Apparatus and method for automatic leak detection
An apparatus for automatic leak detection, including a chamber to enclose a test specimen. A vacuum pump is in selectable fluid communication via an adiabatic noise cancellation valve with the chamber. A pressure transducer determines a pressure in the test specimen and transmits a pressure signal to a controller. The controller is to control the adiabatic noise cancellation valve to cause the vacuum pump to draw a vacuum from a space between the test specimen and the chamber thereby creating an adiabatic noise cancelling condition in which a temperature of the test specimen is stabilized. The controller is to control a flow of a test gas into the test specimen, and to determine a pressure decay rate from the pressure signal. The controller is to determine if the test specimen meets a leak test specification based on the pressure decay rate under the adiabatic noise cancelling condition.
1 . An apparatus for automatic leak detection, comprising:
a chamber to enclose a test specimen, the test specimen having a pressurizable volume that is pressurizable when leaks are smaller than a predetermined threshold;
a vacuum pump in selectable fluid communication with the chamber;
an adiabatic noise cancellation valve to selectably open and close the selectable fluid communication between the vacuum pump and the chamber;
a differential pressure transducer connected to the test specimen and a reference volume for directly determining a pressure difference between a pressure in the test specimen and an other pressure in the reference volume, and for transmitting a signal indicative of the pressure difference to a controller, wherein:
the apparatus is configured to operate when the test specimen is at least 5 degrees Fahrenheit warmer than the reference volume; and
the reference volume is located:
outside of the chamber and the reference volume is at ambient temperature, or
within the chamber and the reference volume is at a chamber temperature; and
the controller to control the adiabatic noise cancellation valve to cause the vacuum pump to draw a vacuum from a space between the test specimen and the chamber thereby creating an adiabatic noise cancelling condition in which a temperature of the test specimen is stabilized, an electronic pressure switch and electronically controlled valve to control a flow of a test gas through parallel ports of the electronically controlled valve into the test specimen and into the reference volume to reach a predetermined test pressure; the controller to determine a pressure decay rate from the signal indicative of the pressure difference; the controller to determine if the test specimen meets a leak test specification based on the pressure decay rate under the adiabatic noise cancelling condition.
2 . The apparatus of claim 1 wherein the test gas is air.
3 . The apparatus of claim 1 , further comprising an infrared reflective barrier disposed between the test specimen and at least a portion of the chamber to reduce infrared radiation heat transfer between the test specimen and the chamber.
4 . The apparatus of claim 3 wherein the infrared reflective barrier includes a polyamide layer having a natural polyamide color.
5 . The apparatus of claim 3 wherein the infrared reflective barrier is to enclose at least a portion of the test specimen and blocks at least 90 percent of infrared energy exchanged between the test specimen and the chamber in an absence of the infrared reflective barrier.
6 . The apparatus of claim 3 wherein the infrared reflective barrier is non-outgassing to an extent that outgassing from the infrared reflective barrier does not induce or enhance a transfer of heat energy to or from the test specimen during a test cycle.
7 . The apparatus of claim 3 wherein the infrared reflective barrier includes a reflective surface disposed on a plastic substrate to reflect infrared radiation, wherein the reflective surface includes a layer of aluminum foil, wherein the layer of aluminum foil is at least one of: attached to the plastic substrate by an adhesive, or deposited on the plastic substrate by vapor deposition.
8 . The apparatus of claim 1 , further comprising a thermal insulating pad to support the test specimen in a test position and to reduce conduction heat transfer between the test specimen and the chamber.
9 . A method of automatic leak detection, comprising:
cycling an adiabatic noise cancellation valve to activate adiabatic noise cancelling conditions;
checking for a stable temperature in a test specimen by using a differential pressure sensor connected to an internal volume of the test specimen and a reference volume, wherein:
the test specimen is at least 5 degrees Fahrenheit warmer than the reference volume;
the reference volume is located:
outside of a vacuum chamber surrounding the test specimen and the reference volume is at ambient temperature, or
within the vacuum chamber and the reference volume is at a chamber temperature;
the differential pressure sensor is to determine a pressure difference between a pressure in the test specimen and an other pressure in the reference volume; and
wherein the differential pressure sensor is to transmit a signal indicative of the pressure difference;
monitoring of a vacuum level in the vacuum chamber to determine if the adiabatic noise cancelling conditions are achieved;
starting a differential pressure decay instrument to monitor the signal indicative of the pressure difference over time to determine a pressure decay rate in the test specimen;
determining a leak test result based on the pressure decay rate under the adiabatic noise cancelling conditions;
dumping pressure from the test specimen; and
dumping vacuum from the vacuum chamber.
10 . The method of automatic leak detection of claim 9 , further comprising blocking an infrared heat exchange path between the test specimen and a surface of the vacuum chamber via an infrared reflective barrier disposed between the test specimen and at least a portion of the vacuum chamber.
11 . The method of automatic leak detection of claim 10 wherein the infrared reflective barrier includes a polyamide layer having a natural polyamide color.
12 . The method of automatic leak detection of claim 9 , further comprising supporting the test specimen in a test position with a test fixture that includes a thermal insulating pad that provides thermal insulation to an extent that conduction heat transfer through the thermal insulating pad is to induce less than 1 percent error into the leak test result.
13 . The method of automatic leak detection of claim 9 , further comprising reducing infrared radiation heat transfer between the test specimen and the vacuum chamber by disposing an infrared reflective barrier between the test specimen and at least a portion of the vacuum chamber, wherein infrared radiation heat transfer between the test specimen and the vacuum chamber is to induce less than 1 percent error into the leak test result.