Engineering Stack Exchange
Engineering Stack Exchange

Questions tagged [measurements]

Measurements, instrumentation, calibration and metrology.

Questions about measurement, instrumentation, calibration and metrology. Covers both automatic and manual measurement.

Also questions about conversions between measurement units, and official standards for engineering and scientific measurement.

See also the tag of metrology.

281 questions
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Is it possible for a bicycle chainwheel to have a fractional number of teeth?

Background In the world of bicycle motocross, also known as BMX racing, gearing is a hotly-debated topic. Since the bikes are all single-speed, gear ratio is a fixed number defined as chainwheel / cog (front gear divided by rear gear). Altering your…
eckza
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How to quantify martial arts strikes?

Subtitled: Ah, strong am I with the Force, but how do I measure it? With all due apologies for paraphrasing Yoda, I am trying to measure a force. Fortunately, it's an easier force to measure than midi-chlorians. When I tutor others in karate, one…
user16
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3 answers

How to know whether the flow is supersonic in a nozzle?

For a project I had built a convergent divergent nozzle designed for Mach number = 3. In that project, I could know the flow has gone supersonic by seeing the manometer fixed between the throat and the divergent section (drop in pressure, as the…
Subodh
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How can I measure correctly with a ruler?

When measuring with a ruler divided into mm lines, should I include the lines by themselves or only in between them? I illustrated the problem. (I took an example of measuring of 10 mm with two long lines just to make my point, but my question is…
Ubiquitous Student
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3 answers

How does measurement uncertainty combine with tolerances?

Given a tolerance within which your workpiece should be manufactured, say some length should be $10\pm1$mm. If you determine that your uncertainty in measuring this length is $0.2$mm (at 95%). How should a measurement of $9.1$mm be treated? Clearly…
nivag
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15
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1 answer

What unit of weight is that?

Recently I was weighting stuff with my dad and as I was playing with one of the old 2 kg weights I felt with my fingers number "5". After cleaning and upon further inspection it turned out the writing on the weight says "5Φ". We checked and it…
elementiro
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3 answers

Can I use a ultrasound sensor to measure water level?

If I use an ultrasonic sensor will it detect the water level? I was thinking about a product to read water level on water boxes (common in Brazil). I researched about instrumentation for this measure, and I think that an ultrasonic sensor is the…
Henrique Oliveira
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How does a multimeter protect itself from high voltages?

I have used a cheap multimeter to measure voltages in simple DC circuits, but I have seen pictures of them plugged straight into the mains and used to measure various home-built generators. Why doesn't the higher voltage fry the multimeter, and also…
jhabbott
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Measuring longer distances with high accuracy

I am involved right now in the fabrication of steel structures on the order of 5-50 feet long. Presently, we measure these structures with garden variety commercial tape measures. Most of the time, we work to a tolerance of about +/-1/16" and don't…
Ethan48
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6 answers

Distance sensors with accuracy of 1 mm?

I am making a device for measurements. I would like to measure the distance within accuracy of 1 mm. Range could be 2 cm to 15 cm . I looked at Proximity Sensors but the readings displayed by these sensors are not steady. I wish to measure the…
JustCurious
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11
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Practical setup to measure angular velocity

I have got a spinning top from a Canadian manufacturer, and I am deeply amazed by how neatly it spins. My interest in physics has led me to try to find out at what top speed I can spin the top and how that compares to other tops made from other…
DK2AX
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10
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3 answers

How do you determine the accuracy of a measurement device?

Lets say you have a measurement device of which you do not know the accuracy, and a reference measurement device. Both measure a variable $x$. The range of interest is $x_0
JHK
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10
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6 answers

What instrument does a surveyor use to accurately find North?

The obvious answer is a compass. I have an old (1952) transit that has a compass which seems to be accurate to 15'. However, that doesn't seem too incredibly accurate at all. Furthermore, most modern digital theodolites I see don't appear to have a…
canadianer
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How is gas flow through (extremely long) pipelines monitored and controlled?

(This is closely linked with measuring the Mach number inside a nozzle but it is not regarding the supersonic flow) Friction and heat transfer have effects on the Mach number of the compressible flow (Fanno and Rayleigh flow). As it is extremely…
Subodh
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9
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3 answers

What are grads used for on a scientific calculator?

Every scientific calculator I've come across has a DRG button that controls whether trigonometric functions use units of degrees, radians or grads yet I've never seen or heard of any system that actually uses grads. When is the grads setting useful?
cup
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