IGM401 Hornet™ Hot Cathode



IGM401 Hornet is InstruTech’s miniature hot cathode Bayard-Alpert ionization vacuum gauge module with a built-in controller and display.  The pressure measurement range of the IGM401 is 1.00E-09 to 5.00E-02 Torr.

IGM401 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
  • Built-in controller with bright OLED digital display
  • User programmable display units in Torr, mbar or Pa
  • Auto-Ranging of emission current provides optimal and stabile pressure readings over the entire measurement range from low to high vacuum
  • 1 analog output and 1 setpoint relay
  • RS485 serial communications
  • Also a lower cost, plug-compatible direct drop-in replacement for the Granville-Phillips® 354 and 355 Micro-Ion®
  • CE and RoHS compliant
  • Standard warranty of 18 months

Optional Power Supply 

Check out our power supply PS501


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 IGM401?

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

Why is the IGM401 referred to as a “Module”?

A module is a complete vacuum gauge which combines the sensor and electronics (controller) in one assembly requiring no external controller to operate. The IGM401 is a vacuum gauge module with a built-in controller, display and it also provides process control signals.

What is the power requirement of the IGM401?

20 to 28 Vdc, 13 W. Users can provide their own power supply or use InstruTech’s optional power supply PS501-A.

Load more

Trademark Acknowledgements listed in the IGM401 Data sheet.