Data Acquisition for Handheld Gaging
February 1, 2008
When looking for a system to handle data collected by handheld gages, there are two choices: wireless and wired. Both systems have their place in industry, and carefully considering the attributes of each will allow one to make the best decision.
Wireless System ComponentsA standard wireless data acquisition system for handheld gaging usually consists of three things: a transmitter interfaced to the gage, a receiver interfaced to the computer, and software that drives the receiver and collects data from the transmitter, allowing that data to be stored in the computer or transferred to a statistical process control (SPC) program. Both the transmitter and receiver of modern wireless data acquisition systems are often transceivers, meaning that they send and receive data. Because this functionality allows dialogue between the transmitter and receiver, it provides for the existence of system features that ensure data is received correctly by the computer. Virtually any gage, as long as it is capable of digital output, can be interfaced to a wireless system; the transmitter will connect directly into the gage’s digital output port.
Wireless SystemsToday’s wireless systems can accommodate as many as 120 gages and are capable of transmitting data hundreds of feet under ideal line-of-sight conditions. Furthermore, today’s systems incorporate a robustness and reliability not found in those of the past. This is in part enabled by the common use of transceivers, which helps combat data failure or corruption from electromagnetic interference (EMI) by enabling checks against transmission error. For example, a code can be assigned to a piece of data coming from the transmitter, and if the receiver finds that the code is corrupt, it will ask the transmitter to re-send that data until uncorrupted data is received. The use of transceivers also makes operator feedback possible; when, for example, the computer receives good data, the transmitter can alert the operator via audio and/or visual confirmation.
George Schuetz, director of precision gages at Mahr Federal (Providence, RI), explains how this concept relates to Mahr’s wireless system: “Besides the assignment of individual transmitter numbers to each transmitter, which provides a secure method of collecting data, each transmission supplements the measured value with an address number, a communication control word and a double check sum, thus providing absolute data security. A transmission error is recognized by the dialog between the PC and the transmitter. The transmission is repeated up to three times automatically within a few milliseconds.” After successful transmission of data, the transmitter alerts the operator with a beep and a flash of its green light in confirmation.
Another notable use of transceivers is found in The L.S. Starrett Co.’s (Athol, MA) mesh network concept. Not only does Starrett’s system provide checks against transmission error, its architecture is designed to give a higher level of robustness by taking a new approach to overcoming the common problem of EMI. A mesh wireless system interposes numerous routers between the gage’s transmitter and the receiver at the computer. So, for example, if a plume of interference keeps data from being sent to the receiver through the optimal router path, adjacent routers-which also have received the data though are not within the optimal path to the receiver-will relay that information to one another until the data is successfully received. At the same time, the transmitter continues to send additional data sets to the routers. After the receiver sees an exact copy of data it has already received, it stores the first data packet and discards additional readings.
A second feature of Starrett’s system is that the transmitters hold a queue of approximately 10 measurements, serving as a safety net in case a computer glitch occurs or an operator takes a gage outside of the network’s range. “Let’s say measurement four didn’t make it through, so it continues to try and try and try until the computer acknowledges a valid receipt of that measurement,” explains Jeff Wilkinson, general manager of advanced technology at Starrett. “And the computer doesn’t get rid of that queue of 10 measurements until they’ve all been serviced.”
While Sunriver, OR-based MicroRidge Systems Inc.’s GageWay wireless system is a true wireless system, it also can be configured to be what could be termed a hybrid system-combining both wireless and wired attributes. The system can be configured so that a receiver acts as a remote for wired RS-232 gages or other instruments for applications in which low mobility is appropriate. In this configuration two receivers are used, one at the PC and one near a workstation. The receiver near the workstation is connected to an interface from which cables run to RS-232 gages. This remote configuration using two receivers results in an increased transmission range compared to a configuration in which one receiver and battery-operated transceivers are used.
The GagesMost brands and virtually any type of handheld gage, such as a digital micrometer or digital caliper, can be interfaced to the wireless systems available today, provided that the gage has digital output capability. Gages will typically have BCD, RS232 (opto or direct) or a propriety type of digital output. Most wireless systems are available with transmitters for any of the above output types.
