Standard Operating Procedure
Turbomolecular Pumping System #2
(Alcatel System)

Located in V12, this vacuum system is used primarily for experiments in the vacuum and thin-film classes. The system is flexible and features a basic vacuum system and gauges to which experiments may be attached via one of two NW-40 high-vacuum fittings. The system, as seen in figures 1 through 3 below, consists of:

Turbo Pumping System 2
Figure 1. System Overview

Turbo Pumping System 2
Figure 2. Components of the turbopump system

Summary of Valves in the system:

Turbo Pumping System 2
Figure 3. System Overview - Valve Details

Summary of Gauges in the system:

  • Convectron Gauge
    Convectron Gauge A type of thermocouple gauge, this instrument (a Granville-Philipe type 275) reads manifold pressures up to 800 torr and down to 0.001 torr. This gauge is used to indicate the pump inlet pressure (often zero in operation) and is useful when starting the system to indicate the pressure where the turbo pump may be turned on. WARNING: This gauge is sensitive to the type of gas being measured. For gases other than nitrogen, a conversion chart is required: see the link at the bottom of the page to obtain the PDF for this gauge (see section 6 of the manual). While this gauge is accurate with a single gas (e.g., nitrogen or argon) the gauge is difficult to use in a mixed-gas environment. The primary usage is in system start-up.
  • Ion Gauge
    Ion Gauge This high-vacuum gauge can read pressures below 10-4 torr. The HPS 919 hot cathode controller features a digital readout as well as overpressure protection. This gauge indicates pressures in the gauge section and is useful in determining that pressures are low enough to operate the mass spectrometer. WARNING: Activating the filament at high pressures will cause it to burn-out. Do not turn this gauge on until (a) the main valve is open and (b) the Convectron indicates a pressure below 1 millitorr..

Operation of the system

Connect the experiment (if in use) to one of the NW-40 fittings (i.e. through the MANIFOLD or AUX valves). Usually the fitting off the MANIFOLD valve is used (as shown in the photos on this page).

Turn the main power ON (to power the system gauges - the ones on the left) and turn the mechanical pump ON using the switch on the rear of that pump. The system will begin rough-pumping. Open the MAIN valve and the Convectron will show the current pump inlet pressure. The MANIFOLD valve can also be opened now allowing evacuation of the experiment as well.

Continue monitoring the turbo-pump inlet pressure via the Convectron gauge until a pressure of 1 torr is achieved at which point the turbo-pump may be started using the START switch on the CFV-100 controller. The controller will not allow the pump to start until this point (i.e. if it fails to start, the inlet pressure is not low enough and it will be required to wait longer until the system pressure falls). Pump operation may be verified by the yellow 'underspeed' indicator. The pump will accelerate to 27,000 rpm and Convectron gauge will show a decreasing pressure, eventually reading zero.

At this point, operation of the system is largely determined by the experiment. The Ion gauge may be used by selecting turning the hot cathode gauge controller on, selecting the PRESSURE display function via the front buttons, and switching the filament ON via the toggle switch. If the pressure is too high, the filament may not light, otherwise the filament will be visually observed to lluminate and the gauge will display current pressure. Be sure to limit filament usage and duty cycle to 30 seconds ON, one minute OFF as required.

The mass spectrometer may also be used but to ensure pressures are low enough (i.e. total pressure is below 1 * 10-4 torr), use the ion gauge to verify the pressure FIRST before turning the RGA/Mass Spectrometer on.

Operation of the system - Gauge Experiment

The most common use of this system is for the roughing gauge experiment for vacuum and thin-film laboratories. This experiment consists of four gauges of different technologies on a manifold along with two valves allowing introduction of gases as per figure 4 below:

Turbo Pumping System 2
Figure 4. Gauge Experiment - Valves

Turbo Pumping System 2
Figure 5. Gauge Experiment - Gauges

In order to reduce pressure in the experiment manifold, the MANIFOLD valve may be opened. To introduce gases into the system, needle valves are used along with absolute-sealing toggle valves. Open the toggle valve to admit gas then use the needle valve to regulate the flow of gases into the manifold. Once pressure is at a desired level, the toggle valves should be closed since needle valve are not absolute selaing and so pressure will continue to rise continually.

When the experiment is complete, be sure to turn off gas supplies at the source (i.e. the supply bottle) and be sure the toggle valves are closed.

More details may be found in the experiment itself (on the course home pages)

System Shutdown:

Turn off all gauges, especially the ion gauge if currently on). Close both the MANIFOLD and MAIN valves and turn the turbo pump OFF. Wait until the pump has stopped spinning (about five minutes) then turn the mechanical pump OFF. Shut off the main power.

LINKS:


Updated 2012/01/11 by M. Csele


Copyright (C) Niagara College, Canada, 2012
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