SETUP
The 641B has been designed for easy setup. It has ve conguration 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 eld. These adjustments may also be easily returned to factory default.
RANGE
FPM
MPS
MPS
FPM
ABC
250
1.25
500
2.5
1000
5
2000
10
ABC
15
3000
000
100
25
5000
001
101
50
10000
010
110
75
15000
011
111
Interior label diagram
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.
Two buttons and a potentiometer control the setup process.
The SELECT button is used to scroll between the setup parameters.
The ENTER button allows access to each parameter for adjustment.
The ADJUST potentiometer is used to change the value of the parameters.
Holding the ENTER button for 2.5 seconds saves the new parameter value.
Making Adjustments
The adjustment process has three steps: select the parameter, adjust the parameter,
save the new value. These are described in the following steps.
1. Select the Parameter: Each time the SELECT button is pressed the LED
indicator will advance to the next parameter. When the last parameter, SPAN, is
selected, the next time the SELECT is pressed the unit will return to RUN mode.
Press the SELECT button until the LED indicator illuminates the desired
parameter. Press ENTER. The selected indicator will begin to blink, showing the
parameter may now be adjusted. If the unit is left in the setup mode, after several
minutes it will reset to the operate mode.
2. Adjust the Parameter: Turn the ADJUST potentiometer until the desired setting
is made. This may be adjusted using a small screwdriver or similar tool. Be
careful not to force the control past its stops or damage will result.
3. Save the Parameter: To save the new parameter press and hold the ENTER
button. The LED indicator will begin to ash at a faster rate. After about 2.5
seconds all of the LED indicators will ash when the parameter is saved. If
you do not want to save the parameter press the SELECT button without entering
the parameter. The adjusted value will be discarded and next LED indicator will
be illuminated.
Adjusting the Output Filter
The output lter may be adjusted to smooth the readings when measuring turbulent
ow. The time constant may be adjusted from 0.5 seconds to 15 seconds. To adjust the
lter time constant, select the FILTER indicator. Press ENTER to enable adjustment.
Turn the ADJUST until the desired amount of damping is achieved. To save the value
press and hold the ENTER button until the LED indicators all ash, indicating the value
was saved. To discard the adjustment press SELECT before pressing the ENTER
button.
OUTPUT FILTER RESPONSE (VALUES IN SECONDS)
Filter Setting on Adjust Dial
% of Full Velocity
63%
90%
95%
99%
Min. Mid. Max.
0.5
1.1
1.5
2.3
7.5
17.3
22.5
34.5
15
34.5
44.9
69.0
Range Selection
The range selection allows you to select one of four ranges in either feet per minute
(FPM) or meters per second (MPS).
Ranges:
FPM: 250, 500, 1000, 2000
MPS: 1.25, 2.5, 5, 10
Select the RANGE indicator by pressing ENTER when the RANGE LED indicator
is illuminated. The A,B,C LED indicators will display which range setting is currently
active. Press ENTER to enable adjustment. Turn the ADJUST until the desired range
indication is achieved. If you want to discard the adjustment press SELECT. If you
want to save the range press and hold ENTER. The RANGE LED will blink at a faster
rate for about 2.5 seconds then all of the LEDs will ash indicating the value was
saved.
The range setting is displayed with the LED indicators. The function of these indicators
is summarized on the control label inside the unit. The following table summarizes the
indicator status for each range setting.
Range/Units Run Filter Range
250 FPM
500 FPM
1000 FPM
2000 FPM
1.25 MPS
2.5 MPS
5 MPS
10 MPS
1: Indicator on
0: Indicator off
Span Setting
The 641B has been calibrated for standard sea level conditions. As a mass ow device
it will always read the air velocity for standard conditions. Density changes due to
barometric or absolute pressure are not corrected automatically. The span setting
allows correction for altitude or other static pressure conditions that affect the density
of the process air. This parameter allows for a ±50% adjustment in the span value.
To make the span adjustment you will need to know either the absolute static pressure
or the corrected velocity of the process air. Set the air velocity to a known value, ideally
about 3/4 of the full-scale range value. Press SELECT until the SPAN LED indicator is
illuminated then press ENTER. The SPAN LED will begin to blink. Adjust the control for
the desired velocity then press and hold the ENTER button until all of the LED’s ash,
indicating the new value was saved. If you know the absolute static pressure you can
compute the corrected velocity using the following equation:
Vcor = Vrdg
Where:
P0 is the standard pressure of 29.9 in Hg or 760 mm Hg.
PA is the absolute pressure reading
Vrdg is the indicated velocity
Vcor is the corrected velocity
4 mA Setting
To make this setting you will need a milliammeter connected in the current loop.
Press SELECT until the 4 mA LED indicator is illuminated then press ENTER. The
milliammeter will now read approximately 4.0 mA. Adjust the control for a 4.0 mA
reading on the milliammeter. Press and hold ENTER to save the new setting. Pressing
SELECT before pressing ENTER will restore the previous calibration value.
20 mA Setting
With the milliammeter connected in the current loop, press SELECT until the 20-mA
LED indicator is illuminated. Press ENTER to begin adjustment of the 20-mA set point.
The 20 mA LED will now be blinking. Adjust the control until the milliammeter reads
20.0 mA. Press and hold ENTER to save the new setting. Pressing SELECT before
pressing ENTER will restore the previous calibration value.
Restoring Factory Default Settings
The 4 mA, 20 mA, and Range settings override factory default values. To restore these
to the factory default settings, start with the unit in the RUN mode. Press and hold the
ENTER button. The RUN LED indicator will begin to blink. After about 2.5 seconds all
LED indicators will ash indicating the factory settings have been restored. Range and
Filter settings are not affected by this operation. If you are unsure whether any have
been altered, press the SELECT button six times to sequence through all settings.
When you return to the RUN mode, the RUN LED indicator will blink several times
if either the 4 mA, 20 mA, or span settings have been changed. The RUN LED will
otherwise remain on.
MAINTENANCE
In general the 641B should require very little maintenance. In some installations dust
may accumulate on the sensor over time. This can be removed by carefully brushing
the probe with a small camel hairbrush. A jet of air may also dislodge the accumulated
buildup. Technical grade denatured or isopropyl alcohol may be used where the dust
accumulation does not respond to brushing. Always disconnect the power when
performing a cleaning operation.
Aside from the adjustments described above, the 641B cannot be eld calibrated.
Because of specialized computer instrumentation required, these units must be
returned to Dwyer Instruments for factory calibration.
Po
PA
1
0
1
0
1
0
1
0
0
1
0
1
0
1
0
1
Span 4 mA 20 mA
A B C
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
0
0
0
1
1
0
1
1
0
0
0
1
1
0
1
1
Printed in U.S.A. 10/19 FR# 443205-20 Rev. 1©Copyright 2019 Dwyer Instruments, Inc.
DWYER INSTRUMENTS, INC.
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