Questions tagged [measurements]

Measurements, instrumentation, calibration and metrology.

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43
votes
9answers
8k views

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 ...
28
votes
10answers
6k views

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 ...
22
votes
3answers
1k views

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 ...
17
votes
7answers
4k views

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 ...
17
votes
3answers
4k views

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 ...
14
votes
3answers
5k views

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 ...
13
votes
3answers
4k views

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 ...
13
votes
2answers
7k views

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'...
11
votes
5answers
3k views

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 ...
10
votes
2answers
525 views

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 ...
10
votes
6answers
12k views

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 ...
10
votes
3answers
11k views

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 $x_0<x < x_1$. How do you ...
9
votes
3answers
8k views

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 ...
8
votes
4answers
4k views

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 ...
7
votes
5answers
1k views

What was that?! Quantifying the impact of a martial arts strike

Measuring things like a martial artist's strike can be challenging because it is a complex motion and common vernacular will use imprecise or incorrect terms. This question is an attempt to identify ...
6
votes
5answers
343 views

Can redundancy be used instead of periodic calibration?

A lot of production equipment requires periodic calibration as part the documentation that the equipment is under control. The companies selling the equipment knows this and sometimes lowers the price ...
5
votes
2answers
501 views

Seeing through walls and noninvasive structural integrity metrics

Walking into a building, how does one find out where the pipes are, how strong the walls are (currently) and other key structural integrity measures? without breaking walls or utilising harmful-to-...
5
votes
3answers
162 views

Measuring the road surface quality

First of all, excuse my little knowledge, I'm a computer programmer by trade and unfortunately have very little knowledge of physics, engineering, DSP but I'm willing to learn. I would like to ...
5
votes
1answer
127 views

How does an ultrasound device determine where the reflection is coming from?

When the ultrasound transducer emits a signal and the signal comes back to the receiver how does the software or hardware determine where it came from? I understand it finds distance or depth by delay....
5
votes
1answer
326 views

How can I detect black spots?

I am researching about ways to continuously determine black spots (size 50+ micron) in our product stream. This stream consists of imperfect spherical polymer beads (size 3 mm) of different materials (...
5
votes
2answers
216 views

Anomalous oxygen in aluminium sample SEM EDS

I have a sample of aluminium which I'm interested in finding the rough composition of. The sample is a part of a large number of samples which I sanded down and polished with a polishing table. I ...
5
votes
1answer
7k views

How can I calculate the evaporation rate for a hazmat spill?

I was given formulas for general evaporation, for a spill calculator I am building. These are formulas, that are supposed to approximate evaporation, are for a number of different chemicals. ...
5
votes
2answers
805 views

How to evaluate new Vernier calipers?

I am looking to purchase some new Vernier calipers, but I am overwhelmed by the amount of specs which are being offered. I need help in understanding how to evaluate them. I do not want a dial or ...
5
votes
1answer
825 views

How do I calculate rolling resistance for tire on pavement?

First condition assuming perfect rolling, no slip, from what I understand is that the rolling resistance coefficient can be calculated as the displacement arm of the normal force the tire "feels", in ...
5
votes
1answer
461 views

LabView or another software for experiments [closed]

I used LabView for a lot of my BME undergrad, but the labs focused mainly on things dealing electrical signals. In the real world I'm working mostly on ME projects, but we lack a good deal of ...
5
votes
1answer
423 views

How to measure turbulence parameters experimentally?

When running CFD simulations with turbulence on, I often need to specify inlet parameters such as the turbulent intensity, turbulent viscosity ratio and/or the turbulent length scale. If these ...
5
votes
1answer
92 views

High-resolution Z stage distance measurement

I am designing a 3-stage platform like that of a 3D printer. Three stages correspond to X, Y, and Z axis. There is a nozzle with fixed height about the z-stage platform. The stages are pretty ...
5
votes
1answer
137 views

Question about “uncertainty”

I'm a bit confused about all the different "definitions" of uncertainty? One can calculate "uncertainty" of a single measurement by simply checking how accurate the tool that is being used to do the ...
4
votes
2answers
2k views

Can we build a tool that measure curvature on an arc?

I know some biologist that are taking curvature measurements on photos with softwares to understand the variation on beak morphology. I'm wondering if there is a way to build a mechanical tool (or ...
4
votes
3answers
2k views

How does a frequency to voltage converter work?

I am measuring the rotational speed of a shaft using a disk with 60 cuts and an optical fork. The signal from the optical fork is sent to a frequency to voltage converter and after that to a data ...
4
votes
3answers
669 views

Is it Possible to Automatically Transform an Image of an Object into a Line Drawing in AutoCAD?

I have many photos of devices which must be traced into AutoCAD. Is there any software for tracing object edges/outlines automatically so that a Primary Plan of the object can be made in AutoCAD? For ...
4
votes
3answers
329 views

What organization specifies unit of measure conversions?

