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Ion Gauges


  • Bayard Alpert Gauge
  • Nude Head
  • Conflat ® Flange
  • Low X-Ray Limit to 3 x 10-11 mbar
  • High Reliability
  • Long Life
  • Robust, Efficient Design
  • Twin Filaments: Tungsten, Thoria-coated iridium or Yttria coated iridium.




SS Scientific supply a new, improved Bayard Alpert ionisation gauge specifically designed for long life and reliability.

As well as using high specification materials, the surface area of the grid structure has been reduced, and the collector plus collector shield are of an improved design. Compared to standard BA gauges, these improvements mean that the SSIG17/18/19 has a lower x-ray limit that enables pressure measurement down to 3 x 10-11mbar.

At higher pressure operation (up to 102 mbar), the rugged, robust characteristics of the gauge construction ensure a long-life of reliable, repeatable pressure measurement.

Whatever the application, the very competitive price of the SSIG-17/18/19 ion gauge make it a must for all vacuum systems.

Principle of operation

A hot cathode ionisation gauge comprises three electrodes: a filament, grid and collector. Electrons are produced from the filament by thermionic emission. A positive potential on the grid attracts the electrons away from the filament, causing them to oscillate through the fine structure many times, until eventually they collide with the grid. Alternatively, the electrons collide with gas molecules producing a positively charged ion, which are collected at a negative electrode (Collector) at the centre of the grid structure. The current depends upon the number of ions which is directly proportional to the pressure in the gauge.

X-ray Limit

The low pressure limit of the gauge is restricted by the ‘x-ray limit’. Electrons hitting the grid produce soft x-rays which in turn produce photoelectron emission (‘photoelectric noise’) from the collector. Since the measurement electronics cannot distinguish between collecting a positive ion or losing a photoelectron, a theoretical minimum detectable pressure is set. The effect is small and it kept to a minimum by careful design of the gauge.

Gauge Leads

To connect a SSIG-17/18/19 ion gauge head to a controller, a lead is required. Bakeable leads are available for all three gauges, which means that the gauge can be operated (and pressure monitored) whilst the system is being baked. Also, the gauge heads can be degassed whilst the system remains hot.

The standard lead is 3 meters long but any length can be supplied to order.

Gauge Calibration

Ionisation gauges have different sensitivities for different gases and are usually calibrated for nitrogen. Many users accept the inaccurate  pressure measurement for a gas mixture and rely on the long-term reproducibility of the gauge.

For accurate pressure measurements the gauge head should be calibrated for the gas species being measured.


Flange 70mm OD 70mm OD 70mm OD
Pressure range (mbar) 10-2 to 3 x 10-11 10-2 to 3 x 10-11 10-2 to 3 x 10-11
Degas Power (W) 40 to 100 40 to 100 40 to 100
X-ray limit (mbar) 3 x 10-11 3 x 10-11 3 x 10-11
Sensitivity (mbar-1) 19 19 19
Filament (replaceable) Twin tungsten Twin Thoria coated iridium Twin Yttria coated iridium

 Vacuum Controller PVCX



  • Pressure measurement 1000 mbar to <10-11 mbar
  • High accuracy, high stability and low noise
  • Built in ion gauge and Pirani gauge. Optional third gauge. Gauge head naming for identification
  • Built-in thermocouple for multi-step bake-out. Optional second thermocouple for dual-zone control
  • 7 Trips, 2 Digital inputs
  • User-definable analogue output
  • RS232/485 interfaces. Full computer control via MODBUS or (ASCII-based) QueBUS multi-parameter messages. USB/Ethernet option.
  • Free VacTools software for data logging, graphical display and control.



