Setup and Operation
2–3
Figure 2-1
Back Panel of the CNC:
a
fill connector,
b
drain connector,
c
vacuum exhaust,
d
power
Flow Control—
Vacuum Source
*Flexible
1
/
2
-inch OD and
1
/
4
-inch ID tubing is recommended.
The CNC flow, controlled by a critical orifice inside the instrument, requires an
external vacuum source, such as the plant vacuum or central vacuum or a vacuum
pump outside the clean area. Connect the vacuum tubing* between the vacuum
source and the exit port on the back panel of the CNC. The CNC requires a
minimum vacuum pressure of 18 inches of mercury and draws a total flowrate of
0.1 scfm. Only 0.05 cfm makes up the sample flowstream. The remaining airflow
is purge air for the cabinet.
To measure the instrument’s flowrate, connect a low-pressure-drop flowmeter to
the CNC’s inlet. A bubble meter or thermal flowmeter (such as TSI’s Model
2011B) works best. The flowrate should be 0.05 cfm (1.415 L/min) ±10 percent. If
the flowrate is too low, the orifice may be plugged, the vacuum may be less than
18 inches of mercury, or the pressure drop of the test flowmeter may be too high.
If you suspect a clogged orifice, contact TSI to learn how to correct this.
Caution
:
If you are using a vacuum pump, the vacuum exhaust containing
malodorous butanol vapors should be channeled to a hood ventilator
or to an absorbent. Do not exhaust the vapors into an unventilated
area.