Characteristics of velocity sensors
Adapted from ASHRAE 1997
Measurement Means |
Application |
Range |
Precision |
Limitations |
|
ft/min | m/s | ||||
Smoke puff or airborne solid tracer |
Low air velocities in rooms; highly directional |
5 to 50 | 0.025 to 0.25 |
10 to 20% |
Awkward to use but valuable in tracing air movement |
Deflecting vane anemometer |
Air velocities in rooms, at outlets, etc.; directional |
30 to 24,000 | 0.15 to 120 |
5% |
Needs periodic check calibration |
Revolving vane anemometer |
Moderate air velocities in ducts and rooms; somewhat directional |
100 to 3000 | 0.5 to 15 |
2 to 5% |
Extremely subject to error with variations in velocities with space or time; easily damaged; needs periodic calibration |
Hot-wire anemometer |
a. Low air velocities; directional and nondirectional available |
1 to 2000 | 0.005 to 5 |
2 to 5% |
Requires accurate calibration at frequent intervals. Some are relatively costly. |
b. High air velocities |
Up to 60,000 | Up to 300 |
0.2 to 5% |
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c. Transient velocity and turbulence |
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Measurement Means |
Application |
Range |
Precision |
Limitations |
|
ft/min | m/s | ||||
Pitot tube |
Standard instrument for measuring duct velocities |
180 to 10,000 with micromanometer; 600 to 10,000 with draft gages; 10,000 and up with manometer |
0.9 to 50 with micromanometer; |
1 to 5% |
Accuracy falls off at low end of range |
Impact tube and sidewall or other static tap |
High velocities, small tubes and where air direction may be variable |
180 to 10,000 with micromanometer; 600 to 10,000 with draft gages; 10,000 and up with manometer |
0.6 to 50 with micromanometer; |
1 to 5% |
Accuracy depends on constancy of static pressure across stream section |
Cup anemometer |
Meteorological |
Up to 12,000 | Up to 60 |
2 to 5% |
Poor accuracy at low air velocity (< 500 fpm, [<2.5 m/s]) |
Laser Doppler velocimeter |
Calibration of air velocity instruments |
1 to 6000 | 0.005 to 30 |
1 to 3% |
High cost and complexity limit LDVs to laboratory applications |