SPC SoftwareTypically, wireless systems will be compatible with virtually any SPC software, and propriety software is usually available from the manufacturer. Furthermore, manufacturers of wireless systems often offer basic and advanced SPC software. Mahr, for example, has an advanced software package that allows for the classification of good and bad parts via transmitter indication. “The software allows for tolerances to be assigned to the measurement, and when a good reading is measured a second green indication will be given of the value,” explains Schuetz. “If an out-of-tolerance part is measured, a second red signal will identify the bad part.”
Starrett bundles its wireless system with starter software, and also has three additional applications available for industrial-strength solutions. And customers also can use just about any third-party software; Starrett’s Wilkinson explains that, “SPC applications are many in the market. There’s a ton of them out there. With our system, customers can use applications such as InfinityQS or Prolink or even Mitutoyo’s MeasurLink, because all these applications are either supported by flat file or comport.”
Wired System ComponentsA standard wired data acquisition system for handheld gaging usually consists of three things: cables, a multiplexer and software that drives the multiplexer and collects data from the gage, allowing that data to be stored in the computer or transferred to an SPC program. Most manufacturers also offer a stripped-down system that supports a single gage; here the cable will connect directly into the computer, foregoing the multiplexer altogether. Virtually any gage, as long as it is capable of digital output, can be interfaced to a wired system; the cable will connect directly into the gage’s digital output port.
Wired SystemsWired systems can accommodate many gages and data transmission distance is relative to cable length. Wired systems possess an inherent robustness and reliability not found in wireless because cables preclude the possiblitly of data loss or data corruption that EMI-the scourge of the wireless system-can cause.
Traditionally, cable-to-computer and multiplexer systems use the RS232 input at the computer, but today more USB compatible systems are starting to become available. Of this development, Mahr’s Schuetz describes that multiplexer boxes typically handle four to eight gages and can be expensive; however, USB hubs, used in place of the traditional multiplexer, allow for multiple inputs and result in a less-expensive system. “Our USB system is unique in that it allows for the most cost-effective way to collect data from multiple gages,” states Schuetz. “The hardware, USB hubs and cables are very inexpensive and can be set up easily by the user. No special interfacing knowledge is required-USB is plug-and-play.”
Lancaster, PA-based Dyer Co. offers a custom multiplexer solution that accommodates various types and numbers of gages, as well as varying input and output formats. This is enabled through Dyer Measuring Buses (DMBs), modular components that connect with one another to create a train-like multiplexer that can be lengthened or shortened as needed. “It’s very adaptable, meaning you can wire other manufacturers’ indicators and micrometers-just about anything,” says Michael Scott, president of Dyer Co. “All the big names can link to it. It gives us a lot of flexibility, meaning that if you have a Mahr gage, we can do that. If you have a Mitutoyo digital indicator, we can do that.”
MicroRidge, too, offers a range of gage interface solutions. Its GageWay Series is highly configurable and can accommodate various numbers and brands of gages, as well as varying input and output formats. The multiplexers have chaining capability and can support conflicting port formats via adapter cables. An example of the series’ configurability is found in the GageWay SM, which connects a single Mitutoyo gage to a computer; this device comes in two varieties: one connects the gage to a USB port, the other to an RS232 port. The company’s Mx interfaces support multiple Mitutoyo gages and varying input and output formats. And for universal gage connectivity, the GageWay3 and GageWay5 interfaces can be configured to support an unlimited number of digital devices, while the GageWay4 and GageWay6 interfaces can be configured to support an unlimited number of serial devices.
The Gages and SPC softwareAs with wireless systems, most brands and virtually any type of handheld gage can be interfaced to the wired systems available today, provided that the gage has digital output capability. Gages typically have BCD, RS232 (opto or direct) or a propriety type of digital output. Like wireless systems, wired systems are typically compatible with virtually any SPC software, and propriety software often is available from the manufacturer. Furthermore, manufacturers typically offer basic and advanced SPC software. In terms of gage and software compatibility, there really is no difference between the two systems.
Weighing Pros and ConsParadoxically, one could make the case that a wireless system’s strength also is its weakness, and that at wired system’s strength, too, is its weakness. A wireless system has no wires-so it has the feature of increased mobility, with gages that are not tethered to a multiplexer or computer; but this also means that EMI can potentially creep up and ruin or impede an operator’s work. A wired system has wires-so it offers an inherent robustness, because EMI cannot compromise an operator’s work; but cabling also means reduced mobility and potential safety issues.
