Quality measurement: Dirt Does Hurt
January 16, 2007
IP rating is used to specify the environmental protection of electrical equipment. The first number describes protection against solid objects. The second number describes the protection against liquids. The commonly omitted third number describes the protection against mechanical impacts. For example, a gage with an IP65 rating is totally protected against dust and is protected against low-pressure jets of water from all directions with limited ingress permitted.
Even with the added protection, Schuetz says that is it important to remember that a caliper is still a caliper and are sensitive to operator use. “Calipers have to be used properly to get good measurements. Calipers, no matter how rugged, are only good to a certain degree of performance-usually only to 0.0005 inch or 0.0001 inch, but nothing better-because of their inherent design.”
While electronic calipers continue to evolve, Chris Penna, design engineering manager at SPS Industries (Farmington, CT), expects further developments. “In the future, we expect that digital calipers will reach IP68, which is the highest IP rating obtainable,” Penna says. “These calipers would be totally protected from solid particles of any size, and would be able to sustain long periods of immersion in water, under pressure.”
Such advancement would mean manufacturers would no longer need super powers to eliminate the enemy.
The Tesa-Cal IP67 Digital Electronic Caliper, with IP67 compliance, gives this precision measuring instrument protection against contamination from water and coolant mist, dust and metal particles, and other airborne contaminants typically found in production environments. Main components are encapsulated for protection against liquid and particulate penetration. This caliper is liquid proof to 10 feet, making it durable enough to be cleaned with a high-pressure air hose. The caliper is designed to measure outside and inside diameters, depth and steps. The unit includes instant inch/metric conversion and a 1/4-inch LCD with automatic shutoff after two hours. It has a resolution of 0.0005 inch (0.01 millimeter) and a measuring range of 0-6 inches (0-150 millimeters), and is available with or without a thumbwheel.
Brown & Sharpe Tesa, A Division of Hexagon Metrology
The new IP67-rated coolant proof SuperSolar digital caliper, powered by a solar battery charging a super capacitor, is capable of operation under low-light conditions and has the ability to run on capacitor power when experiencing even lower light conditions. The unit’s housing is sealed dust-tight and has passed a temporary water immersion test proving harmful effects are not possible when the enclosure is temporarily immersed in water under standardized conditions of pressure and time. IP67 certification means the new digital caliper is dust-proof, chip-proof, coolant-proof and immune to the tough conditions found on the production floor. The caliper can be submersed in coolant and provide 0.01 millimeter resolution with ±0.02 millimeter accuracy.
Mitutoyo America Corp.
CornerCalipers are capable of accurately measuring distances to theoretical sharp corners, apexes, mold lines or points of intersection. Sheet metal parts, plastics, castings, extrusions, or any part with slanted, drafted or rounded walls can be measured without complex measuring systems.
With IP65 protection, the 797 electronic caliper series is resistant to coolant, water, dust, dirt and metal chips. The calipers have an LCD with 0.310-inch characters, zero at any position, instant inch/millimeter conversion, manual on and off with auto-off after 4 hours of non-use, and a CR2032 battery with more than a 3,500-hour life. All 797 Calipers include an RS232 output port for collecting and outputting data. The units meet DIN862 linear accuracy and have a 0.0005-inch resolution. A fine adjustment and slide lock further ensure precision measurements. The calipers are available in a variety of sizes and measuring ranges: 0-6 inch (150 millimeters), 0-8 inches (200 millimeters) and 0-12 inches (300 millimeters).
Starrett Co., The L.S.
The water-resistant MarCal EW series digital calipers line, with an IP67 rating, is available in ranges from 6 inches (150 millimeters), 8 inches (200 millimeters) and 12 inches (300 millimeters). All models are available with or without a thumbwheel. Technicians can select from either a round-rod style or a flat-rod style. All calipers have dirt wipers integrated into the slide, lapped guide ways and hardened stainless steel slide, beam, and inside and outside measuring blades. A reference lock function provides zero setting capability. The MarCal 30 EW digital depth gage has the features found in the caliper line. The 16 EW and 40 EW digital micrometers, rated IP65 for dust and water resistance, have satin chromed steel frames with heat insulated holders, lapped carbide tipped anvils, hardened throughout spindles, rapid drives and integrated ratchets for repeatable measuring force. The 16 EW is available with a measuring range of 0-1 inch (0-25 millimeters).
Mahr Federal Inc.
Dirt is the enemy. Still, no matter how dirty the manufacturing environment, measurements need to be taken and have to be accurate. To address these concerns, calipers have evolved over the years.
Conventional calipers offer only limited protection against the liquids and dirt in a shop environment. “When liquids and dirt penetrate the inner workings of the caliper they cause problems with the gears and rack that control the caliper’s movement,” says Lee Kirtlink, marketing manager at Brown & Sharpe Tesa, A Division of Hexagon Metrology (North Kingston, RI). “Machinists have traditionally taken great care to protect their calipers from this environment by taking their parts away from the process to collect their measurements and carefully cleaning and returning their caliper to their toolbox after each use.”
But sometimes the harsh environments cannot be avoided and a more robust solution is needed. “When we talk about ruggedized calipers or micrometers, we are talking about making a caliper work in a harsh environment. Now you can get your caliper dirty or wet and it will still work,” says George Schuetz, director of precision gages at Mahr Federal Inc. (Providence, RI). “That does not mean that you will make a good measurement. The part and the jaws on the caliper are still going to have to be clean. Dirt on the jaw will cause errors in measurement, so having the most rugged caliper will not improve the measurement.”
Schuetz says that the idea behind the rugged caliper is to make the caliper survive if it is dropped into the coolant tank or splashed with oil, making the tool last longer out on the shop floor.
Electronic calipers have become more popular on the shop floor since the 1980s but have not been an option for use in environments where liquids are used. Within the last four to five years companies are now addressing Ingress Protection (IP), says Scott Robinson of the Technical Support Department, L.S. Starrett Co. (Athol, MA), thereby increasing use of electronic calipers on the shop floor.