Air tightness testers need to display the leak rate (sccm or cc/min). For air tightness testers using the direct pressure method and the differential pressure method, the instrument must be compensated and calibrated before displaying the leak rate. That is, connect a leak-free standard workpiece to find the system zero point, and then connect a leak orifice with a fixed leak rate to this leak-free workpiece system; the test result and the fixed leak rate value of the leak orifice need to correspond to the parameter values.
Ambient temperature refers to: changes in the temperature surrounding the air tightness tester. Or changes in the temperature of the test workpiece itself. Or changes in the temperature of the piping from the air tightness tester to the workpiece under test.
Temperature changes affect the measured leak rate. If conditions such as the test workpiece and fixture remain unchanged, a temperature increase causes the gas to expand, and the expanded gas reduces the pressure change, so the measured value becomes smaller than the original value. If the workpiece under test has good sealing performance,
In this case, a negative value may occur.
The volume of the product under test may change. In actual testing, we have encountered this: when testing an engine oil gallery, the customer mistakenly injected oil into the gallery, reducing the volume. At that time, the test value showed a large negative value. A sudden change in volume may cause the test result to decrease and produce a negative value. A change in volume will cause the test result to show a negative value.
If the fixture and piping deform, the total test volume may change. This can also cause negative test results. For example, during testing, neither the workpiece nor the piping itself leaks, but the sealing rubber on the fixture undergoes creep, which causes the pressure inside the piping connected to the workpiece to rise, potentially producing a negative value.
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