Series-641

Supported Applications

The Dwyer Series 641 Air Velocity Transmitter (AVT) utilizes heated mass flow sensor technology to monitor air velocity in clean, dry environments. The series is designed for use with clean air and compatible, non-combustible gases. It provides precise velocity measurements across a wide range of flow rates suitable for various airflow monitoring tasks.

Note: Particulates may cause sensor damage or impair measurement accuracy; dust accumulation requires probe cleaning. The transmitter is not position sensitive and can be mounted in any orientation, provided the probe is aligned with the direction of airflow.

Operating Conditions & Performance

The Series 641 operates within an ambient temperature range of 32 to 140°F (0 to 60°C). The process gas temperature limits are defined as follows:

• -40 to 212°F (-40 to 100°C)

Accuracy specifications vary by process gas temperature range:

• 3% FS: Process gas at 32 to 122°F (0 to 50°C).
• 4% FS: Process gas at -40 to 32°F and 122 to 212°F (-40 to 0°C and 50 to 100°C).

The measurement range spans from 250 FPM (1.25 MPS) to 15,000 FPM (75 MPS). Resolution is specified as 1 FPM, 0.01 MPS, with a resolution of 10 FPM at the 10,000 and 15,000 FPM ranges. The response time for flow is 1.5 s to 95% of final value when the output filter is set to minimum.

The unit features a maximum pressure rating of 100 psi (6.89 bar). Humidity conditions must be non-condensing. Non-LED models are designed to meet NEMA 4X (IP66).

Configuration Options

The Series 641 offers configurable probe lengths and optional local indication features.

• Probe Lengths: Standard models include 6" (152.4 mm), 12" (304.8 mm), 18" (457.2 mm), and 24" (609.6 mm). Other probe lengths are available upon contacting the factory.
• Ranges: The transmitter provides 16 field-selectable ranges, including eight user-selectable imperial ranges from 250 FPM to 15,000 FPM and corresponding metric ranges from 1.25 MPS to 75 MPS.
• Output Signal: Provides an isolated 4-20 mA output with a built-in isolated 24 V source, supporting either a 3-wire or 4-wire connection. Maximum load resistance is 600 Ω max.
• Power Supply: Requires 12-35 VDC or 10-16 VAC. A supply rating of 1.5A is required due to the initial power surge drawn by the transmitter.
• Process Connection: Features a 1/2" male NPT connection.
• Electrical Connection: Utilizes screw terminals. Where conduit connections are not made, a 1/2" NPT cable seal should be used to prevent contaminants from entering the case.

The series supports an optional 1/2" 4-1/2 digit LED display for local readout of velocity. This option is available as a field-upgradeable accessory (model 641-LED).

Accessories and Options

• A-156: Universal mounting plate, 1/2" female NPT.
• A-158: Split flange mounting kit.
• A-159: Duct mounting gland.
• -NIST Suffix: Adds a NIST traceable calibration certificate to the order.

Key Product Differences

The Series 641 is distinguished by probe length and display configuration. Model numbers follow the format 641-, with an optional suffix for the LED version (e.g., 641-12-LED). The series includes variants without a display option, which are designed to meet NEMA 4X (IP66) ratings. Models equipped with the optional LED display have different dimensional profiles compared to non-display models.

Dimensions: Overall dimensions vary by probe length and presence of the display option. For example, a model without the display ranges from A Dimension 7-7/16 [188.91] to 37-7/16 [950.91], while models with the display range from A Dimension 7-63/64 [202.80] to 37-63/64 [964.80]. Weights are listed as 12.6 oz (357.2 g) for standard models and 13.3 oz (377 g) for the optional display version.

Note: The Series 641 AVT cannot be fully factory calibrated in the field; units must be returned to Dwyer Instruments for calibration using specialized computer instrumentation.