A recent work project involved a number of unit conversions between various systems of measurements. Due to the scale and critical nature of the project, we wanted to ascertain that our conversion ...
4
votes
1answer
569 views

How can I accurately measure the actuation force of small buttons (<1cm diameter) using home equipment?

I'm trying to measure the actuation force of buttons on the Playstation Vita, in preparation of building an external device that presses these buttons automatically. Specifically, I'm trying to ...
4
votes
2answers
566 views

Determine volume of liquid in a fluid bladder

I am trying to determine if it is possible to "physically" determine the volume of liquid (such as water) in a non-solid container like a fluid bladder like this or this? Assume that it is not ...
4
votes
1answer
948 views

Uncertainty Calculation of LVDT displacement transducers for length measurement

I have to calculate the uncertainty of measurement for an LVDT Linear displacement transducer used for measuring length. Uncertainty calculations are ruled by ISO 17025 but there are no (at least ...
4
votes
1answer
696 views

How do you convert “kps” to Pounds per Square Foot (psf)? [closed]

I'm looking at a soil bearing capacity report, which has a column labeled "kips" and the values are followed by "kps". A "kip" is 1000 pounds, but I'm not sure how to convert from "kps" to psf. The ...
4
votes
2answers
69 views

Is there a way to distinguish between U.S. Customary and British Imperial volumetric units?

I am used to the metric system where everything is simple and consistent. I can do quick conversions between metric and imperial in my head, but especially when it comes to volumetric measures, I ...
4
votes
1answer
488 views

Tracking location and direction without GPS?

How can I track a device's location (x,y,z coordinates) as well as the direction the device is facing (north, south, up, down, etc.)? Standard accelerometers are not precise enough for very small ...
4
votes
2answers
319 views

Weight Sensing Problem: Need to detect 10kg load down to milligram accuracy

So I need to build some type of scale where one can place four 600mL beakers on it and measure out its weight down to a milligram level of accuracy. I'm doing this so I can dose a very small amount of ...
4
votes
2answers
256 views

How can I determine how many cycles to average for when taking a measurement using Lock-in Amp if I know sensor spectral noise density?

I am taking a phase sensitive measurement of an AC magnetic field using an SR830 Lock-In Amplifier and a magnetic sensor. I know I have to average over a number of measurement cycles to get an ...
3
votes
3answers
237 views

Mechanism for controlling the clamping force

I am working on upgrading a research project on wind energy. They are trying to measure the performance of wind blade designs in a small wind tunnel (i.e. their models are relatively small). What they ...
3
votes
1answer
11k views

What is the “tl” unit of weight measurement?

I recently purchased a digital scale from eBay. According to the listing it can weigh in the following units: Multiple Weighting Units: g, oz, tl, ct. Screenshot of that page: Now I know that "g"...
3
votes
2answers
772 views

Are there different Gauge standards out there?

It is my understanding that a mil is a one thousandth of an inch (1mil = 0.001”). Also, a mil is 25.4 microns, aka micrometers. Then, it is my understanding that Gauge is 100x mil (1mil-100Ga). I am ...
3
votes
3answers
15k views

How much current is this phone drawing?

I know the current should be higher than 0.67 mA, because I know phones use current in the order of 1A. Also the charger is able to support up to 1A, it doesn't make sense that the charger would have ...
3
votes
2answers
5k views

What does 12 bit resolution mean?

I'm looking at this inclinometer and in the features it says "12 bit resolution." I'm looking for a resolution of up to a 1/10th of a degree but don't understand what the 12 bit resolution means.
3
votes
3answers
109 views

Making precise, intricate measurements

What's the best way to precisely measure intricate mechanical parts? For example, notice the tiny differences between the pitch in these two threads, and the tiny variations in external width of the ...
3
votes
1answer
5k views

What is the difference between tolerance and uncertainty in measurement?

Please explain with theoretical concepts and a brief example.
3
votes
2answers
243 views

Measure the distance to a balsa wood strip with 1 mm accuracy

I am working on a project where I need to determine the density of a balsa wood strip. I know the length and height of the strip. The two measures left to take are the weight and the thickness of ...
3
votes
3answers
3k views

Rule of Tens/Ten to 1 Rule in Measurement and Inspection

I'm trying to clarify my understanding about the requirements [read: best practices] for measurement resolution and measurement confidence. The "Rule of 10s" is a commonly tossed around guideline ...
3
votes
1answer
193 views

What does L mean in Uncertainty Measurement Result U(E)=0.08+1.2L ;k=2? [closed]

I'm calculating the combined measurement uncertainty u(c) of a measurement for a length displacement sensor. Amongst other factors, one individual uncertainty affecting the error of measurement is the ...

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