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**** REPLACED BY SERIES 641 ****

Series 640 - Air Velocity Transmitter

Four Field Selectable Ranges from 0-200 to 0-12,000 FPM
Linear, 4-20 mA Output Signal, ±2% Accuracy at an Affordable Cost
Rugged steel NEMA 13 housing with 12" stainless steel probe on 6' connecting cable. Liquid tight cable entrances.

The Dwyer Series 640 air velocity transmitter is ideal for a wide range of HVAC measurement and control applications, particularly in complete building control and energy management systems. Designed for use in reasonably clean and dry air streams, applications include multipoint air velocity measurements, supply and exhaust fan tracking, industrial hygiene and clean-room systems, air pollution studies and manufacturing or process control systems. See Dimensions

The Series 640 brings ±2% accuracy (including linearity, hysteresis and repeatability) to these types of demanding applications at a surprisingly low cost. With four field selectable ranges of 0-200, 0-1000, 0-3000 and 0-12,000 FPM, this single transmitter can be supplied off-the-shelf for a variety of different air velocity measurement applications.

The Series 640 transmitter is easily installed with the mounting hardware supplied, including a split flange for securing the sensing probe in the duct. Requiring only 18-24 volts AC or 22-28 volts DC for power and having a two-wire, 4-20 mA output, electrical connections are made quickly and easily by means of a four-wire cable to a plug-in terminal block through a liquid tight cable gland. The NEMA 13 housing is suitable for all indoor industrial, institutional or commercial installations. An optional probe extension is available for larger duct sizes.

The central components of the Series 640 transmitter are the velocity and temperature sensors located in the tip of the probe. The velocity sensor is a constant temperature thermistor which measures the air velocity, referenced to standard conditions, by sensing the cooling effect of the moving air passing over the heated sensor. The power required to maintain the velocity sensor temperature, as provided by the control circuitry in the electronics package, is a function of the air velocity. The velocity sensor is rugged enough to tolerate small particulate contamination and still provide fast response to changes in air velocity. A temperature sensor in the probe tip compensates for a wide range of air stream temperature variations. Each transmitter is individually calibrated at our factory in a computer controlled wind tunnel. During this calibration procedure, the inherent non-linearity of the thermistor velocity sensor is automatically corrected by appropriate programming of an EPROM in a linearizer circuit of the electronics package.


Media: Air.
Ranges: 0-200, 0-1000, 0-3000, 0-12,000 FPM (field selectable: referenced to standard conditions).

Power Supply: 18-24 VAC, 22-28 VDC.
Output Signal: 4-20 mA DC.
Loop Resistance: 0-300 Ohms.
Current Consumption: 250 mA maximum.
Warm-up Time: 3 to 5 minutes.
Zero Output: 4 mA.
Full Span Output: 20 mA.
ACCURACY: (% of F.S.)
0-200 fpm range
±5% @ 32-180°F; ±9% @ 0-32°F or 180-200°F.
0-1000, 0-3000 or 0-12,000 fpm ranges
±2% @ 32-180°F; ±6% @ 0-32°F or 180-200°F.
Temperature Ranges: Operating: -32 to 160°F; Storage: 0 to 200°F.
Weight: 3 lb.
Probe length: 12 in.
Cable length: 6 ft.
Model 640-0 Air Velocity Transmitter
A-398 Probe Extension Adapter for Series 640 Air Velocity Transmitter, brass, 1/2" female NPT x 5/16" compression.
Durable thermal velocity and temperature sensors are mounted within 5/16" dia. stainless steel probe with etched 12" insertion depth scale.
Simple field ranging by means of circuit board mounting DIP switch. Easy electrical connections made by means of four-wire cable with plug-in terminal connector.
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