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step-1:remove the pressure gauge from the equipment when machine is in off condition.
step-2:remove the cap and glass of the gauge.
step-3: remove the needle of the gauge with a needle puller( a special tool )
step-4: place the same needle indicating zero.
step-5: fix the glass and cap as usual.
step-5: check(calibrate) the gauge on a dead weight tester with a master degital pressure gauge.
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How do you find zero error of screw gauge?
Take a measurement with nothing in the gauge. That reading is the zero-error.
What is Zeroing Error?
Suppose say you have plastic rule new one. There you will be having zero marking. When you have to measure the length of a rod then you would keep zero marking at one end of the rod and the marking where the other extreme of the rod is taken to be length of the rod. say it is at 4 cm. So 4cm is the length. And suppose the ruler is an old one whose edge got damaged. Now you don't have zero marking so visible there. So you have keep the end of the rod at say 1 cm marking. Now the error that we commit is known as zero error. Here the error is positive. ie +1 cm. So as the other end of the rod is at 5cm marking then the correct length is got by applying zero correction. As zero error is +1 cm, then zero correction would be -1 cm So the correct length 5-1 ie 4 cm. Same way in case of vernier, if zero of vernier is at left side of zero of main scale, then the zero error is negative. If zero of vernier is right side of zero of main scale then error is +ve as we have seen in the earlier old ruler case. Same way in case of screw gauge as the head scale zero is above pitch line then error is negative and as head scale zero is below pitch line then zero error is positive.
What is a pressure gauge?
A pressure gauge is an instrument that measures the pressure in a vessel, a line, or whatever the pressure gauge is connected to. Pressure gauges come in at least two different types: differential pressure gauges, and absolute pressure gauges. Differential pressure gauges measure - surprise - DIFFERENCES in pressure. Pressure gauges that read "zero" when not attached to anything would actually be differential gauges that measure the difference between atmospheric pressure and the pressure of whatever they are attached to. Vacuum gauges are differential gauges that measure how far BELOW atmospheric pressure the pressure is in a vessel or pipe. Gauges that measure "gauge pressure" are just differential gauges that are calibrated to measure zero at atmospheric pressure. Absolute pressure gauges would only read "zero" if they were attached to an absolute vacuum. A common type of absolute pressure gauge is a barometer. Strictly speaking, a mercury barometer is really a differential gauge that measures the difference between the vapor pressure of the mercury and the surrounding atmosphere, but the vapor pressure of the mercury is so low that the error in treating it as an absolute pressure gauge is generally negligible. There are many different kinds of gauges used to measure pressure including: Instruments hydrostatic - These measure pressure according the height of a liquid in a column. The height of the liquid is proportional to the pressure. Common types of hydrostatic gauges include: manometers, McLeod gauges, and piston gauges. aneroid - The pressure sensing element may be a Bourdon, a diaphragm, a capsule, or a set of bellows, which will change shape with changes in the pressure of whatever the gauge is attached to. The deflection of the pressure sensing element is read by a linkage connected to a needle or by a secondary transducer. The most common secondary transducers in modern vacuum gauges measure a change in capacitance due to the mechanical deflection. Gauges that rely on a change in capacitance are often referred to as Baratron gauges. Electronic sensors thermal conductivity - including two wire and one wire gauges that measure pressure via changes in the thermal conductivity of the wires as they are placed under strain. Something like this is used in a lot of electronic bathroom scales. ionization gauges - These are primarily used for measurements of low-pressure gasses. They sense pressure indirectly by measuring the electrical ions produced when the gas is bombarded with electrons. Fewer ions will be produced by lower density gases. they have to be calibrated against another type of pressure gauge and depend on the gas being measured.
What is zero correction?
the correction which is made to get correct measurement after zero error
Why negative symbol is used to show vacuum?
No common vacuum units that I know of use negative values for a vacuum. Although pressure is an absolute quantity, everyday pressure measurements, such as for tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other ad hoc reference. When distinguishing between these zero references, the following terms are used: Absolute pressure is zero referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure. Gauge pressure is zero referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted. Differential pressure is the difference in pressure between two points. The zero reference in use is usually implied by context, and these words are only added when clarification is needed. Tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, and altimeter pressures must be absolute. Differential pressures are commonly used in industrial process systems. Differential pressure gauges have two inlet ports, each connected to one of the volumes whose pressure is to be monitored. In effect, such a gauge performs the mathematical operation of subtraction through mechanical means, obviating the need for an operator or control system to watch two separate gauges and determine the difference in readings. Moderate vacuum pressures are often ambiguous, as they may represent absolute pressure or gauge pressure without a negative sign. Thus a vacuum of 26 inHg gauge is equivalent to an absolute pressure of 30 inHg (typical atmospheric pressure) − 26 inHg = 4 inHg.
