Bayard Alpert Gauge (BA Gauge) has been developed by HINDHIVAC to meet the needs of the high vacuum and ultra high vacuum measurements. HINDHIVAC hot cathode ionization gauge is based on Bayard Alpert principle. The cathode is directly surrounded by the ion collector in the form of helix. The anode is used as the outer electrode and shaped like a conventional grid. The gauge function as a normal amplifier where the grid current is a measure of the pressure. The Bayard Alpert Gauge is used to measure vacuum in ultra high vacuum ranges between 10-4 to 2 x 10-10 m.bar. The Bayard Alpert Gauge is provided with display of pressure with auto ranging facility. The gauge also comes with set point controller as a option.
This is a cold cathode ionisation Gauge consisting of two electrodes anode and cathode. A potential difference of about 2.2 KV is applied between anode and cathode through current limiting resistors. A magnetic field is introduced at right angles to the plane of the electrodes by a permanent magnet having nearly 800 gauss magnetic field which will increase the ionisation current.
The electrons emitted from the cathode (gauge head body) of the gauge head are deflected by means of magnetic field applied at right angles to the plane of the electrodes and are made to take helical path before reaching the anode loop. Thus following very long path, the chance of collision with gas molecule is high even at low pressures. The secondary electrons produced by ionisation themselves perform similar oscillations and the rate of ionisation increases rapidly. Eventually, the electrons are captured by the anode and equilibrium is reached when the number of electrons produced per second by ionisation is the sum of positive ion current to the cathode and the electron current to the anode and is used to measure the pressure of the gas.
The Cold Cathode Penning gauge is designed on this detection method to read vacuum from 10-2 to 10-6 m.bar. The vacuum reading efficiency is enhanced by utilizing cross coupled static magnetic and electron fields of the gauge head. The gauge is stabilized to high voltage DC power supply of about 2 KV. The ionization current in terms of vacuum can be noted from the front panel micro-ammeter. All the high voltage points in the penning gauge are well insulated to eliminate any accidental contact by the user.
Change of pressure in vacuum systems brings about a rise or fall in number of gas molecules present and hence a rise (or) fall in the thermal conductivity of the gas. Thus the heat loss of constant voltage electrically heated filament in the system varies with the pressure.
The pirani gauge head filament has high temperature co-efficient of resistance. So a slight change in system pressure brings about useful change in filament resistance resulting in an out of balance voltage which can be read as a pressure on meter. The pirani gauge head indicates the total pressure of combined gases and other vapors in the system on the heated wire, which can loss heat to both gas and vapor molecules. The change in resistance due to temperature build-up, of a coil filament, which is supplied with constant voltage placed in Wheatstone bridge configuration, consequent to the pressure and thermal conductivity which is directly read by the gauge in terms of m.bar.
The gauge consists of the stabilized power supply and the indicating meter with the arrangement to select any of two gauge heads. Each gauge head consists of bridge and calibration elements. These heads are factory calibrated with full interchangeability. Each gauge head is provided with `O' ring coupling, to braze to customer's vacuum system.
Microprocessor based Pirani and Penning Digital Gauge has flexibility with inter changeable modules to have the different combinations of Pirani Gauge Head, Controller, Penning gauge head, and power supply. The digital display has been weighed most important features of this instrument as user friendliness depends on interrogating the key switches with display parameter.
The Microprocessor based Pirani & Penning Digital Gauge instrument will have facility to connect with other equipment or with computer having serial communications port with RS-232C signal levels with programmable baud rate. The microprocessor gauge is provided with main digital display with exponent reading and bar graph. The penning reading can be assigned to main digital display. The pirani can be assigned to bar graph or vice versa. The front panel LED's indicate the sensor No. for which the vacuum reading is displayed.
The microprocessor gauge is provided with a facility of serial communication port RS-232C with signal levels and programmable baud rate. Which can be linked to computer or any system process integration. The microprocessor gauge finds use with vacuum system with complete Automatic operation, Total system Automation with programmable process parameter, also can be hooked to computer.
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