M-46
AC Axial-flow Fans
Common Information
Noise Measurements
The following two methods are available for measuring Fan noise.
These are used interchangeably by Fan manufacturers so that the
measurement method is not standardized.
JIS B 8330: Testing and Inspection Methods for Fans
JIS C 9603: Extractor Fans
OMRON conducts testing according to JIS (Japan Industrial Stan-
dard) C 9603 because of the small size and low noise levels of the
Fans and because of their similarity in shape to extractor fans. This
standard prescribes that the noise be measured at a distance of 1 m
from the side of the Fan.
Selecting a Fan
Follow the steps below to select Fans.
1. Procedure
(1) Estimate the amount of heat generated inside the Unit.
(2) Set the maximum permitted temperature rise limit inside the Unit.
T
1
: Temperature of the inlet air (
°
C).
T
2
: Temperature of the outlet air (
°
C).
(3) Calculate the required flow rate.
Q = 50W/
∆
T (m
3
/min)
Q = flow rate (m
3
/min.)
∆
T = permitted temperature rise limit (
°
C)
(Normally between 8 to 10
°
C.)
W = amount of heat generated (kW)
(4) Estimate the system impedance from the air flow through the Unit
or from previous data.
∆
P = KQ
n
∆
P: Pressure drop (Pa)
K: Unit constant
n: Coefficient determined by air flow
n=1: laminar flow
n=2: turbulent flow
(n=2 is the normal value.)
(5) Select the Fan according to the P - Q characteristics.
(6) Measure the temperature rise in an installed Unit.
(7) Reappraise the Fan if the measured cooling effect is insufficient.
Flow Rate Measurement Device
Mesh to smooth flow
Chamber selector
Nozzle Mesh to smooth flow
Damper
Auxiliary blower
AIR
Chamber A
Chamber B
Manometer to measure static pressure
(digital pressure-gauge on machine)
Manometer to measure static pressure (digital pressure-gauge on machine)
Measure pressure difference across nozzle (difference between chamber A
and B pressures) and calculate air flow rate.
Measured fan
AIR
Sample Flow Rate/Static Pressure Characteristic
Static pressure:
Ps (P
a
)
Max. pressure: Ps max.
Measurement
point
Fan operating point
when installed in
machine
Intermediate range (Q, Ps)
Max.
flow
rate:
Qmax.
System impedance
of unit
Flow rate: Q (m
3
/min)
1 m
1 m
Fan
Microphone
T
1
T
2
Power
supply
