IGM400 Hornet™ Hot Cathode



The IGM400 Hornet is a hot cathode Bayard-Alpert ionization vacuum gauge module designed to work specifically with InstruTech’s B-RAX 3200 vacuum gauge controller. All display and control functions are performed remotely by the B-RAX 3200 or the FlexRax controller.

The pressure measurement range of the IGM400 is 1.00E-09 to 5.00E-02 Torr.

IGM400 is available with various fittings including NW16KF, NW25KF, NW40KF, 1 1/3 in. Mini-Conflat, 2 3/4 in. Conflat, 3/4 in. O.D. Tube (O-ring compression) and 1/2 in. Cajon 8VCR female.


  • Wide measurement range of 1.00E-09 to 5.00E-02 Torr
  • CE and RoHS compliant
  • Standard warranty of 18 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 IGM400?

  • 1.00E-09 to 5.00E-02 Torr
  • 1.30E-09 to 6.70E-02 mbar
  • 1.30E-07 to 6.7 Pa

Do I need a controller to operate the IGM400?

Yes. The IGM400 is not a functional device without the InstruTech B-RAX or the FlexRax controller.

Can I use a controller other than the InstruTech B-RAX or FlexRax controller to operate the IGM400?

No. The IGM400 is only functional when used with the InstruTech B-RAX or the FlexRax controller.

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