The document discusses different types of vacuum gauges: - Ionization gauges measure pressure down to 2 torr by ionizing gas with electrons and measuring the current. - Pirani gauges use thermal conductivity to measure pressures from 1 Torr to 1 milliTorr and are rugged, inexpensive, and provide accurate responses. - Thermocouple gauges measure the temperature of a heated wire in contact with a thermocouple as an indicator of pressure for different gases.

1. GAUGES

2. Ionization Gauge
• It can be used to measure pressure down to about 2 torr.
• The gas is ionized with a beam of electrons and the curr
ent is measured between two electrodes in the gas.
• The current is proportional to the number of ions per unit
volume, which also proportional to the gas pressure.

3. Pirani Gauge
• The Pirani gauge is a robust thermal conductivity gauge used for the measu
rement of the pressures in vacuum systems.
• The thermocouple (or T/C) gauge is one of the more common and cost effe
ctive gauges for vacuum pressure measurement in the 1 Torr to 1 milliTorr r
ange

4. Applications of Pirani gauge
•Used to measure low vacuum and ultra high vacuum pr
essures.
Advantages of Pirani gauge
•They are rugged and inexpensive
•Give accurate results
•Good response to pressure changes.
Limitations of Pirani gauge
•Pirani gauge must be checked frequently.
•Pirani gauge must be calibrated from different gases.
•Electric power is a must for its operation.

5. Thermocouple Vacuum Gauge
• A Thermocouple is kept in contact with the heate
d wire and the temperature of the wire is directly
measured as a measure of pressure.
• For different pressures, the temperature is mea
sured by the fine-wire thermocouple, the hating
current being initially fixed by the resistance as s
hown in the figure. This device is usually used fo
r comparison purposes. The sensitivity of such a
n instrument depends on the pressure and the w
ire current.

7. McLeod Gauge
• It compresses the low pressure gas so that the increased pressure can be m
easured.
• The change in volume and pressure can then be used to calculate the origin
al gas pressure, providing that the gas not condensed.