Robotic leak testing is typically used in automated sniffer leak detection setups. A robotic arm moves the sniffer probe to the part to be tested to detect leaking test gas and its leakage rate. There are two types of robotic leak testing: stationary leak testing and dynamic leak testing. In stationary leak testing, the robotic arm moves to a defined location on the part and remains there for a defined time to determine any leaks and leak rates at that particular point. Dynamic leak testing is technically more challenging than stationary as the robot arm does not move to individual, previously defined locations. Instead, the probe tip moves on a continuous path along the surface of the test piece. The factors crucial to achieve reliable results in dynamic robotic sniffing: the speed with which the robot arm moves along the test part, the minimum distance from the part the sniffer tip can adhere to and how much air and test gas are sucked in by the leak detector.
Dynamic robotic sniffing should do two things. It should check a larger area of the test piece for any leaks and it should do so as quickly as possible for highest throughput, or to stay within the usually tight time constraint of the allowed cycle time. The problem is the smaller the leak rate, the slower a cloud of escaping test gas forms, which makes detecting the leak significantly more difficult.
For sniffer leak detection, whether by robot or manually, the air and the test gas are typically sucked in at the tip of the sniffer probe with a certain flow. The common unit for this gas flow is sccm (standard cubic centimeter per minute). Many conventional sniffer leak detectors draw in gas with a flow of only 60 sccm. With careful manual handling of the sniffer tip - at only a few test points, slow movement and keeping a short distance from the surface - this can sometimes be sufficient. But dynamic robotic sniffing is more challenging and demands higher flow to assure accurate detection.
If a component must be oil-tight, it is typically tested against leak rates in the range of 10-3 mbar∙l/s. In a laboratory setup, the effect of the scan speed of the sniffer tip on the detectability of leaks was recently tested. The tests took place with a test leak of 1 x 10-3 mbar∙l/s and the distance between the sniffer tip and the test piece was 6 mm. This distance was selected as a typical setup for robotic sniffing. (Getting closer to the test piece in a dynamic measurement could result in lack of accessibility or a collision with the product due to varying tolerances in the test piece.
The result of the extensive testing: conventional, commercially available sniffer leak detectors, which suck in gas with a flow of only 60 sccm, fail completely in this scenario. The probability of a leak of 1 x 10-3 mbar∙l/s being found by such devices is close to zero. Even devices that operate with a flow of 300 sccm are not suited for this application.
Only a device like the Protec P3000XL from INFICON, which is specifically designed with a flow of 3000 sccm, really meets the requirements of dynamic robotic sniffing. If the robot arm moves the Protec P3000XL probe tip over the surface of the test piece at a speed of less than approximately 14 cm/s (5.5 in/s), the leaks that are relevant to water-tightness are detected with 100% probability and localized. Only at a test speed of more than 14 cm/s did the detection probability decrease slowly.
If a component in the automotive industry must be tested for liquid fuel leaks, the leak rates are usually one order of magnitude smaller, i.e. in the 10-4 mbar∙l/s range. In the testing setup, with a distance of 6 mm from the surface of the test piece, but with a 10-4 mbar∙l/s test leak, neither the 60 nor the 300 sccm testers correctly detected a leak of this size, at any test speed. Also when using the Protec P3000XL, with its very high flow of 3000 sccm, the scanning speed should be slightly reduced. Dynamic sniffer leak detection with Protec P3000XL provides reliable results at speeds below approx. 8 cm/s (3 in/s) with leak detection rates of almost 100 percent.
Whether you intend to test for oil, fuel leaks or even smaller leak rates, it is important to note that for good robotic sniffer leak testing, it is mandatory to have the sniffing robot in a shielded area. For safety reasons, robotic stations are normally placed in some type of housing. To achieve highly reliable results make sure this booth also shields the robotic sniffer from any air movement in the production area.
Robotic sniffer leak testing eliminates the impact of a human operator, but it is essential to carefully select the leak detector based on the performance data required for the specific application. In many cases, this means that the robotic leak test can reliably detect and locate leaks only if the device takes in the test gas at a very high flow, for example 3000 sccm.
Our tip: Please talk to us if you are considering using robotic sniffer leak detection to ensure the quality of your products. We will work with you to determine which leak detector will help you achieve the optimum balance between reliability, speed and cost for your specific application.