DOC-0171 Rev G-9
2 2
© 2017 DROPLET MEASUREMENT TECHNOLOGIES
3.4 Turning Off the System
To turn off the SP2, follow the instructions below.
Note:
Users who have the SP2 with an Auto
Sampler and Nebulizer should consult
DOC-0318,
the
Set-up and Operation Manual for the SP2 with
Auto Sampler
for this procedure.
1.)
On the SP2 software’s
Control
tab, set the
Laser Power Switch
to Off (Figure 15).
WARNING
:
Laser Power must be turned off before the pump is turned off.
Figure 15: Turning the Laser Off
2.)
Turn off the
Sample Pump
switch on the SP2.
3.)
Shut down the SP2 software by selecting
File > Exit.
4.)
Turn off the SP2 using the
System Power
switch on the SP2.
5.)
Turn off the SP2 Computer using the
Computer
switch on the SP2.
4.0
Flow System
The SP2 requires both a source of vacuum, and of low-pressure (approximately 10 psi) dry
compressed air for operation. The instrument is supplied with a boxed diaphragm pump which
provides both functions. Appendix D, the SP2 Plumbing Diagram, provides details about the SP2-D
flow. The sample flow is measured by a Laminar Flow Element immediately ahead of the sample
jet. The sample jet uses a sheath of filtered air to narrow the aerosol stream just before the laser
beam. An additional stream of filtered purge air is injected on either end of the laser frame to
minimize the chance of aerosol particles contaminating the laser optics.
The flows of sheath air for the jet and purge air for the optics are regulated by flow controllers. The
flow controllers are mass flow controllers, but in the software the mass flow is converted to volume
flow and they are regulated as volume flow controllers. The data-acquisition card for the
housekeeping channels has only two digital-to-analog control lines. One of the lines controls the
sheath flow, and the other goes to the exhaust flow regulation, which is fed information from the
sample flow measurement. Since the amount of purge flow air is not critical, the purge flow
controller is slaved to the sheath flow controller. In normal operation, the voltage provided to the
purge flow controller is 60% of that to the sheath flow. The purge flow controller has half the range
of the sheath flow controller, so the net purge flow is 30% of the sheath flow.