Ion Gauge: 1x UHV, dual Iridium-based filament. Yttria or Thoria-coated filaments.
Filament Drive: High stability, low noise, constant current dc.
Filament Drive Rating: 0-5A (8V compliance)
Emission Control: PID control with emission measurement for accurate pressure correction
Manual Emission: OFF, 0.05, 0.1, 0.15, 0.25, 0.4, 0.6, 1, 1.5, 2.5, 4, 6, 10mA
Auto-emission: Emission automatically optimized for measured pressure
Emission features: Soft-start and Ultra soft-start (new filament) options. User-definable min & max emission
Degas Type: Thermal/Electron bombardment
Degas: Ramped to user selectable low/mid/high power
Degas Features: User-defined ramp/soak periods. User-defined pressure suspend to allow vacuum recovery.
Degas Pressure: Displayed during degas
Degas on/off: No interruption of ion gauge operation during degas start/stop transitions
Degas trip monitoring: Continuous trip monitoring during degas with no interruption
Electrometer: Range: <1e-12 to 1e-2. High stability
Gauge Sensitivity: 1.0 to 99.9 (resolution 0.1)
Gas Sensitivity: 0.01 to 99.99 (relative to Nitrogen = 1.00
Pump-down: User-defined auto pump-down: backing gauge dependent ion gauge start-up pressure; trip allocation for external events (valves…), delay time, restart time etc…
Built in: Support for VSP521/VSP841 as standard (user selectable)
Module supported: 1 module
Module options: “V”: VG Pirani. “E”: VSP521. “F”: VSP841″U” and “W”: Universal linearised output (e.g. other gauge controllers, mini-convectron, Stinger…) User configurable voltage-pressure relationship.”K”: Type K thermocouple input module for dual zone bake-out control
Bake-out: Single zone or Dual-zone. Can be run together or separately
Built in: Type K thermocouple. Standard mini-thermocouple connector
Option: Addition of “K” module for dual zone control
Range: Room temperature to 500°C. Precision CJC. Reproducibility <±0.5°C. Absolute <±2°C (can be user calibrated)
Bake-out Functions: 6x ramp/soak steps, each up to 99.9 hours duration (0.1 hour resolution). Individual trip allocation for power switching (e.g. 3 trips for 3Φ).User-defined pressure and digital input interlocking (ramp suspend/time suspend/abort).User-defined temperature hysteresis.Auto-degas at end of bake-out.
Trips: 7 (4x SPCO relays 1A@24Vdc/ 0.5A@40Vac + 3x NPN open collector 250mA/12Vdc)
Trip assignments: Individually assignable: external interlock to any ion or backing gauge, ion gauge status (on, off, degas), bake-out power switching, pump down external drive…
Digital Inputs: 2x opto-isolated inputs. 3-30Vdc; 2.4kΩ input resistance.
Digital Input assignment: External interlock as trip for ion gauge; control over ion gauge on/off and degas either via input state or toggle state; bake-out trip; pump-down trip; backing gauge/pump operation…
Interlock Response times: 0.2 sec max. Typically <0.1sec
Output: Full scale range: -0.2V to 10.2V (12 bit resolution). User-definable pressure/voltage relationship
Accuracy: Precision reference-based:  <±0.2%.
Assignment: User configurable: Ion gauge (emission and sensitivity corrected), any secondary gauge, gauge combinations, bake-out temperature…
Functionality: User-defined voltage range, assigned pressure/temperature range, lin or log relationship…
Dimensions: 19″ rack mounting: WxHxD: 484x44x260mm (19”x1.73”x10.25”) + 50mm for connectors
Weight: 5.6kg
Electrical: 115/230Vac. 8W (gauge off), Max: 60W (full degas)
Display Type: Dual OLED display:Left: 100×16 pixel graphical display.Right: 2 line x 16 character display.High brightness. High contrast. Long life >100,000h to half-brightness
Display Modes: User-configurable Gauge positioning between Primary and secondary displaysDisplay “screen saving” mode”Quiet” mode option removes unused/disconnected gauges/thermocouple
Display Resolution: Ion gauge: Pressure: 1 or 2 decimal place resolution. Ion current: auto-ranging 4 significant figures. Secondary gauges: 1 decimal place resolution. Temperature: <0.1°C measurement resolution, 0.1°C display resolution.
Manual input: Intuitive menu-driven via 5 front panel touch buttons
Communications: Multi-drop RS232 (up to 8 units (port dependent)) and RS485-3 wire (up to 16 units). MODBUS protocol. Simultaneous multiple parameter read/write; floating point resolution.QueBUS protocol. ASCII-based protocol with multiple parameter read/write
Communications connection: 2x RJ45 for simple daisy-chaining



  • Free control, monitoring and data logging vacuum system software
  • Windows 7 and above. (XP version available)
  • Unlimited serial interfacing with unlimited PVC/system count
  • Full control over PVC
  • Continuous monitoring and data logging for user-selected parameters
  • Graphical data presentation
  • Print out data export
  • Data exchange interface for third party software to access data
  • Range of hardware options available (serial, USB…) with cabling


Ion Gauge Head Refurbishment




  • Ion Gauge Heads
  • Filaments



  • Leak Test
  • UHV Compatible



SS Scientific have the capability to refurbish ion gauge heads to an ‘as new’ performance guarantee. It is a cost effective way to extend the lifetime of your equipment.

Our wealth of experience in manufacturing techniques used to produce these items is your guarantee of unbeatable quality and our many years of experience in vacuum technology ensures the high quality needed for UHV applications. We also supply exchange gauge heads to reduce down-time of your vacuum equipment.

We will rebuild, clean and leak check your gauge head. The refurbishment includes new filaments (tungsten as standard) and where necessary grid, collector and barrel connectors.

We specialise in the refurbishment of the VG VIG series of gauge heads, but would be pleased to quote for any other manufacturers head.