In any vacuum system it is most important to know accurately the level of vacuum on real time basis as even a minor change in vacuum can result in process parameters going haywire and product quality getting adversely affected. In modern day vacuum systems we use sophisticated vacuum gauges to know the vacuum accurately.
In this blog post various kinds of vacuum gauges have been described. Limitations and advantages of these gauges have also been brought out so that engineers using vacuum can select appropriate gauge for the application. Various practical aspects about use of vacuum gauges have also been detailed in this blog post.
U Tube Manometer: – This is the most basic vacuum gauge where height of liquid column of mercury is used to measure vacuum.
- Advantage– It is very simple, inexpensive and independent of system gas.
- Disadvantage– this gauge can measure vacuum only up to 1 Torr.
Bourdon Gauge:- Quite effective for measuring low vacuum, this gauge uses a curved metal tube which is closed on one side and connected to vacuum on other side. Depending on the vacuum level the tube called Bourdon Tube distorts. This distortion is amplified by gears and levers and this indicates vacuum level on the gauge dial.
- Advantage– It is a simple and effective gauge which is quite sensitive.
- Disadvantage– This gauge is dependent on gas in the system and cannot measure high vacuum.
Thermocouple Gauge:- This gauge is very similar to Pirani Gauge except that in a thermocouple gauge a thermocouple is spot welded directly to heated wire so a direct temperature measurement is taken which is converted into measurement of vacuum.
Penning Gauge:- This gauge is named after its inventor. In this gauge, current produced by glow discharge is used to measure vacuum. A high potential difference is applied to produce a self-sustaining glow. Around the glow a magnetic field is applied. The current produced is dependent on the vacuum level and therefore measurement of glow current indicates vacuum level.
- Advantage– It can measure vacuum up to 10-6 Torr accurately.
- Disadvantage– This gauge cannot measure vacuum till vacuum is at least 10-3 Torr since glow cannot be sustained below this vacuum.
Hot Cathode Ionization Gauge:- This is also called an Ion Gauge. In this gauge a hot wire is used to produce electrons by thermionic emission. The electrons thus produced are attracted to anode which is in the form a grid. The Ion current obviously will depend on the vacuum level. Measurement of the current therefore indicates level of vacuum.