It was in 1643 that the Italian physicist Andrea Torricelli performed the first vacuum experiment. Torricelli was a great mind who studied with the likes of Galileo during the period of great learning known as the Renaissance.
Torricelli was part of a revolution in the scientific method that has impacted scientific thought to this day. Click the link: https://www.encyclopedia.com/people/science-and-technology/physics-biographies/evangelista-torricelli for more information about this scientist and thinker.
Measuring vacuum pressure has come a long way since then. Now it is possible to construct measurements with a high degree of accuracy.
Putting a number on the absence of something is known as vacuum pressure measurement. Vacuum is the negative pressure of a volume of space that occurs when air is absent, relative to the surrounding atmosphere. There are no universal units for vacuum pressure measurement, so different scales and units are required.
There are many types of vacuum pressure measurements, each with their own benefits. Below, you will find several of these methods described.
Negative gauge pressure
When you measure the vacuum pressure, you may notice a difference between the absolute and negative gauge ranges. Although these terms are often used interchangeably, there are significant differences between the two.
When choosing a vacuum measurement instrument, it’s important to understand how negative gauge pressure differs from the absolute range. Negative gauge pressure occurs when the absolute pressure of a vacuum is lower than the atmospheric pressure.
The smallest negative gauge pressure is -14.7 psi. There is a technical explanation for this difference. Negative pressure is a pull. Regardless of the difference in the two terms, they refer to the same phenomenon.
In other words, negative pressure is a negative gauge pressure that occurs when the absolute pressure is lower than the operating pressure. Using this method, you can measure negative pressures of vacuums with an accuracy of ten percent.
Ionization gauges
Ionization gauges are electrochemical devices that measure vacuum pressure using ionization. The ionization process separates electrons in a gas, which are then partially absorbed as ions. These ions are then accelerated towards the anode, where they collide with molecules of the gas.
The emission current is measured in a circuit, where the cathode’s heat output is controlled. The pressure indication increases as the number of ions in the gas increases.
Ionization gauges are sensitive to ionizing radiation, and therefore must be used in environments where the radiation is present. In many cases, the gauge’s resistance may change as a result of this damage.
As such, manufacturers often place the readout electronics inside the gauge head. Nevertheless, in a high radiation environment, it is better to use a gauge with a simple head. However, some gauges do have a shielded version.
Thermocouple
A Thermocouple is a precision instrument used for measuring pressure at very low pressures. Its temperature response depends on the thermal conductivity of the gas in the tube and the surrounding pressure.
In addition to this, the device is susceptible to heat transfer through radiation. To minimize this error, the heated element should be of low emissivity. The range of pressures that thermocouple gauges can measure is tens of mbar to one mbar. This makes it ideal for ranges smaller than Ionization gauges.
The heating and cooling times of the thermocouple are inversely proportional to the pressure. A small electrical charge can be applied to the thermocouple to make it hotter or colder.
A moving coil then measures the output voltage, which is directly proportional to the pressure of the surrounding gas. This method is a cost-effective way of measurement vacuum pressure and can be used in many different circumstances. In this way, the sensitivity of a thermocouple can be increased significantly.
Pirani gauge
A Pirani gauge for vacuum pressure measurement uses the thermal conductivity of gases to measure pressure. It operates at pressures of between 10 and 100 hPa.
The temperature of the heated component, usually a thin film membrane, is brought to an elevated temperature by a bridge circuit. The amount of heat that is transferred from the wire to the surrounding gas depends on its temperature and pressure. As a result, the temperature of the heated component is directly proportional to the pressure.
The principle of operation of a Pirani gauge is similar to thermocouple gauges, except that the wire filament is heated with constant current instead of by a heat source.
However, a Pirani gauge’s response time is much faster than a thermocouple-based gauge. This is because the resistance of a wire is temperature-dependent, and the current flowing through it is proportional to the change in temperature. In addition, modern gauges can measure pressures in the range of 100/10 to 10-4 mbar. Click here for more information about the Pirani gauge.
Each of these methods can offer vital and robust information.
