Vacuum Residual Gas Analysers

Choose first by mass range, then by control and process-integration requirements. The RGA100 family covers 1–100, 1–200 or 1–300 amu and communicates through RS-232C, with Ethernet available through an external adapter. The RGA120 family covers 1–120, 1–220 or 1–320 amu and adds USB, built-in 10/100 Ethernet, analogue I/O, relay, GPIO, Pt100 RTD and trigger connections. It also supports automatic peak tuning and analogue scans up to 260.4 amu/s at 10 points per amu. For new automated equipment, the RGA120 provides the broader integration set, while the RGA100 remains suitable where its mass range and serial-control architecture match an existing design.

Specify the electron multiplier when target partial pressures fall below the practical range of the standard Faraday cup or when low-level measurements require shorter acquisition times. The Faraday cup has a minimum detectable partial pressure of 5 × 10⁻¹¹ Torr, while the multiplier extends this to 5 × 10⁻¹⁴ Torr under the stated nitrogen measurement conditions. The applicable chamber-pressure range also differs: the Faraday cup can operate from 10⁻⁴ Torr towards UHV, whereas multiplier operation begins at 10⁻⁶ Torr. Total-pressure measurement is associated with Faraday cup ion-current measurements. Designs using the multiplier should therefore include suitable pressure interlocking, gain calibration and a method of reverting to the Faraday cup when chamber pressure rises.

The probe mounts on a 2.75 in CF flange and requires a vacuum port with a minimum internal diameter of 1.375 in. Probe insertion is 2.0 in, the distance from the flange face to the top of the ioniser is 8.75 in, and approximately 2.5 in of chamber clearance is required around the exposed ioniser region. The electronics control unit measures 9.1 × 4.1 × 3.1 in and can be separated from the probe before bakeout. The probe can withstand up to 300 °C without the control unit, although 200 °C is the recommended bakeout temperature with the compatible heater jacket. Normal operation is limited to 70 °C, so installation planning should account for process heat, ventilation and service access.

The RGA120 series provides the connections needed for direct interaction with many process-control systems. Its analogue output can be configured for 0–20 V or 4–20 mA and linked to variables such as total pressure, mass ion current, temperature or emission current. The analogue input accepts 0–10 V, 4–20 mA or 4–20 mA with loop power, while the DPDT relay is rated up to 60 W, 75 VA, 125 VDC, 150 VAC or 2 A. A 0–3.3 V GPIO, trigger input and Pt100 RTD input are also included. The RGA100 series instead relies on RS-232C commands, with network control possible through the external Ethernet adapter, so additional control hardware may be required for direct PLC integration.

Quantitative work requires gas-specific sensitivity factors and suitable fragmentation data rather than relying only on a library spectrum. A pure calibration gas is normally introduced at a known pressure, typically around 10⁻⁶ Torr, and its principal mass peak is measured using the Faraday cup. The sensitivity factor is calculated from the change in ion-current peak height divided by the corresponding change in partial pressure. Electron energy, ion energy, emission current, peak width, detector type and other operating settings must remain consistent between calibration and subsequent measurements. If the electron multiplier is used, its gain should be treated as a separate correction factor so that changes in multiplier gain are not mistaken for changes in the intrinsic sensitivity of the analyser head.

The resolution specification means that peaks separated by one nominal atomic mass unit can normally be distinguished when the instrument is correctly tuned. It is defined at 10% of peak height in accordance with AVS Standard 2.3, and the peak width can be held constant across the selected mass range. This is appropriate for identifying many common vacuum species and their fragments, including hydrogen, water, nitrogen, oxygen, argon and carbon dioxide. It does not separate different species that produce ions at exactly the same mass-to-charge ratio, such as nitrogen and carbon monoxide at mass 28. Those cases must be resolved by examining additional fragment peaks, isotopic ratios, process history and calibrated fragmentation patterns.

Both series use a dual thoriated-iridium filament with firmware-based protection and field-replaceable construction. The RGA100 monitors for overpressure at 675 Hz during operation, while the RGA120 checks process pressure before enabling the filament and reports pressure-related errors through its status system. A programmable degas function applies a controlled power ramp of 1–10 W on the RGA100 series or 1–8 W on the RGA120 series to reduce contamination associated with the ion source. The electronics control unit should be removed before high-temperature probe bakeout or probe servicing. Maintenance must use clean vacuum procedures because fingerprints, dust, unsuitable tools or contaminated replacement parts can raise background signals and compromise subsequent gas analysis.

The supplied Windows applications support analogue spectra, histogram scans, pressure-versus-time monitoring, leak testing and scheduled acquisition. Results can be displayed using linear or logarithmic scales and pressure units including Torr, bar and pascal, while alarms and gas labels can be configured for monitored species. Data can be exported in CSV format, and plots can be saved in common image and document formats for analysis or reporting. Multiple analyser heads can run concurrently through separate software instances, subject to the host computer’s available resources. For automated systems, the RGA120 supports SCPI control through USB, Ethernet or RS-232C, while the RGA100 uses its serial high-level command set and can be networked through the external Ethernet adapter.