What is a vacuum switch

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What is a vacuum switch?

A vacuum switch is an electronic or mechanical device that provides an electrical switching contact function at a defined vacuum gas pressure level. It’s used in many vacuum applications for pressure control purposes and safety interlock functionality.

A multistage turbomolecular pumping system requires an adequate vacuum pressure level to operate and a vacuum switch can be used to control the pump and protect it from operating at too high pressure.

The fore-line vacuum pump controls the fore-line vacuum pressure required for the turbomolecular pump to operate.  When the fore-line vacuum pressure reaches the predefined switching point, the vacuum switch closes a relay contact that provides an electrical signal to start the turbomolecular pump.

To prevent a vacuum switch from being unstable and provide irregular oscillations as a result of measurement noise or pressure pulsing, two different switch points are normally defined. These are commonly referred to as a setpoint value and a hysteresis value. A typical situation is illustrated at the figure to the right. When the vacuum pressure crosses the setpoint value the vacuum switch relay is energized and the normally open contact closes. It will open again when the hysteresis value is exceeded. The choice of using the normally closed or the normally open contacts depends on the desired state of the contact when the relay is de-energized.

Pirani vacuum switch

In semiconductor manufacturing equipment, wafers are transferred from ambient air pressure to the vacuum processing chamber using a load lock. The vacuum gas pressure in a load-lock chamber requires to be accurately controlled to prevent ambient air and particulate contamination. A combination of pressure- and vacuum switches are typically used to control the pumping and ventilation cycles.

Accurate and repeatable vacuum pressure control and surveillance is critical in many vacuum processes and applications. The industry has moved from mechanical vacuum switches to electronic vacuum switches.

Vacuum setpoint graph

In modern vacuum equipment design, vacuum switches are often an integrated part of the vacuum measurement equipment. A vacuum transducer can have multiple independent mechanical- or solid-state relay switches that are controlled by one or more vacuum pressure sensors. The SmartPirani™ transducer is an example of a wide range vacuum transducer with three independent high-performance solid-state relays with closing and breaking contacts.

Load-lock pressure cycle graph
SmartPirani transducer

SmartPirani™ vacuum transducer with vacuum switch function

■  Record-breaking performance

■  1E-6 to 1200 mbar range

■  Gas independent >2 mbar

■  Set points for control

■  Digital interface

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