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Is Your Spidey Sense Tingling?

The July 2011 issue of Hydraulics and Pneumatics magazine featured an interesting application story about how hydraulics systems were designed and used in the “Spiderman: Turn off the Dark” Broadway musical.  The article describes some of the challenges faced by motion systems designers, and how those challenges were solved.

One particularly challenging aspect of the hydraulic motion systems was the requirement that multiple hydraulically driven platforms had to be raised and lowered simultaneously.  The motion of the platforms had to be very precisely controlled, making hydraulic component selection critical.

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Linear Sensor Basics: Absolute vs. Incremental

When it comes time to choose a linear position sensor, there’s a dizzying array of options and terminology to wade through.  In this series of articles, we’re going “back to basics” to try to shed some light on the sometimes confusing world of linear sensing options, technologies, and terminology.

First up, we’re going to take a look the two basic linear sensor measurement types: absolute measurement and incremental measurement.

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The Power of 2

In numerous types of analog position sensors, resolution is expressed in terms of bits, e.g, 8-bit, 12-bit, 16-bit, etc.  But what does that really mean?  In a previous entry, I discussed what I called Digitally Derived Analog Signals, which provides a basic overview of how Digital-to-Analog Converters (DAC’s) are used to generate analog sensor signals.  You may recall from that entry that when someone says a sensor has “16-bit resolution”, what they really mean is that the sensor employs a 16-bit DAC, which is capable of processing 216 discrete values, and representing any one of those values as a corresponding analog signal.

To help better understand what these binary numbers actually mean, I thought it might be helpful to provide a quick-reference chart showing the equivalent decimal values of numbers from 20 to 232.

(click to enlarge)The values in bold represent some of the more commonly used DAC’s for industrial sensors.