Capacitance film vacuum gauge is an absolute pressure, total pressure measuring vacuum gauge, the principle is to add on the capacitance of membrane stress change of the change of the distance between the diaphragm, which produced the change of capacitance, again through the discriminator capacitance change into the change of the current or voltage, composition for the output signal, so, it is measured directly reflects the change of the vacuum pressure value, and only related to pressure, has nothing to do with gas components, namely: the film vacuum gauge is a direct measurement, the total pressure type vacuum gauge.
Capacitive membrane vacuum gauge principle according to the elastic thin film under the effect of differential pressure producing strain caused by the capacitance changes made of the principle of vacuum gauge is called capacitance film vacuum gauge, it is composed of capacitor
film regulation (
Also known as the capacitive pressure sensor)
And the measuring instrument of two parts.
According to the different methods of measurement of capacitance, instrument structure have offset method and the zero method two kinds.
It is composed of capacitor film gauge, measuring bridge circuit, dc offset, low frequency of power supply, low frequency oscillator, phase sensitive detector and indicator, etc.
Capacitive membrane tube in the middle of the pack is now a metal elastic diaphragm, on the side of the diaphragm is equipped with a fixed panels, when the pressure difference on both sides of the diaphragm is zero, the fixed electrode and diaphragm form 'static capacitance Co, after it with series capacitor C1 as measuring bridge bridge arm, capacitance C2 and C3 and C4 with other three Cs series capacity of bridge arm.
Metal elastic diaphragm isolates film vacuum gauge tube into two rooms, respectively by vacuum measurement and control system in the wave of the room and high vacuum measurement and control system (
The reference pressure chamber.
In the two room of connecting pipe.
Set a high vacuum valve 7.
When measuring, open the valve 7, first with high vacuum extraction system space on either side of the diaphragm pump all reference pressure gauge tube pbe and adjust the measuring bridge circuit, balance, namely the indicator refers to zero.
Then, close the valve 7, measuring chamber through the vacuum system being measured.
Unilateral double capacitance film vacuum gauge has a high sensitivity, the dielectric constant of the gas is constant, the pressure reading completely unaffected by gas composition, reaction speed, etc.
Such as the regulation reference indoor add buy getter device and smoke to l0 or less ° 5 pa, can measure absolute pressure zlO 'pa.
Thin-film vacuum gauge disadvantages of vacuum gauge was not without his faults, first is the price is high, the domestic is commonly 4 -
The amount of 6000 yuan, low expensive limits;
Imports are 1.
About 50000 yuan/only;
Second, domestic old-fashioned film gauge to zero drift, requires constant correction, often requiring correction.
Mainly is the old technology, domestic materials science is relatively backward, temperature stability is bad;
There is also a little span range, the domestic no more than 3 orders of magnitude.
The third is the old-fashioned rules rules capacitance temperamental, easy to bad, know the used degree, oil pollution in are difficult to clean, with acetone, save 13 tend to scrap cleaning, small range of 2/3 would be a bad film capacitor parameters related to the electric capacity of capacitor is the characterization of the parameters of the capacitor to store charge ability, it is equal to the stored charge on the plate in the numerical quantity Q and the plate on the ratio of the voltage U.
Capacitance in 684 using digital counting method, the counting method is commonly 3 digits, one of the most on the left side of the first and middle number is a valid number, most the right side of a number is said multiples, also is how much power of 10, if there is no marked unit, the general default is pF.
If it is with the number of decimal point, and at the same time shows no unit, the unit is uF.
Thin film capacitor similar pronunciation and pronunciation of the new color ring resistance, coefficient of three digits of the top two are, the last one is the index of 10.
104 is 10 times 10 to the power of 4, equal to 100000 pf, namely 100 nf.
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