8-24 Model 3775 Condensation Particle Counter
entered into the instrument memory through the serial port. The
calibrated flow value is displayed on the instrument Status screen
(
Figure 4-9) and is used for calculation of particle concentration.
When the orifice becomes contaminated or is replaced, a new orifice
calibration can be performed, and a new flow calibration data can
be entered by the user. Note however, as discussed in the section
“
Maintanence of the Critical Orifice”, orifices supplied by TSI have
good repeatability. Unless you have a high accuacy flowmeter
(<±2%) for calibration, it may be preferable not to recalibrate.
Orifice Calibration
1. Turn the instrument on and allow to warm up.
2. Select the Inlet Flow Mode of 0.3 L/min from the User Settings
menu (see
Figure 4-5).
3. Connect your “bubble meter”, TSI flowmeter, or similar high-
accuracy, low resistance flowmeter to the CPC inlet.
4. Deterimine the volumetric flow rate at the inlet.
5. Refer to the infromation on RS-232 serial communications
provided in
Chapter 7. To send specific calibration data to the
instrument serial port, you will need to use a a program capable
of sending and receiving ASCII commands such as
“HyperTerminal” supplied with Windows
®
and described in the
“Command” section.
6. Connect your computer to the serial port (Serial 1) at the back
of the CPC instrument.
7. Type in the serial command for changing the 3775 aerosol flow
rate "SAF,x", if necessary, where x is the flow rate in cm
3
/min.
The value entered should be very close to 300 cm
3
/min.
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