KAH - Air Velocity Sensor

KAH Air Velocity Sensor for Duct and HVAC Measurement

The KAH is a hot film anemometer air velocity sensor designed for ventilation control in HVAC and process or environmental control systems. It mounts through the duct wall on a supplied clamp bracket, measures 0 to 2000, 3000, or 4000 ft/min (0 to 10, 15, or 20 m/s), and delivers a 4-20 mA or 0-10 V signal from a 24 VAC/DC supply.

The thin film sensing element is designed to maintain accuracy at low air velocity, which conventional anemometers built around commercial temperature sensors or NTC bead thermistors typically cannot match. The hot film principle is also designed to be less sensitive to dust and dirt than other anemometer principles, and the polycarbonate KAH is designed for reliable, low-maintenance operation.

How the KAH Measures Air Velocity

The KAH measures air velocity (mass flow) with a specially developed thin film sensor element operating on the hot film anemometer principle. The construction of the sensor head gives the measurement low angular dependence, less than 3% of reading at flow angles within 10°, which allows easy mounting.

Response time τ90 (the time to reach 90% of a step change in air velocity) is selectable: SLOW, approximately 4 seconds (factory setting), or FAST, approximately 1 second at constant temperature.

Measuring Range, Accuracy, and Output Signal

Three working ranges are selectable by jumper: 0 to 2000 ft/min (0 to 10 m/s), 0 to 3000 ft/min (0 to 15 m/s), and 0 to 4000 ft/min (0 to 20 m/s), with 0 to 4000 ft/min as the factory setting. Accuracy from 40 ft/min (0.2 m/s) to full scale is ±(40 ft/min + 3% of reading) at 68 °F (20 °C), 45% RH, and 0 psig.

The output signal is also set by jumper: 0-10 V with output current between -1 mA and 1 mA (factory setting), or 4-20 mA into a load resistance below 450 Ω. The power supply is 24 VAC/DC ±20% (SELV), with current consumption of at most 170 mA on AC and 70 mA on DC.

KAH Specifications

• Working range: 0 to 2000 / 3000 / 4000 ft/min (0 to 10 / 15 / 20 m/s), jumper-selectable
• Output signal: 0-10 V or 4-20 mA (RL < 450 Ω), jumper-selectable
• Power supply: 24 VAC/DC ±20%
• Response time τ90: approximately 4 s (SLOW) or 1 s (FAST)
• Probe length: 7.87 in (200 mm); clamp for duct mounting
• Working temperature, probe: -13 to 122 °F (-25 to 50 °C)
• Working temperature, electronics: 14 to 122 °F (-10 to 50 °C)
• Storage temperature: -22 to 140 °F (-30 to 60 °C)
• Humidity: 5 to 95% RH, non-condensing
• Operating pressure: maximum 2.9 psi (200 mbar)
• Housing: polycarbonate, UL94V-0 approved; IP65 (NEMA 4)
• Electromagnetic compatibility: EN 61326-1, EN 61326-2-3

Installing the KAH in a Duct

The KAH mounts through the duct wall on the included mounting bracket, which allows the probe insertion depth to be adjusted infinitely. Mount the sensor so that the direction of airflow runs parallel to the sensor duct in the probe head, and complete the installation with power off.

Install the sensor in the middle of the duct at a position with laminar (non-turbulent) flow; the preferred position is after a filter. Turbulence appears after fans, bends, junctions, flaps, heaters, coolers, filters, and diameter changes, so allow at least 6D of straight duct downstream of a disturbance and 3D upstream of the next one, where D is the duct diameter. Ahead of a diffuser, place the sensor at the position of high air velocity. For a rectangular duct a × b, D = 2 × a × b / (a + b).

Wiring and Jumper Settings

Wiring uses three screw terminals: terminal 1 (V+) for the 24 VAC/DC supply, terminal 2 (GND) for system neutral or ground, and terminal 3 (AV) for the analog air velocity output. The terminals accept wire up to AWG 16 (1.5 mm²), and cable enters through an M16 × 1.5 gland.

Three jumper positions on the circuit board set the output type (U for voltage, I for current), the working range (LO, MED, or HI for 0 to 2000, 3000, or 4000 ft/min), and the response time (jumper on t90 for SLOW, no jumper for FAST). The factory settings are voltage output, the HI range, and SLOW response.

Common Questions about KAH - Air Velocity Sensor