Furness controls FCO770, Руководство пользователя

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FCO770 Users Guide Issue 1 Page 13
METHODS OF LEAK DETECTION
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The test item (or the test item plus a reference volume if the test item has a large volume) is
filled to a set pressure/vacuum for sufficient time for the pressure/vacuum to become stable.
The pressure supply valve is then closed, and the test item and reference are connected to the
two sides of the differential pressure module.
Any leak will cause a pressure difference across the differential pressure module and the
resulting output is used to display the leak. A leak on the Test -ve port will show as a -ve
leak.
Leaks may be displayed as a flow reading rather than differential pressure. The FCO770
measures the leak as a pressure drop and then calculates the flow reading. The calculation
relies on the test volume being known as well as the pressure drop in a given time.
Alternatively a known leak can be connected to the test item and the volume automatically
calculated from this value. The advantage of using flow readings is that the test time is not so
important (a minimum of 0.3 seconds is recommended). As many leak specifications are
written in flow units it is easier to verify actual readings against the specification. Flow
conversions are carried out when the leak units are set to CC/S, CC/M, CC/H, CMMS,
mL/M, L/M, or mbLs.
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This is a variation of the differential pressure drop test that is used to test sealed items with a
test jig forming a chamber around the test piece. Additional valves are required for this test
Initially a charge (dump) volume is prefilled to a known pressure. When the test is started, the
charge volume is first isolated from the pressure source, and then connected to the test
chamber before performing a standard differential pressure drop test.
The actual test pressure depends upon the prefill pressure and the relative volumes of the
charge pressure and test chamber. If the test piece has a gross leak the test pressure will not
be as expected which is detected by the pressure tolerance check. Smaller leaks are detected
by the differential pressure drop test.
Variations in the prefill pressure may be compensated for to allow a more sensitive gross leak
check. Note that when compensation is enabled the displayed test pressure is the
compensated value, not the measured value.
The pneumatic configuration for a dump test is shown on page 83.