As Starrett’s Wilkinson explains, “Imagine having a tool with sharp jaws, like a slide caliper; now imagine having a tool like that with 20 feet of cabling running from it. You’re holding the tool delicately and someone walks by and trips on the cable, yanking it out of your hands with a lot of force. It could lacerate your hands very easily.”
Another problem with cabling is entanglement. “If you have five tools in a production area and they’re all wired to the same multiplexer, they will invariable get tangled,” explains Wilkinson. “At the end of the day, when they’re all tangled together, someone moves one and they all come down, which can ruin the tool or injure someone.”
There is the issue of cost. First, while the owner of a wired system has to pay for cabling, the owner of a wireless system has to replace transmitter batteries.
Secondly-and more importantly-are the disparities in initial system cost. A wireless system will typically be four to five times as expensive as its wired counterpart. Wireless systems, then, are only advantageous for specific applications. As Mahr’s Schuetz points out, “Wireless transmitters are relatively expensive and are often used in applications where cabling is difficult, usually where the gage has to be brought to the part-say in a machine-and the cables become a liability to the operator.” A scenario with few gages and easily handled parts, for example, would be better off with a wired system.
However, using a large number of gages in a wired system could offset its initial value. “Wireless systems are not inexpensive. But at a certain point, most of the multiplexers used in wired gaging become pretty expensive,” explains Wilkinson. “So once you get more than eight gages, it makes sense to go with wireless. In a large deployment, wireless is cheaper.”
While both wireless and wired data acquisition systems for handheld gaging are viable options in industry, the appropriateness of each is application specific. In terms of component versatility, both systems are equal, providing compatibility with virtually any third-party software and gage. Therefore, it is the environment in which the system is to be used as well as what it is to inspect that should guide one’s decision-making process. Q
For more information on the companies mentioned in this article, visit their Web sites:
- Dyer Co., www.dyergage.com
The L.S. Starrett Co., www.starrett.com
Mahr Federal Inc., www.mahr.com
MicroRidge Systems Inc., www.microridge.com
Mitutoyo America Corp., www.mitutoyo.com
Quality OnlineVisit www.qualitymag.com and type “Handheld Gaging” into the search engine to find related articles. Among the results you’ll find:
- “Quality 101: Practical Uses of Ring Gages”
- “Customizable Software Reduces Errors”
- “Keep Your Tools Working”
- “Data in the Palm of Your Hand”
- “Measurement Made Mobile”
Quality ApplicationsDealing with an Adverse Environment
Tuthill Pump (Burr Ridge, IL) decided to make the move to Starrett’s DataSure wireless system after an adverse shop environment ruined two multiplexers that supported a wired system. In the shop, parts are measured as they are machined, and because the multiplexers were located in the machining area, the debris from the machined parts ended up causing the failure of two units.
Today, the four gages used to measure the machined parts transmit data to a receiver located at Quality Manager Mike Wuethrich’s desk. “The only reason we went with the multiplexers to begin with was because the wireless system wasn’t available when we first started,” says Wuethrich. Wuethrich also enjoys the versatility and maneuverability that the wireless system affords.
Increased Accuracy and Reliability
Albany, OR-based Selmet Inc., manufacturer of small- to medium-sized titanium castings mainly for the aerospace industry, with a customer roster that includes Boeing, Rolls Royce and Pratt & Whitney, wanted to increase the accuracy of their handheld gaging data, while eliminating the man-hours spent manually entering that data in its computer system. Gage operators were taking measurements, recording those measurements on paper and then entering that data in a computer-an error-prone and laborious process.
There are several departments within Selmet that use handheld gages: dimensional, layout and wax. Selmet decided to start small and installed MicroRidge’s GageWay wireless system in the wax department, where it uses 6-inch, 12-inch and 24-inch handheld calipers as well as a 12-inch height gage.
“Testing the MircroRidge system out in our wax department has been a great success,” says Wade Conner, CAD engineer for Selmet Inc. “In the future we hope to roll this out to our much larger dimensional department. Not only is our data accurate, but we now have a growing database that can be accessed and analyzed as needed.”
Conner also notes that MicroRidge’s system was easy to set up. The system was up and running in a matter of minutes. Also, the system has worked flawlessly since installation.