Capacitance manometers are a type of electro-mechanical gauge that are the ideal choice when measuring both pressure and vacuum. The MKS Baratron capacitance manometers measure true pressure and they are insensitive to the type of gas being measured. The Baratron capacitance manometers are known for being highly accurate and reliable, along with having an easy interface compared to other vacuum gauges. This is due to not only their performance, but their overall structure.
PARTS OF A CAPACITANCE MANOMETER AND HOW THEY WORK
– translates the pressure movement in the diaphragm into an electrical signal equal to pressure.
– the diaphragm exposed to the pressure or vacuum being measure by an inlet tube.
– usually a ceramic disk mounted in the reference cavity behind the diaphragm. Contains conductive pathways and is powered by an electrical signal.
When the pressure differences between the process and the reference cavity deflect the diaphragm, the distance changes between the diaphragm and the electrode. Variations in the distance cause variations in the capacitance between the diaphragm and the electrode. These variations are equivalent to pressure change. Because these differences are produced by physical changes within the gauge and not by changes in the properties of gas, pressure measurements are considered insensitive to the gas being measured.
TYPES OF CAPACITANCE MANOMETERS
ABSOLUTE CAPACITANCE MANOMETER
The changes in pressure are determined by measuring the change in the sensor’s diaphragm and an electrode.
DIFFERENTIAL CAPACITANCE MANOMETER
Differential Capacitance Manometers: read the difference in pressure between the inlet tub and the reference cavity behind the electrode.
BARATRON CAPACITANCE MANOMETER STRUCTURE
MKS manufactures the Baratron capacitance manometers with exclusive nickel-based alloys such as Inconel and Incoloy. These materials make the instruments resistant to corrosion. They are also constructed to assure overall operator safety. MKS’ manometer sensors are fully welded and are guaranteed to be 100% leak-check before assembly. This ensures that process gases are completely contained within the sensor in case of diaphragm failure. There are no other pressure or vacuum gauges that can ensure and offer this level of user safety.
OTHER TYPES OF VACUUM GAUGES
MECHANICAL VACUUM GAUGES
Mechanical gauges operate by using a mechanical or diaphragm arrangement. The arrangement controls the gauge without any electronics and physically moves the indicator needle to show the measurement of pressure or vacuum.
THERMAL VACUUM GAUGES
Thermal gauges, also known as Pirani, thermocouple and convection gauges, operate based on the principle of thermal conductivity. These gauges use an electrically heated wire to determine the measurement of pressure. The measurement is based upon the rate of the head losted from the wire and its variation with the thermal conductivity of the gas. The variation in this measurement requires a change in the circuits electrical current, voltage or power – the change is what is recorded as pressure/vacuum.
These gauges are used with positive-pressure applications. Strain-based gauges utilize a diaphragm with a strain-sensing electronic circuit. When a change in pressure occurs, the diaphragm deflects causing a strain.
IONIZATION VACUUM GAUGES
These vacuum gauges, also know as the hot-filament gauge, rely on the ionization of ambient gas molecules and measurement of the ion current. The ion current and the vacuum pressure are parallel in the chamber.