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1．Introduction of ULVAC leak detector
ULVAC first launced the “DLMS” helium leak detector(HLD), on the market in 1967. Then in 1995, ULVAC started selling the “HELIOT 300 series”1) that made it possible to perform large leak and fine leak tests fully automatically for the first time in the world using our original“ select free” technology for the vacuum system.
Almost 20 years have passed since then. Ever since the launch of the “HELIOT 300 series”, we have developed several series of HLD for various applications, such as the “HELIOT 100 series”2) of compact and light-weight HLDs for customers who had not used HLDs before, the “HELIOT ZERO”3) HLDs exclusively used for automatic helium leak test systems and the “HELIOT 700 series”4) of general-purpose HLDs.
The HLD market is expanding from the vacuum, automobile, refrigeration, and nuclear power industries into the food and medical supply packing industry and other industries. Devices under test (DUT) and usage are also diversifying. Here we will introduce the “HELIOT 900 series” that was developed in such a market environment with the aim of improving the basic performance (measuring smaller leaks more quickly) and ease of use.
2．Lineup of leak detector
Figures 1 and 2 illustrate the appearance of the “HELIOT 900 series”. Table 1 lists the specifications. Two types of pumps are available just like the “HELIOT 700 series”: oil rotary pumps (W1 model: 30 L/min, W2: 135 L/min) and dry scroll pumps (D2 model: 90 L/min, D3: 250 L/min). A new D4 model dry scroll pump (pumping speed: 500 L/min) was just added for semiconductor and FPD manufacturing equipment. The W2, D3, and D4 models which have faster pumping speeds come with a mobile cart as standard equipment.
Connecting an optional sniffer unit allows the user to test DUTs by the snif fer method. This series was designed to make it possible to use different two methods －the vacuum method and the sniffer method－in a single unit.
3.1 Vacuum systems and analyzer tubes
The pumping speed of HLD test port needs to be increased in order to quickly start helium leak tests and to detect leaks in vacuum equipment and automatic leak testers with high sensitivity. However, when the pumping speed of turbo molecular pumps is increased, the amount of helium that reaches the analyzer tubes is reduced, which lowers the sensitivity. In the “HELIOT 900 series”, the pumping speed of the gas inlet ports of the turbo molecular pumps and the conductance of test valves were increased to achieve a pumping speed of 5 L/s (ultra flow). The improvement in the ability to detect micro currents (mentioned later) made it possible to detect leaks with high sensitivity. Figure 3 shows that the time to reach the pressure required to display a background level of 1×10－11 Pa・m3/sec for a DUT with a volume of 30 L was reduced by more than five minutes compared to the existing models. In addition, leaks were artificially developed in a chamber and an HLD was connected to test the DUT while discharging gas with a vacuum pump in the same way as when performing a leak test on vacuum equipment. The result was that leaks one-fifth (1/5) as large as those able to be detect by existing models were able to be detected.
Figure 4 illustrates the vacuum system of the“ HELIOT 900 series”. This model is equipped with the same“ selectfree” vacuum system as that used on the existing models, but the “HELIOT 900” has no function for switching between standard and high sensitive modes. Instead, the “HELIOT 900 series” has three flow modes: Gross flow (connecting pressure: 1,200 Pa), Fine flow (100 Pa), and Ultra flow (2 Pa) to measure fine leaks in addition to large leaks. The amount of flow during startup was modified and thus the startup time is no more than five minutes including calibration operations and no more than two minutes without calibration. The vent line has been changed to between the calibrated leak valve and calibrated leak, which prevents increase in the background during continuous operation. Moreover, the newly added D4 model is equipped with a roughing valve which can further reduce the time it takes to pump gas from a DUT.
The components used have also been changed. The Pirani vacuum gauge for monitoring pressure uses the newly developed “SPU”5), which sends the pressure signal to the main board by digital communication. The fore pump of the W1 model is a “GHD-031” made by ULVAC KIKO, Inc., and its magnetic coupling structure allows no oil to leak from the shaft seal, which extends the service life. In addition, an oil mist trap is provided as a standard accessory.
An electrode has been installed onto the analyzer tube to prevent secondary electrons that are produced when the inside of the analyzer tube is dirty or the pressure is high from hitting the ion collector, allowing for more reliable measurement.
Moreover, a hydrogen measurement mode, in which hydrogen can be used as the tracer gas like the existing models, is also provided.