Control Engineering

Well, not really. Again, we have that slippery word accuracy. (see Ask Charlie for Sept. 29, 2008) Everyone uses it; everyone assumes they know what it means; and everyone assumes that everyone else knows what they mean when they say it. The truth is that accuracy is poorly defined, nobody really has a handle on what it’s supposed to mean, and so nobody really knows what somebody means when they say it.

Then we have the phrase “running controls,” which is in a lot better shape. I’ll try to make quick work of the “running” part. In this context, it means something like “putting into operation,” or “incorporating into the system.”

Remember the old saying: “Making n...Read More

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This question came in as a comment to my June 16, 2008 posting: How old is the RCA connector standard?

The author claims to have noticed a size difference between RCA connectors from different manufacturers. This should not be. While RCA connectors are manufactured by a large number of manufacturers, all are intended to fit together, so they all have compatible connections defined by the international standard IEC 6095...Read More

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I can’t be too specific about a recommendation for reasons that will become clear later. There are is a wide selection of cameras, each adapted to a fairly narrow range of applications. It all depends on what you want to do with it.

There is no “general purpose industrial camera” that is appropriate for all industrial applications. Off hand, I can think of about five classes of digital cameras of interest in industrial applications. I’ll give you a rundown on all of them, so you can choose what most closely matches what you want to do:

Industrial photography — Handheld or tripod mounted cameras equivalent to the 35-mm SLR cameras so loved by professional photographers everywhere are still around. They just capture images on CCD or CMOS based image sensors instead of photographic film. Yes, there are still film cameras...Read More

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No, practical nuclear reactors vary from microscopic to pretty darn big. That said, the practicality and efficiency of a given plant depends on its purpose and type. Commercial nuclear reactors intended to provide electricity for the national power grid, for example, should be as big as possible given the available technology. The cost of building and operating a plant with twice the power output is not twice as great.

At the highest level, there are three types of nuclear reactors:
Radioisotope thermoelectric generators obtain power from spontaneous radioactive decay;
Controlled fission reactors obtain power from a nuclear fission chain reaction;
Fusion reactors obtain power from a controlled thermonuclear fusion reaction.

Fusion reactors
I’ll start at the top level by disc...Read More

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This question came as a response to the "Accuracy vs. Precision" posting of Sept. 29, 2008. The full text of the question is:
"How do I accurately request a free pocket protector as a gift for my husband when I cannot even understand what he does for a living with any precision, much less understand your articles?
To be precise, I am a classical musician who loves my engineer husband dearly and think he would get a kick out of having one of your pocket protectors. ;-)"

Obviously, you already have asked. Requesting is easy, getting is another matter. As my wife has been known to say: "It"s good to want things. It builds character!"

The pocket protectors aren’t free. A longtime friend of mine, pundit, cookbook publisher, sausage maker, and writer of articles about high technology, ...Read More

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This question relates to an episode of Mythbusters intended to air in January 2009. Control Engineering got advance notice of the event from Grant Smith President of data-acquisition specialist Dewetron USA, which helped in making the episode: 

“We have helped the Mythbusters on three different occasions so far. The most well-known one so far was the Birds on a Truck episode, from 2007. But on September 19, 2008, we were asked to come to San Francisco again and help the team with another myth from an upcoming show. Perhaps you remember the car commercial from a few years back, which sh...Read More

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The short answer is that everything needs calibration!

The full text of this question is: “In the aerospace company I work in, all CNC systems are calibrated regularly, and adjusted as required. These have incremental encoders. We have robots in some of our thermal spraying cells where motion repeatability is not as critical. We are planning a new robot-based processing system where ensuring repeatability and accuracy remain the same. Time is important. The robot uses absolute encoders (and goes through self-checks on each start-up), therefore, the manufacturer states that no calibration is necessary. Is this your view? How then do we ensure that the robot is within specifications and retains that?”

What tests are needed?
Just this morning I was talking about high accuracy motion control with Kevin Kauf...Read More

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Accuracy and precision are used to describe properties of a measurement. The science of making measurements is called metrology. At first, it might seem that there isn’t much to it: you just take an instrument, and make a measurement, and you’re done, right? Wrong!

As soon as you look below the surface, metrology rapidly becomes arcane. In the mid-1990s, I started a magazine called Cal Lab, the audience of which was qualified metrologists. We did a study of how many such metrologists existed. It came out to about 5,000. That’s not just “English-speaking metrologists,” or “metrologists living in North America.&rdquo...Read More

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Mean time between failures (MTBF) is a simple way of quantifying a repairable system, subsystem, or component’s reliability. While not specifically a control-oriented parameter, understanding it can help control engineers compare components during system design, recommend system maintenance procedures, and is especially important for designing high-reliability control systems. Ostensibly, MTBF indicates how often the unit being specified will have to be repaired when kept indefinitely in service.

MTBF is often confused with a related specification — mean time to failure (MTTF) — which applies to replaceable, rather than repairable units. Most assemblies manufactured today are non-repairable units. They are made to be discar...Read More

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Or, "What beautifully complex machine was turned on recently and didn’t consume the earth in a black hole as some uninformed detractors tried to say it would?"

This question refers to startup of the Large Hadron Collider (LHC), which saw its first beam last Wednesday (Sept. 10, 2008). LHC is located at the European high-energy physics facility CERN on the Franco/Swiss border. Don’t ask for a decoding of the acronym. You wouldn’t like it even if it were possible!

In the Standard Model of particle physics, hadrons are a class of sub-atomic particles that have relatively large masses. &ld...Read More

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A resistance temperature detector (RTD) exploits the fact that the resistance of most metals increases with increasing temperature. To first order, the resistance of an RTD is given by 

R = α(T-T0) + R0,

where T₀ is a baseline temperature, R₀ is the RTD’s resistance at that temperature, and α is the resistance temperature coefficient for the RTD metal. The most common type RTD is made from platin...Read More

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The best way to sense electric current depends on the size of the current and the impedance of the circuit it’s passing through. My three favorite methods are shunt resistors, op-amp current-to-voltage convertors (CVCs), and Hall effect current sensors. All are ideal in their application “sweet spots” and can be problematical otherwise.

A shunt resistor is the simplest method for measuring current. It is simply a small-value resistor connected in series with the load. Typically, they are installed in the low-voltage side of the load where it connects to ground or neutral so that measuring equipment and personnel are not exposed to high voltage. In most applications, the resistor value is well under an Ohm. 

...Read More

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