Analog versus Digital

(The Debate Continues)

There are two techniques used to handle vibration data. The selection of which is used should be based on the task to be performed with the data. The easiest way to explain the difference between these two signal processing techniques is to relate an analogy. If you wanted a precise control of lighting in a room you would install a dimmer switch, if you simply want the lights on or off you would install a standard light switch. The analog would be the "dimmer switch" and the digital would be the "standard switch", in this analogy. With an analog instrument the exact value of a signal is measured and often written down by the operator for future reference.

With a digital instrument, the signal is processed into a series of 1's and 0's and stored electronically for future reference. Most of these instruments do not have a high resolution display screen and are therefore similar to a camera, in that you must take them to a computer to "develop" the information. These instruments are often the choice of predictive maintenance technicians since the information can be gathered in a "hostile" environment and removed for analysis at a more convenient time.

Unfortunately, minor information is lost by digitally integrating the signal. The exact amount is primarily dependent upon resolution and sampling rates. In my opinion, the convenience of digital outweighs the difference in precision of the analog instruments for data collection in a predictive maintenance program.

Analog machines have their purpose in situations requiring on-site analysis and correction. Digital machine have significant shortcomings when low amplitude vibrations are present. A spindle running at 1800 RPM with a 0.02 in/sec vibration at rotational speed means the tooling or part is moving 0.0002 inches. This is not acceptable for many ISO / QS manufacturers, especially with parts having a +/- 0.0002 inch tolerance.

Since digital technology aspires to mimic analog instruments, I see the differences decreasing constantly. In some area it has exceeded analog, the best example is in Compact Disks (CD) versus the old vinyl phonographs.

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Last updated: November 24, 2002