What is SRG - Spinning Rotor Gauge Technology?

SRG, spinning rotor gauge, is a measurement technology used in high vacuum measurements. This type of gauge (usually a sphere) works by being suspended in a magnetic field. As the rotor spins rapidly in low vacuum, it collides with gas molecules. As the vacuum level increases, that is, as the gas molecule density decreases, the frequency of these collisions decreases and the rotational speed of the rotor increases.

The measurement determines the gas density by the braking effect of gas friction on the rotor. It consists of 3 parts acting as measuring head, control/reading unit and pressure sensor.

The measuring head contains the magnet and coil system and temperature sensor required for the sensor ball levitation, oscillation damping, acceleration and velocity sensing. One end of the measuring tube is closed, while the other end is welded or flanged. Therefore, the measuring tube is part of the vacuumed medium.

There is no need for any mechanical or electrical transition outside the sensor. For measurement, the SRG measuring head is pushed onto the measuring tube. It is adjusted and fixed vertically with the integrated spirit level. During measurement, the sensor ball is ventilated by the magnetic field and rotates freely with negligible friction. The sensor ball is accelerated to more than 600rpm and then allowed to spin on its own. The sensor is subject to drag caused by the tangential momentum transfer of gas molecules inside the measuring tube.

The unit never needs recalibration as possible aging of the electronic circuits does not affect the repeatability of the measurement readings. It is accurate for most gas types because a measurement is performed based on the density of the gas, not the type.

Provided by PH Instruments products can be viewed here, contact for order.