Ahlborn ALMEMO 2390-5 Manual de Serviço descarregar pdf (Página 21)

Volume Flow Measurement

3.5.5 Volume Flow Measurement

For determining the volume flow V in ventilating channels the medium flow ve-

locity is multiplied with the cross section area F:

V = v

F 0.36 V = volume flow in m

/h,

F = cross section in cm

= medium flow velocity in m/s

Air Volume Measurement with Mountable Hopper

For air volume measurement at air vents (e.g. disk valve) up to 200mm dia-

meter the mountable hopper ZV 9915-LM is available for the macro rotating

vane FV A915-MA1 as an accessory. By scaling the air velocity with the factor

1.3762, exponent +1 and dimension mh the air volume is obtained in m3/h. A

correction factor for the forced circulation of the rotating vane is already con-

sidered. The measuring variable volume flow can also be programmed as 2nd

channel.

Chan. Function Meas. Range Dim Range Factor Exp

1st ch.: air velocity 0.2...20.00 m/s ms L420 - -

2nd ch.: volume flow 1.0...275.0 m3/h mh L420 1,376 +1

Volume Flow Measurement with Center Probe

For a rough measurement of the volume flow it is sufficient to place a flow

probe in the center of the flow channel. The medium flow velocity is approxim-

ately 0.8 v (see below 'net measurement center method'). By scaling the velo-

city with the factor (0.8 F 0.36) the momentary volume flow can be continu-

ously indicated in m3/h. It may be also necessary to program the exponent and

the dimension.

Determining a Volume Flow from Average Value & Cross Section

To obtain measured values as accurately as possible, the flow velocity must be

integrated and averaged over the whole area. The hand-held devices 2390-5,

2690-8, 2890-9 and system 5690-2 allow for entering the cross section area

directly via keyboard in function QF, as area F with 32000cm2 at maximum, or

in the function DN via the diameter with 2000mm at maximum. The volume

flow V can then be read out in function channel “Flow” directly in m3/h - the

product of average value and surface; (see device instructions, “Volume flow

measurement”).

It is also possible, by means of function channels “Flow” and “n(t)”, to output

and to save the volume flow and the number of measuring operations; (see

Section 6.3.3).

ALMEMO

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