INFICON CATALOG 2000-2001 - Schoonover, Inc.

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Vacuum Gauges Transmitter Technology Hot Cathode Ionization Vacuum Gauges In a hot cathode ionization gauge, the electrons emitted from the surface of a hot filament are attracted to a highly transparent grid made from very thin wire and at a positive electrical potential. With the grid so open, there is a very high probability that the electron will pass right through the grid and not strike a wire. If the grid is surrounded by a screen at a negative electrical potential, the electron will be repelled by this screen and be attracted back to the grid. This process can happen many times before the electron finally hits the grid and is lost. As a result, very long electron paths can be achieved in a small volume, increasing the probability of ionizing a gas molecule. The resulting ions are attracted directly to the collector. Most hot cathode sensors used are based on this Bayard-Alpert arrangement of electrodes. With this electrode arrangement it is possible to make measurements in the pressure range from 10 -10 to 10 -2 mbar (Torr). Other electrode arrangements permit access to a higher range of pressures from 10 -10 mbar (Torr) up to 10 -1 mbar (Torr). For measurement of pressures below 10 -10 mbar (Torr), extractor ionization sensors are employed. In extractor ionization gauges, ions are focused on a very thin and short ion detector. Due to the geometry of this system, interfering influences such as X-ray effects and ion desorption are almost completely eliminated. The extractor ionization gauge permits pressure measurements in the range from 10 -12 to 10 -4 mbar (Torr). INFICON improvements in electrode arrangements provide a wider measurement range combined with excellent repeatability. The Bayard- Alpert Pirani Combination Gauge further improves the measurement range in an easy to use package. Cold Cathode Ionization Vacuum Gauges (Penning) The cold cathode ionization gauge dispenses with the hot filament and uses a combination of electric and magnetic fields. If one applies a potential of a few kilovolts between a parallel plate capacitor in the presence of a gas pressure of a few mbar (Torr), a glow discharge will result. In the glow discharge, energetic free electrons interact with neutral molecules to produce ions and more free electrons. The ions are attracted to the negative electrode and when they strike it, secondary electrons are created, which are attracted to the positive electrode. The glow discharge continues as long as the number of electrons being created is equal to or greater than the number being removed at the positive electrode. Transmitter Technology Transmitters convert an analog input signal (pressure) measurement value into an analog normed electronic measurement signal, i.e. 0 Ð 10 V. This measurement signal is typically available as a linear or logarithmic output signal. The advantages of transmitters over conventional gauges with a separate signal processing device are: ♦ Sensor and electronics in one compact package ♦ Large cost savings ♦ Direct connection to customer control units ♦ A simple formula to convert the measurement signal into any desired pressure unit ♦ Clear error messages can be transmitted because of the structured measurement signals ♦ Digital interfaces (RS 232 C, Profibus, DeviceNetª) allow direct measurement readings in digital form ♦ Integrated setpoint for direct process control based on pressure measurement ♦ Measurement signals can be transmitted over greater distances The INFICON transmitter vacuum gauge line provides unparalleled performance for system manufacturers taking advantage of unique technologies combined with cost saving potential. The transmitter technology combines the sensor with the control and evaluation electronics in one compact package. Several output concepts like 0 Ð 10 V analog output, digital RS 232 C and fieldbus communications are available. INFICON transmitter technology reduces the costs for vacuum measurement and system integration to a minimum. The Penning gauge design employs a ring as the positive electrode (anode), which is centrally located between two electrically connected, negatively charged, parallel plates (cathodes). Electrons are attracted to the plane of the ring. Upon arrival, these electrons pass through the ring, and continue to oscillate between the two cathode plates. This configuration lowers the pressure at which a discharge can be sustained by increasing the electron path length. By introducing a magnetic field this electron path becomes a spiral, significantly increasing the path length. This further lowers the pressure at which the discharge can be maintained. INFICON design concepts permit safe and reliable operation of ÒPenningÓ sensors in the pressure range from 1á10 -9 mbar to 1á10 -2 mbar (Torr). B6.4
Transmitter Technology Vacuum Gauges Conventional Measurement Systems Conventional vacuum measurement systems consist of separate sensors and control units. The unconditioned sensor signal has to be transmitted to the control and evaluation unit which makes the system susceptible to interferences and therefore requires special shielded cabling. Integration into vacuum systems is space consuming and usually inconvenient since the controller outputs are not linear or described completely by one simple formula and therefore require look-up tables to be integrated into the software. Transmitter Based Measurement Systems Analog Technology Digital Technology Digital interfaces (RS 232 C, Profibus DP, DeviceNetª) allow direct measurement readings in digital form and further enhance the advantages of transmitter technology. INFICON digital transmitters provide control of processes from one control position. This allows communication of exact digital information, independent control, maintenance and diagnostic routines for each connected instrument and simplifies the connection diagram further. Measures of control include: monitoring of measurement values, the automatic zero point adjustment of gauges, reminding the operator of scheduled maintenance work, warning signals in case of instrument failure and more. INFICON digital transmitters offer the flexibility and control of network communications further enhancing system quality and efficiency. B6 The combination of sensor and electronics in one package simplifies the connection scheme of vacuum systems and saves valuable space and costs. The measuring signal is converted into an analog 0 Ð 10 V output signal, which can be directly converted to a digital signal and evaluated by a PLC or other control. This eliminates the need for a separate control and display unit. No look-up table is required anymore since the analog output signal is described completely by one simple formula. INFICON analog transmitters are the most economic solution for advanced vacuum measurement. B6.5
Page 1 and 2: B6 Vacuum Gauges Vacuum Gauges and
Page 3: Basic Terms of Vacuum Metrology Vac
Page 7 and 8: SKY TM Capacitance Diaphragm Gauge
Page 13 and 14: Bayard-Alpert Pirani Gauge BPG400 V
Page 15 and 16: Pirani Standard Gauge Vacuum Gauges
Page 17 and 18: Pirani Standard Gauge Vacuum Gauges
Page 19 and 20: Bayard-Alpert Gauge Vacuum Gauges B
Page 21 and 22: Bayard-Alpert Gauge Vacuum Gauges T
Page 23 and 24: Penning Gauge PEG100 Vacuum Gauges
Page 25 and 26: Vacuum Gauge Controller VGC103 Vacu
Page 27 and 28: Vacuum Switch VSA100 Vacuum Gauges

INFICON CATALOG 2000-2001 - Schoonover, Inc.

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