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The test cartridge must be inserted into the chamber in such a way that the hole in the test cartridge case lines up with a gas port hole that channels the gas pressure from the cartridge case to the face of the sensor. The measurement accuracy of the pressure measurements with 21st century high-pressure sensors is expected to be ≤ 2%. [7]
A heated metal wire (sensor wire, or simply sensor) suspended in a gas will lose heat to the gas as its molecules collide with the wire and remove heat. If the gas pressure is reduced, the number of molecules present will fall proportionately and the wire will lose heat more slowly. Measuring the heat loss is an indirect indication of pressure.
The low-pressure sensitivity of hot-cathode gauges is limited by the photoelectric effect. Electrons hitting the grid produce X-rays that produce photoelectric noise in the ion collector. This limits the range of older hot-cathode gauges to 10 −8 Torr and the Bayard–Alpert gauges to about 10 −10 Torr. Additional wires at cathode potential ...
This schematic shows the component parts of a typical leak-down tester. The gauge on the right is held at a standard pressure by adjusting the pressure regulator while the gauge on the left shows an example reading of 85, or 15% leakage. A leak-down tester [2] is essentially a miniature flow meter similar in concept to an air flow bench. The ...
The inlet pressure gauge will indicate this pressure. The gas then passes through the normally open pressure control valve orifice and the downstream pressure rises until the valve actuating diaphragm is deflected sufficiently to close the valve, preventing any more gas from entering the low pressure side until the pressure drops again.
For low pressure differences, light oil or water are commonly used (the latter giving rise to units of measurement such as inches water gauge and millimetres H 2 O). Liquid-column pressure gauges have a highly linear calibration. They have poor dynamic response because the fluid in the column may react slowly to a pressure change.
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All mass flow controllers have an inlet port, an outlet port, a mass flow sensor and a proportional control valve. The MFC is fitted with a closed loop control system which is given an input signal by the operator (or an external circuit/computer) that it compares to the value from the mass flow sensor and adjusts the proportional valve ...