Leak test method and apparatus

A differential pressure type leak test apparatus for testing a work for leaks based on variations in the pressure difference between said work and a master, said apparatus comprising:

• a high-pressure gas source;
• first and second conduits for interconnecting said high-pressure gas source and said work and said master through first and second valves, respectively;
• a third valve connected between said first and second conduits, for permitting and inhibiting the passage therethrough of gas between said master and said work;
• a differential pressure sensor connected between said first and second conduits, for detecting the pressure difference between said master and said work;
• a sequence control part which generates a time sequence for opening, and closing of said first, second and third valves and a time sequence for detecting said pressure difference by said differential pressure sensor in a drift calculating mode and in a leak test mode;
• a valve control part placed under the control of said time sequence by said sequence control part, which, in said drift calculating mode, opens said first and second valves to introduce therethrough high-pressure gas into said work and said master from said high-pressure gas source and, prior to measuring first and second pressure difference variations, opens said third valve to establish a pressure equilibrium between said work and said master, and thereafter closes said third valve and which, in said leak test mode, opens said first and second valves to introduce therethrough high-pressure gas into said work and said master from said high-pressure gas source and, prior to measuring a third pressure difference variation, opens said third valve to establish a pressure equilibrium between said work and said master and thereafter closes said third valve;
• a drift calculating part placed under sequence control by said sequence control part, which, in said drift calculating mode, executes in said first and second pressure difference variation measurements a process of obtaining first and second pressure difference variations by detecting pressure differences at a first time after the closing of said third valve and at a second time a predetermined time after said first time and calculates a drift from said first and second pressure difference variations;
• a leakage calculating part placed under sequence control by said sequence control part, which, in said leak test mode, obtains a third pressure difference variation by detecting pressure differences at the first time after the closing of said third valve and at the second time a predetermined time after said first time and subtracts said drift from said third pressure difference variation to obtain the leakage from said work;
• and
• a pass/fail decision part which compares said leakage with a leakage reference value and decides that said work is leak-free or leaky, depending on whether said leakage is smaller or larger than said leakage reference value.

A leak test method in which:

• pressurized gas is introduced into a master and a work connected to a high-pressure gas source via first and second valves, respectively;
• the pressure difference between said master and said work is measured by a differential pressure sensor;
• a pressure difference variation per unit time is calculated from a measured value of said pressure difference;
• a drift is subtracted from said pressure difference variation to obtain a leakage;
• and said leakage is compared with a leakage reference value to determine if said pressurized gas leaks out from said work;
• said method comprising the steps of:
• (a) opening a third valve connected between said work and said master to establish a pressure equilibrium therebetween, and then closing said third valve;
• (b) measuring a first pressure difference variation per unit time;
• (c) opening said third valve, after said step (b), to establish a pressure equilibrium between said master and said work, and then closing said third valve;
• (d) measuring a second pressure difference variation per unit time after said step (c);
• (e) calculating said drift from said first and second pressure difference variations checking to see if the type of said work currently under test is different from the type of the previously tested work;
• and
• (f) checking to see if a change in the temperature of said current work is larger than a reference value;
• wherein if the result of at least one of said checks is affirmative, a drift calculating process by said steps (a) to (e) is executed;
• and if the results of both of said checks are not affirmative, measuring a pressure difference variation of said work under test as a third pressure difference variation in said measurement period, and subtracting said drift from said third pressure difference variation, comparing the absolute value of the result of said subtraction with a leakage reference value, and deciding if the work under test is leaky or leak-free depending upon whether said absolute value is larger or smaller than said leakage reference value.

A leak test method in which:

• pressurized gas is introduced into a master and a work connected to a high-pressure gas source via first and second valves, respectively;
• the pressure difference between said master and said work is measured by a differential pressure sensor;
• a pressure difference variation per unit time is calculated from a measured value of said pressure difference;
• a drift is subtracted from said pressure difference variation to obtain a leakage;
• and said leakage is compared with a leakage reference value to determine if said pressurized gas leaks out from said work;
• said method comprising the steps of:
• (a) opening a third valve connected between said work and said master to establish a pressure equilibrium therebetween, and then closing said third valve;
• (b) measuring a first pressure difference variation per unit time;
• (c) opening said third valve, after said step (b), to establish a pressure equilibrium between said master and said work, and then closing said third valve;
• (d) measuring a second pressure difference variation per unit time after said step (c);
• and
• (e) calculating said drift from said first and second pressure difference variations wherein said measurements of said first and second pressure difference variations in said steps (b) and (d) are performed, in said steps (a) and (c), by closing said third valve, then resetting the reading of said first detected pressure difference value at said first time, and obtaining, as said pressure difference variations, said second detected pressure difference value at second time a predetermined time Δt after said first time.