A-A-50624
c. Response time. When operated in a standard one-atmosphere ambient environment with an airflow velocity of 25 percent of full-scale, the airflow monitoring system shall achieve a full-accuracy output signal and full accuracy display readout within 12 seconds for an airflow velocity step increase of from 30 to 75 percent full-scale.
d. Repeatability. Airflow monitoring system repeatability shall be two within ± 1.5 percent of full-scale.
2. Airflow sensor.
a. Required operating principle. The sensor shall employ a thermal anemometer technique for sensing airflow.
b. Physical characteristics. The sensor shall consist of a cylindrical probe and an attached/integral electronics processing package. The sensor probe shall be constructed of corrosion resistant material. The sensor probe shall be from 1.0 cm to 2.6 cm in outside diameter. The probe length shall be appropriate for the cylindrical or rectangular duct size as specified. A mounting plate shall be provided to secure the sensor to the air duct. The sensor shall be readily removable from the mounting plate (to facilitate periodic cleaning).
c. Power input. The airflow sensor shall be powered by +15 to + 18 Vdc and shall draw no more than 350 mA.
d. Airflow Range. The airflow velocity range of the sensor shall be from zero mps to the full-scale mps value as specified.
e. Output signal. The airflow sensor shall output a 4-20 mA signal linearly proportional to airflow velocity. A 4 mA output shall correspond to zero airflow velocity and a 20 mA output shall correspond to full-scale airflow velocity. The sensor shall drive a resistive load of 250 ohms ± 5 percent.
f. Accuracy. The airflow velocity output signal shall be accurate to within ± (3.0 percent of reading plus 1 percent of full-scale).
g. Repeatability. Repeatability shall be to within ± 0.5 percent of full-scale.
h. Response time, velocity change. When operating in a standard one-atmosphere environment and an airflow velocity of 25 percent full-scale; the airflow sensor shall achieve a full-accuracy output signal within 10 seconds for an airflow velocity step increase to 75 percent full-scale.
i. Response time, temperature change. When operated in a standard one-atmosphere environment and an airflow velocity of 50 percent full-scale; the airflow sensor shall achieve a full-accuracy output signal within four minutes for a 20 degrees Celsius (oC) temperature step increase.
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