Casella CEL Apex personal sampling pumps - Manual (Page 19)

19
For example, when 10 litres must be sampled over an 8-hour work shift, the pump flow can be set to run
at a flow rate of:
= 0.021 litres / min = 21 millilitres / min
10
8 x 60
For the whole shift, which is a very low flow.
On
1 min
On
1 min
On
1 min
On
1 min
On
1 min
On
1 min
On
1 min
On
1 min
On
1 min
On
1 min
02011
Run: 480 min
Exp: 10 min
TWA: 2%
Off
47 min
Off
47 min
Off
47 min
Off
47 min
Off
47 min
Off
47 min
Off
47 min
Off
47 min
Off
47 min
Off
47 min
Alternatively, the TWA mode can be used to run the pump for short periods at a higher rate, for example 1
l/min, with the pump actually running for only:
= 10 minutes during 8 hour shift
10
1
Using TWA mode, the sampling (RUN) time should be set to 8 hours
and the pump-on exposure (EXP) time to 10 minutes, as follows.
1.
Enter Configuration Mode, select Program Mode / ON and accept it
as described in Section 2.4.
The instrument reverts to Hold Mode.
2. Press or several times until TWA blinks on the display.
3. Press to select it.
RUN is displayed and the run time blinks to indicate that it can be
changed.
4. Use or to select a run time.
Sampling (RUN) durations between 3 minute and 1 hour can be set
in 1-minute steps and durations between 1 and 25 hours in 10-minute steps.
5. Press to accept the selected run time.
EXP is displayed, and the exposure time blinks to show it can be
changed.
6. Use or to select an exposure time.
The available range is from 2 minutes to “1 minute less than the run
time“, in 1-minute steps.
7. Press to accept an exposure time and start sampling.
In addition to the usual and symbols, the display shows PROG. to indicate that a program
is active.
The pump ON-times are fixed at 1 minute, and the instrument calculates the necessary OFF-times
to spread these 1 minute intervals evenly throughout the run time.
While the program is running, the display cycles through current accumulated run time, volume
sampled, air temperature and calculated TWA (as a percentage of run time).
During OFF-times (pump not running) the and symbols are displayed to show the
instrument is paused.
Once the run is completed, the pump will switch OFF and the display show the symbol and a
PROGEnd message.
Figure 10: TWA ON/OFF cycle