SKC Limited AirChek 3000 Deluxe Pump Step By Step Guide - Manual (Page 11)

www.skcltd.com 224-G1 Issue D Page 9
Calibration
Calibration of the flow through the sampling
system is important and should be checked
before AND after every sample is taken.
Broadly speaking there are two different levels
of flow commonly used for personal sampling
systems. For dust the flow is often set at
around 2 litres per minute and for gases and
vapours between 10 and 200 ml per minute.
The usual method of flow measurement
(calibration) for the higher flows is achieved
using a rotameter (variable area flowmeter).
Both 2 litres per minute for inhalable dust using
the I.O.M. sampler and 2.2 litres per minute for
respirable dust using the cyclone sampler can
be set using this type of device. The flow is
read from the float inside the graduated glass
tube.
For the lower flows of between 10-200 ml per
minute normally required for gases, a bubble
film calibrator is suitable. This unit has high
accuracy and low back pressure with superior
resolution compared with the rotameter
mentioned above. The flow is calculated
by timing a bubble between two graduation
marks on a glass tube with a stopwatch.
A third alternative is to use an electronic
calibrator, such as the Defender primary
calibrator, which operates on the same principal
as the bubble film calibrator but it electronically
detects and times a passing piston. An LCD
screen shows the flow measured.
This instrument has a much larger range than
the manually timed bubble film or rotameter
devices and typically covers from 50-5000
ml/min. Its accuracy is also better than the
manually timed version across the entire range.
Rotameters
0
5
0
5
0
5
3
3
2
2
1
1
0
0
Effective
Range
80%
20%
Error
Eye Level
2
2
1
1
5
0
5
0
2
2
1
1
5
0
5
0
Read Here Read Here
Ball Type Float Type
Bubble Film Calibrator
Defender Primary Calibrator
10°C change in temperature =
1% change in rotameter reading
On a 100mm scale rotameter the
thickness of the graduation line =
approximately 3% of the total scale