Calibration steps for vacuum leaks-comparison method
The analog method of calibrating a vacuum leak compares the effect of the gas flowing out of the vacuum leak with the reference specification. To prevent errors caused by non-linearity and drift of the measuring instrument, the reference specification should be as close to the value of the vacuum leak as possible.
Gas microflow meter static analog method
As shown in Fig. 6, the gas QL flowing out of the vacuum leak hole and the gas Q flowing out of the gas micro-flow meter are separated and introduced into a vacuum chamber, and then sucked away by the vacuum pump through the restriction hole, as if they were in a vacuum chamber. The static offset pressure input signal (separated as HL and Hs) generated in the, and then the leak rate of the vacuum leak hole is calculated by using formula (9).
QL = (HL / Hs) Qs (9)
One of the key skills in this step is the gas microflow meter. Table 1 shows the technical indicators of vacuum leak hole installation calibration by the American Standards Skills Research Institute (NIST), the German Physical Skills Research Institute (PTB), and the Chinese LIP.
Reference leak static analogy
Comparing the input signal HL and Hs of the reference leak in the leak detector with the calibrated vacuum leak and the known leak rate, use formula (10) to calculate the leak rate of the calibrated vacuum leak.
Where H0 is the background signal of the leak detector; as and aL are the thermal coefficients of the reference leak and the calibrated leak; △ Ts, and △ TL are the calibration reference leak and the calibrated leak and the reference heat The deviation. Then Qs and QL are on the verge of being close to each other. The biggest source of error in this step comes from the value of Qs. Therefore, the reference leak used as a reference specification must be regularly calibrated with the gas micro flow specification or the remaining high-precision relative leak rate specifications. . This step is easy and practical, and many leak calibration laboratories use it to continue to calibrate practical reference leaks (as reference leaks for non-transmission and delivery specifications).
Quantitative gas dynamic analogy
After accumulating gas in the volume V for a period of time from the calibrated vacuum leak, a partial pressure will be formed. This partial pressure will continue to be compared with the standard partial pressure with a mass spectrometer, and then the leak rate of the vacuum leak can be lost. The standard partial pressure can be lost by dynamic shrinkage or accumulation of effluent gas from leaks with known leak rates.
American SNL loses the normative partial pressure by the dynamic contraction method, as shown in Figure 7. A small container V. is filled with a calibration gas having a pressure of Pt (the depth is C) and is contracted into the large container V as a standard pressure. For previous calibration points, a small container V. was used to sample from the large container V, and then dynamically contracted into Vm, and the partial pressure signal Hs was measured by a mass spectrometer; then the calibrated reference leak was passed through the time Δt in the volume Vx. The gas accumulated in No. 2 contracted dynamically into Vm, and its partial pressure signal Hx was measured by a mass spectrometer. The leak rate QL of the calibrated reference leak was initially calculated using the following formula
Relevant chapters browse:
Summary of vacuum leak calibration steps
Calibration steps for vacuum leaks & mdash; & mdash; constant pressure varactor method
Calibration steps for vacuum leaks & mdash; & mdash; constant volume variable pressure method
Calibration steps for vacuum leaks & mdash; & mdash;
Calibration steps for vacuum leaks & mdash; & mdash; analogy