When Digital Becomes Analog
Today’s digital displays look almost like real analog meters and can provide the same dynamic sensing.
Director of Precision Gages, Mahr Federal Inc.
Despite what some internet addicts might think, we humans are analog creatures. Think about trying to cross a busy intersection on foot, for example. If our senses were digital, we’d be limited to working with simple “on/off” information that would indicate that a car is present/not present. If we took several such “readings” over time, we would be able to extrapolate, but not directly detect, a car’s direction, speed and acceleration. By the time we had done all that, however, the car would be long gone and we’d have to start collecting data on the next one. We’d never get across the road. But because our senses are analog, a brief glance is all we need to detect the car’s presence, distance, direction, speed and acceleration. This enables us to react safely, either by staying put or crossing the road, or by varying our rate of acceleration somewhere along a continuous but finite scale of values.
Gaging devices that have an analog meter provide more intuitive information than digital ones. Just watching the needle sweep across the dial of an analog amplifier from “a little on the plus side” to “a little more on the plus side” may provide a machinist with all the information he needs to make the right decisions that enable him to maintain control over his process—even if he doesn’t actually read any numbers on the dial. So in spite of the benefits of digital instruments (more on this below), analog systems still have an important role to play in gaging.
Analog amplifiers also excel in “dynamic” applications where the gage head moves relative to the part (or vice versa). For example, when exploring parts for flatness using surface plate methods, the user slides the gage stand around on the plate and quickly observes the amount of variation in the part. If the user had a digital amplifier, he would have to position the stand, wait for a moment to read the value on the display, reposition the stand, read the display a second time and so on, until a sufficient number of data points had been collected.
Yet, while we like analog devices, manufacturing them is becoming more and more difficult and expensive. Volumes are low and the parts are many—a classic case for skyrocketing costs. The digital world may have to save the analog one.
One option has been simulating an analog meter through a digital display. A digitally created meter hand sweeps back and forth across a graduated meter background, giving the look of an analog display. The problem with this simulation had been that the analog hand on the digital meter did not have the smooth, eye-pleasing motion of a real analog display. This is fine for a meter on a car dashboard, on which the rate of change is relatively slow, but in a dynamic gaging operation, trying to find the high spot on a round part as it is being rotated is made more difficult by a jumping digital display.
The latest devices have evolved to the point that the digital displays almost look like real analog ones. The “needles” are clear and crisp, their movements fast and skip-free. And there is not the overshoot that is possible with needles on some analog meters. Today’s digital meters work just as well as, if not better than, true analog meters. When you combine the capability of an effective analog meter with that of digital display with high resolution, you make the human user happy and at the same time provide the digital information for precise data collection that makes your computer happy.
However, now that bench amplifiers combine the best of analog displays with digital precision, they have become rather like Range Rovers that never leave the pavement: Their full potential is rarely appreciated by their owners. Gaging amplifiers are often used simply as replacements for dial indicators where a higher degree of resolution is required. This is to ignore numerous opportunities to make gaging more efficient and productive.
Today’s bench amplifiers offer many more features at a much lower cost. Features like dynamics, tolerances, polarity, data output, preset values and auto-zero all are all pretty much standard now. If you’re using one of these amplifiers in place of an old indicator, take a look at the manual and see if there is an additional capability or two you can put to use. Or, if you need a new display for that classic gage, you should find that units available today do not require the large expenditure they did in the past.