Pressure Decay Leak Testing in Automation
In automated manufacturing many assembled products require leak testing to validate product viability and quality. A leak test is used to determine if an assembled object, product, or system functions within a specified leak limit. Leaks occur when gas or liquid flow through an object via an imperfection or manufacturing defect such as holes, cracks, weak seals, etc.
The automation of leak testing generates several key challenges, such as real estate on a production line, strict quality standards, efficient productivity, as well as communication and data sharing with the rest of the automation equipment.
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Proximity is Key
Square footage on a production line is valuable and costly. Leak testers are often integrated into assembly lines however they best fit. Many standard pressure decay leak testers measure over 12” wide. A common solution for integration is to extend the connection hoses between the part under test and the leak tester which can be several feet away. The longer the connection tubing, the more volume is used in a leak test, which can have a devastating effect on productivity as well as the accuracy of leak tests.
The volume of air used in a leak test includes the internal volume of the tester, the volume contained in all of the connection tubing, as well as the volume of the product under test. The farther a leak tester is from the part under test the larger the test volume. The larger the volume the longer the volume takes to pressurize which negatively effects productivity and throughput.
A higher test volume can also impede the leak testers ability to detect a leak. Think of this in terms of tires. You have a car tire which holds a large volume and a bike tire which holds a small volume. If both tires run over the same nail, what happens? The bike tire flattens almost immediately while the car tire slowly loses air over time. The smaller the test volume the faster and easier it is to detect a leak. The larger the test volume the longer it takes to identify if there is a leak, meaning extended test times with a lower accuracy of detection.
In terms of instrumentation, when running a pressure decay test, the value attributed to the pressure decay is the digital signal from the pressure sensor. When testing objects with the same size hole, such as a bike and car tire, the object with the larger test volume (car tire) will translate into a smaller signal than an object with a smaller test volume (bike tire). The pressure decay value is directly proportional to volume. Smaller signals require more time to detect a leak. Electrical, pneumatic, thermal or atmospheric effects, or noise, can mask small signals as well as influence the pressure decay value which has a negative impact on repeatability. A smaller total test volume yields a larger relative pressure decay value/signal and requires less test time. The greater the magnitude of the signal above zero, the better signal to noise ratio, which directly results in higher test accuracy and repeatability.
Moving the leak tester closer to the part under test will decrease test time and increase accuracy which raises both quality and throughput. The challenge is how to narrow that proximity when space is so limited? The answer is the iKit by Zaxis. At 1/4th the size of most pressure decay leak testers the iKit was designed specifically to fit within close proximity to the product under test on an assembly line. At only 3” wide the iKit can be mounted right on tooling saving valuable space and reducing excess test volume that is created by the use of extended hoses.
Effective automation relies on effective communication. There are many components that go into an automated production line, all of which need to be able to talk to each other. Once a leak tester runs its test it needs the ability to communicate results or trigger events such as Pass=Next, Fail=Eject or Fail=Halt Production.
There are many forms of communication commonly used in factory automation including Modbus, Ethernet TCP/IP, and EtherNet/IPTM. The most dynamic of these communication systems is EtherNet/IPTM as it combines traditional Ethernet infrastructure and hardware with both of the most commonly used collections of Ethernet standards, the Internet Protocol suite and IEEE 802.3, and integrating the Common Industrial Protocol. EtherNet/IPTM is the preferred communication system for Allen-Bradley automation equipment.
With factory automation in mind, the purpose-built design of the iKit has the option to include EtherNet/IPTM. Other communication systems such as discrete I/O, RS232 and Ethernet TCP/IP are also available.
iKit Automation Solution
Zaxis has designed the iKit to be the ideal leak tester for factory automation settings. With the smallest footprint of any pressure decay leak tester on the market combined with integrated Allen-Bradley connectivity, the iKit by Zaxis is an excellent leak test solution for factory automation.