Question

What tool is used to measure gas pressure?

Answer 1

There are different devices which are used to measure gas pressure. Depending upon the intensity of pressure, we can choose a suitable device for measurement. The range varies from very simple devices made from glass tubes to very precise one that are capable of detecting a minute change in pressure.

Complete step by step answer:
Following is the description of few important devices commonly used to measure gas pressure:
Vacuum gauge: It can measure pressure from $50{\text{ mbar}}$ to $1000{\text{ mbar}}$ . Some special and very sensitive types of vacuum gauges can measure pressure down to ${10^{ - 14}}{\text{ bar}}$ .
In this tool a pressure sensing element changes its shape in response to change in pressure. Another element which is connected to the needle moves this reading needle. In this way, we can know the reading represents a particular pressure.
Pressure gauge: It is used to measure high pressure. It can measure pressure from ${\text{1 bar}}$ to $600{\text{ bar}}$ . Its structure and working is similar to a vacuum gauge.
Aneroid barometer: It is used to measure atmospheric pressure. The atmospheric pressure on the earth’s surface varies between $950{\text{ mbar}}$ to $1050{\text{ mbar}}$ . Therefore, this device is also calibrated between these values.
U-tube manometer: Mercury manometers can measure pressure between ${\text{1 mbar}}$ to $1.5{\text{ bar}}$ . Due to high density, usually mercury is used. A relatively small size of tool can be managed to measure the pressure with mercury.
One end of this U-tube is open to the atmosphere and the other end is exposed to the gas. The difference in heights of these two levels can be measured. Then by applying the formula, $p = \Delta h \cdot d \cdot g$ , we can calculate the gas pressure.

Note:
Most gauge equipment measures pressure relative to atmospheric pressure as the zero point. A tool that uses vacuum as zero point measures in absolute scale. Tire pressure and blood pressure are gauge pressures by convention while atmospheric pressure and very low pressure near to vacuum are absolute pressures.