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A vacuum gauge is used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (for instance, −1 bar or −760 mmHg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as "gauge pressure".
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It is also given as inches of water gauge (iwg or in.w.g.), inches water column (inch wc, in. WC, " wc, etc. or just wc or WC), inAq, Aq, or inH 2 O. The units are conventionally used for measurement of certain pressure differentials such as small pressure differences across an orifice, or in a pipeline or shaft, [ 1 ] or before and after a ...
I think this page is misleading and inaccurate, but I am not enough of an expert to rewrite it. Firstly, Magnahelic appears to be a common misspelling of Magnehelic [1], which is a trademark owned by Dwyer instruments used to refer to their range of differential low pressure gauges. Secondly, they are used for many different applications, not ...
A third test method to determine if ductwork is leaking to the outside is to use a pressure pan, which is a register cover with a pressure tap for a hose connection. With the house pressurized (or depressurized) to 50 Pa (-50 Pa) using a blower door, a pressure gauge is attached to the pressure pan by means of a hose.
Further, the vacuum in the gauge eventually deteriorates due to slow diffusion of gases through the mercury, making the device inaccurate. [8] In 1938, Adolph Zimmerli (1886–1967) [9] invented a gauge that overcame the filling problems, at least for pressures below ambient pressure. [10] Zimmerli's gauge consists of three relatively wide columns.
The gauge may be used for pressures between 0.5 Torr to 1×10 −4 Torr. Below 5×10 −4 Torr, a Pirani gauge has only one significant digit of resolution. The thermal conductivity and heat capacity of the gas affects the readout from the meter, and therefore the apparatus may need calibrating before accurate readings are obtainable.
A dead weight tester apparatus uses weights to apply pressure to a fluid for checking the accuracy of readings from a pressure gauge. A dead weight tester (DWT) is a calibration standard method that uses a piston cylinder on which a load is placed to make an equilibrium with an applied pressure underneath the piston.