Engineering Tolerance And Surface Finish Symbols

Cassini Captures Ice Queen Helene

NASA's Cassini spacecraft has successfully completed its second-closest encounter with Saturn's icy moon Helene, beaming down raw images of the small moon. At closest approach, on June 18, Cassini flew within 4,330 miles (6,968 kilometers) of Helene's surface. It was the second closest approach to Helene of the entire mission.

Cassini passed from Helene's night side to the moon's sunlit side. It also captured images of the Saturn-facing side of the moon in sunlight, a region that was only illuminated by sunlight reflected off Saturn the last time Cassini was close, in March 2010.

This flyby will enable scientists to finish creating a global map of Helene, so they can better understand the history of impacts to the moon and gully-like features seen on previous flybys.

The closest Helene encounter of the mission took place on March 10, 2010, when Cassini flew within 1,131 miles (1,820 kilometers) of the moon.

Plasma Spectrometer Operations on Hold
Pasadena CA (JPL) Jun 16 - Mission managers for NASA's Cassini spacecraft suspended operation of the Cassini plasma spectrometer instrument on Tuesday, June 14, 2011, after a series of voltage shifts on the spacecraft. They will determine when the instrument can resume collecting data.

The Cassini spacecraft is designed to operate with a "balanced" voltage source to create a tolerance to short circuits. On May 1, a voltage shift occurred, most likely explained by a short circuit happening somewhere in the system.

On June 11, a voltage shift in the opposite direction occurred, indicating an additional short circuit. In both cases, all instruments and engineering subsystems continued to operate properly.

Analysis of telemetry data from the spacecraft by the engineering team pointed to the Cassini plasma spectrometer instrument as the cause of the voltage shifts. The instrument has additional capacitors in the power lines for noise reduction.

The concern was that one or more of these capacitors may have short-circuited, which would cause the voltage to shift and explain the observed changes. Although the instrument was operating properly, engineers decided to turn it off as a precaution until the events could be better understood.

The suspension of the plasma spectrometer operations is not expected to affect other science data gathering or navigation.

Healthy & Nutrition » Blog Archive » Overview of Push in fitting ...

The concept of push in fitting has been around for decades, yet it has only seen significant growth in the U.S. water market since the early 1990s. Since then, push in fitting have been—by many accounts—the fastest-growing technology change in the water industry.

With their initial entrance into the U.S. water markets in the mid-1980s, push in fitting had to overcome many obstacles of misperception. Dealers and installers couldn’t believe something so simple could work reliably. Old methods of connecting tubing (compression and barbed fittings) were difficult to let go for fear of trying something new and innovative. However, as leading edge technologies were changing the water market, more and more installers and OEMs started enjoying the labor-saving and reliability benefits of push in fitting. The rapid acceptance of push in fitting during the 1990s has established them as the connection technology standard for today’s water industry.

Applications push in fitting have found their place in the water industry. Their most common use is for general tubing connections in RO and water filtration systems. However, push in fitting are also used on water valves, tanks, pumps and faucets to ease installation and increase system reliability.

Push in fitting can also be found in installations of water fountains, water coolers, ice machines, juice and beverage dispensers and coffee brewers.

Fitting Construction While push in fitting require complex engineering design and precise, high-quality manufacturing to produce, they are quite simple to understand and utilize.

Push in fitting are made up of three basic components—the fitting body, a flexible “collet” and an O-ring.

The fitting body can be made from metal (brass, stainless steel) or plastic (acetal, polypropylene). The body has an internal geometry to precisely house the collet, O-ring and tubing when assembled. Fitting bodies come in many configurations such as tees, elbows, unions and threaded connectors.

The collet is typically made from plastic with stainless steel gripping teeth molded into its flexible legs. The collet teeth provide a firm grip on plastic or copper tube. The flexibility of the collet legs allows for easy insertion and release of the tubing.

The O-ring is usually made of a food-grade rubber compound (nitrile, EPDM). It is seated inside the fitting body and forms a seal on the outside diameter (O.D.) of the tube.

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