BA601/BA602/BA603 Nude and Glass Hot Cathode



These gauges are InstruTech’s classic size nude and glass-enclosed resistive degas (I2R) or UHV EB-degas Bayard-Alpert (B-A) hot cathode ionization vacuum gauges with no onboard electronics. These hot cathode ionization gauges require an external controller such as InstruTech’s B-RAX™ 3300 and B-RAX™ 3400 to operate. They may also be operated using other brands of vacuum gauge controllers capable of running nude or glass B-A gauges.


  • BA601: Measurement range of 2.00E-11 to 1.00E-03 Torr BA602/603: Measurement range of 4.00E-10 to 1.00E-03 Torr
  • Single/dual yttria coated iridium or tungsten filaments
  • Wide range of emission currents (100 μA to 10 mA)
  • BA601/BA602 are available with 2 3/4 in. Conflat® fitting
  • BA603 is available with fittings- NW25KF, NW40KF, 1 1/3 in. Mini-Conflat®, 2 3/4 in. Conflat®, 3/4 in. and 1 in. Kovar and glass port
  • Standard warranty of 12 months


What is the principle of operation?

The hot cathode Bayard-Alpert ionization vacuum gauge operates by ionizing the gas inside the gauge and then measuring the number of ions generated. The ions are then collected giving a measurement of the density or pressure of the gas inside the transducer. The various electrodes used in the transducer design are a collector surrounded by a circular grid with one or two filaments outside the grid.

An electric current is passed through the filament to cause the filament temperature to increase. As the filament temperature is increased, electrons are emitted from the filament surface. The bias voltage between the filament and the grid will accelerate the electrons toward the grid. Most electrons will pass through the grid volume and exit the other side of the grid and then be drawn back into the grid for another traversal through the grid volume. Eventually, most electrons will impact the grid surface generating a current between the filament and the grid which is referred to as the emission current. The electronic controller is designed to maintain a constant, selectable emission current which is independent of pressure. While an electron is traversing inside the grid volume, it may collide with a gas molecule and ionize it which removes an electron. The ionized gas molecule, which now has a positive charge because it is missing an electron, will be attracted to the collector which is at ground potential. A current will be generated by the flow of ions to the collector which is known as the ion or collector current. An electrometer will measure the small ion current generated and a pressure, which is proportional to the ion current, can be calculated.

What is the measurement range of the BA600 series sensors?

  • BA601: 2.00E-11 to 1.00E-03 Torr
  • BA602: 2.00E-10 to 1.00E-03 Torr
  • BA603: 2.00E-10 to 1.00E-03 Torr

Do the BA600 series sensors require an external controller to operate?

Yes. These are standalone sensors requiring a vacuum gauge controller to operate.

Which InstruTech controllers can operate the BA600 series sensors?

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Trademark Acknowledgements listed in the BA600 series Data sheets.