Smith designed what is believed to be the world's first "digital" micrometer, and received a patent sometime between 1890 and 1893, according Dr. Victoria Beauchamp, a Mitutoyo-funded researcher for The Hawley Collection, University of Sheffield (Sheffield, England). The device, which was not electric as today's digital tools are, used a mechanical display that showed inch measurements three ways: 10ths, 100ths and 1,000ths. It allowed his workers to quickly and accurately take measurements.
Ciceri Smith's desire to make a micrometer easier for his workers to use may be more than a century old, but today's quality experts also have that desire. Experts such as Wilson Silva, quality engineer at the automotive component manufacturer Dana Corp. (Toledo, OH), for instance. Silva says that he uses digital tools because he found that the measurements that are taken are more accurate and that training new employees is quicker.
The same can be said of Chris Blanton, quality manager for Accurate Bushing Co. (Garwood, NJ), who uses handheld digital tools. "These tools are used to take dimensional measurements of high tolerance aerospace parts, which we fabricate," he says. "Our dimensions call for very tight tolerances, ranging up to 0.0001 inch in requirements, so digital is the only way to go. Digital tools, while certainly more expensive, tend to function better, give more accurate readings and require somewhat less training than do their analog counterparts. The old analog style does not give us as precise a reading."
A slow start
Electronic, digital handheld tools have been around for more than three decades, but they were somewhat slow in their acceptance. Today, many suppliers say that digital tool sales are equal to or greater than nondigital tool sales.
"Early on, they were still somewhat mistrusted by the measuring and manufacturing world," says Steve Pike, group manager, precision measuring tools, Mitutoyo America Corp. (Aurora, IL). "The first ones were just okay. Not just Mitutoyo's, but all manufacturers' early versions. We struggled with trying to make a tough, reliable and dependable digital tool with a battery life that was pretty good and a display that was readable in low-light conditions," he says. "Now, we have built six or seven generations of digital calipers and it is our most popular tool."
The digital micrometer took a little longer to catch on, probably because of the tool's extreme tolerances. Dave DiBiasio, national sales manager for Brown & Sharpe (North Kingstown, RI), says the jump from the analog micrometer to the digital micrometer was a profound advancement because of the extremely small measurements that the digital version can take. "With a standard micrometer, there is a main barrel scale that breaks the inch down to a 1/10 inch, another scale on the barrel that breaks it down to thousandths, and a vernier scale on the barrel that breaks it down to 10,000ths of an inch," he says. "Picture trying to use this in a standard shop environment, which may not be well lit, and trying to look at one scale, then turn the micrometer over and look at another one and go to a third to see which lines are lining up. All to try and determine that reading. Without skill, there is a huge potential for error."
The electronic nature of new micrometers has allowed manufacturers to go beyond even these miniscule measurements. Today's digital micrometers can read down to 50 millionths of an inch, DiBiasio says.
Digital is not just confined to calipers and micrometers. A slew of handheld measuring tools such as ultrasonic thickness gages, hardness testers, surface analysis tools, height gages, torque wrenches, gap and flush transducers and others have all added electronic capabilities.
Ease of use is a big reason; it is much easier to read a number than to count numbers on a vernier scale or lines on the barrel of a micrometer. The growing use of statistical process control (SPC) is another reason. In the past, results would be noted with paper and pencil, a time-consuming process that can lead to transposition errors, papers getting smudged by contaminants and, most importantly, out-of-tolerance conditions that are allowed to continue because some data analysis is not immediately accessible. Digital tools of all stripes usually are available with RS232 serial ports to connect via cable to a personal data assistant, portable data collector, or laptop or PC computer. This eliminates errors by cutting out the paper step, and also makes SPC analysis of measurement data available more quickly, sometimes in real time. In at least one case--Fowler's new wireless caliper that uses fiber optics--the cable isn't even needed.
"Training is a big issue for companies," says Fred V. Fowler III, president of Fred V. Fowler Co. Inc. (Newton, MA) "The caliper is a basic instrument and can be used right out of the box. Even digital calipers are simple enough that they usually have one or two buttons on them--inch or metric, on or off. They can be hooked up to SPC, although that isn't as big a part of the business."
Another improvement to digital tools is the improvement in battery life. Compared to earlier generations of digital tool batteries, which didn't last as long and may have required more than one battery to operate, most batteries today will enable a tool to operate for a year or more in normal day-to-day use. The long life of the battery helps users not worry about it giving out at just the wrong moment, when trying to take a difficult measurement or when measuring in an inhospitable place.
Another recent innovation in calipers is that tool manufacturers are providing more protection against the environments in which the tools will be used. Today's digital slide calipers with LCD screens and data ports are vulnerable to moisture, dust and grime.
"The reading scale of the caliper must be kept clean and dry," says Mitutoyo's Pike. "If operators are using it close to a machine that is flooded with coolant, at the very least, their hands are going to be wet and they will most likely hold the tool on the area that the caliper has to slide over to read. And this could generate errors."
To minimize these risks, toolmakers recently have begun to more securely seal the electronics and to include moisture resistant coatings on the display.
In recent years, many caliper suppliers have begun to rate their tools based on an International Protection Rating (IP). Many tools have carried an IP-54 rating, but in a little more than a year, three companies have introduced calipers with an IP-65 rating. The IP rating system was developed by the International Electrotechnical Commission to rate tool products. Under the IP classification, a tool has a Class 6 rating for foreign matter, which indicates that the tool is protected against the entry of any dust or larger particulates. The Class 5 water protection rating means that the slide caliper is not subject to adverse affects from direct jets of water dousing it from any direction. This represents a more protected tool than an IP-54 rated tools that carries a Class 5 rating, which states that it will prevent most dust, and a Class 4 rating, which means that it can be used around splashing water. Currently, there are three calipers offered with an IP-65 rating: Mitutoyo's Absolute Coolant Proof Calipers, Brown & Sharpe's Dura-Cal IP65 and Fred V. Fowler's Sylvac Ultra-Cal Mark IV.
These manufacturers have succeeded in making the caliper fairly impervious to the shop-floor environment. Many manufacturers add that the same technology can be used across the board in other handheld devices. And so, it appears that handheld tools of the future will continue to have more capabilities, be tougher and more reliable, and be easier for the workers to use. It sounds as if these tools would have been a welcome addition in Ciceri Smith's wire mesh shop.
- Early manufacturers recognized the need to make it easier for workers to read measuring tools.
- Today's electronic handheld measuring tools, such as digital calipers and micrometers, offer ease of use, increased accuracy and long life.
- Digital calipers are now appearing on the market that have been rated to protect the tool from an ingress of dust or water jets hitting the tool from any direction.