distance measurement - micrometer

[fazhols]

Hi All. My first post here so please go easy!

I need to design a cheap simple device to measure distance variations. The key being the word variation.... which will be from 0 to 5mm with accuracy/rsolution to a micron (10^-6m)

Having looked at some historic posts using IR, UV led with sensor is a good option. my proposed design will be telescopic with the sensor facing the led so no concerns about reflection properties. Also, the sensor and the led can be up to 150mm apart (or a bit more if it helps). Unit can be closed so no external light interference.

Measurement can be of light intensity or more involved circuitry to measure timing differences of signal.

I would prefer not to use an interferometer which will be too sensitive, pricey and too fiddly to set up.

What I havent found on other posts is the resolution and accuracy that can be expected from the LED route.

Any information and/or ideas that you have will be greatly appreciated.

[edit] I have considered hamamatsu PSD's but have no infor on cost]
Thanks

 

[ZekeR]

Don't know too much about this topic, but here's my 2¢...

Determining distance with timing differences from light will be very tricky for such small variations. Consider that light travels at 300Mm/s; traveling 1µm will take 3fs (3 femtoseconds); consider that a 1GHz processor's clock runs at 1ns between clock pulses, which is 300,000 times longer than the period you'd like to measure. Measuring a 3fs difference would take some serious work. Modern TOF cameras resolve ~1mm, which translates to about 3ps. Getting three more orders of magnitude out of modern electronics is a tall order.

Measuring distance with sonic time of flight, on the other hand, sounds feasible with modern electronics. Generally, resolving things like this is performed with a pulsating or sinusoidal transmission and synchronous detection, which greatly reduces the need for fast electronics or transducers. The timings involved for sound are on the order of 3ns per µm (6 orders of magnitude slower than light); allowing 3ns to be 1/100 of a cycle gives a cycle frequency of 300ns (300kHz), which seems like it might be doable. Besides appropriate transducers, complications would include speed variance with temperature and pressure, multipath interference, interference from previous signals (some might call it inter-symbol interference), and clock variations.

Measuring distance with light intensity is relatively easy, but when you want 1µm of resolution that gets weird too. LED brightness may vary with power supply variations, temperature, and age; the receiver will also experience similar variations. Resolving distance variations relies on the amount of light being received, which depends on how much and how evenly the transmitter spreads its light. It also depends heavily on the alignment between sender and receiver, requiring a very solid mechanical structure.

If it comes to controlling the two sides to be so well mechanically coupled anyway, you might as well use a construct like what a digital caliper uses. Digital calipers use magnetic strips with tiny sensors in close proximity, and as the magnetic strip slides the sensor senses magnetic changes—this might be called a magnetic linear encoder. Other options include LVDT's and optical linear encoders (with some form of interpolation to get the fine resolution).

 

[mtwieg]

Hi All. My first post here so please go easy!

I need to design a cheap simple device to measure distance variations. The key being the word variation.... which will be from 0 to 5mm with accuracy/rsolution to a micron (10^-6m)

Having looked at some historic posts using IR, UV led with sensor is a good option. my proposed design will be telescopic with the sensor facing the led so no concerns about reflection properties. Also, the sensor and the led can be up to 150mm apart (or a bit more if it helps). Unit can be closed so no external light interference.

Measurement can be of light intensity or more involved circuitry to measure timing differences of signal.

I would prefer not to use an interferometer which will be too sensitive, pricey and too fiddly to set up.

What I havent found on other posts is the resolution and accuracy that can be expected from the LED route.

Any information and/or ideas that you have will be greatly appreciated.

[edit] I have considered hamamatsu PSD's but have no infor on cost]
Thanks

Fine distance measurement can be done optically, but it's a lot more than just an LED and a photodetector. Doing time of flight measurements over millimeter distances isn't feasible, but phase measurements are. One straightforward measurement is to have a circularly polarized light source on one end, on on the other you have a linear polarized filter and detector. As distance varies, the light intensity received will vary according to cos(4π*dx/λ), giving you submicron resolution easily. However, this measurement gives no reading of absolute displacement (without a precalibration).

 

[jiripolivka]

Fine distance measurement can be done optically, but it's a lot more than just an LED and a photodetector. Doing time of flight measurements over millimeter distances isn't feasible, but phase measurements are. One straightforward measurement is to have a circularly polarized light source on one end, on on the other you have a linear polarized filter and detector. As distance varies, the light intensity received will vary according to cos(4π*dx/λ), giving you submicron resolution easily. However, this measurement gives no reading of absolute displacement (without a precalibration).

The easiest way to measure 0-5 mm distance is to use an electromagnetic sensor, like that used in "digital" calipers or micrometer gauges.
If you cannot mechanically touch the distant object, look on KEYENCE laser micrometers. I used some for distances from 0 to 100 mm, and the reading resolution was better than one micrometer. Such devices use a trigonometer sensor projecting reflected light spot on an array of photodiodes. Varying distance of reflecting object caused different photodiodes along the linear array to be hit.

I used a simple light-intensity sensor for 0-30 mm distance measurement. A LED and a photodiode, and a small mirror attached to a moving object. After calibration I could read better than 10 micrometer resolution. Ambient light can be a problem.

 

[phongphanp]

T=0.693*R*C for single excitation , by this one ,T vary on R and C value only for the distance measure LED application.

The constant 0.693/λ is statistical datum of half life , I(d²) ≈ ∫(((hγ√(N-No)²)÷/(c•λ))d(d²) ...candela. , the scientist like to find the source. Doctors is not but macro phenomenon for him. In the shed-light world.c
Engineer will survey the configuration in the imitation world. The price of LED is low because high production/year.

Try Image processing book but more elaborate more expansive !!! :shock:

 

[phongphanp]

In the specify work , IR or UV , There two frame work that I know...
1. Chemical control Process
2. Electronics Control of instrument

Nowadays, Software Process is role on very much like the effect on Photoshop. And data sets on market were over the world to be select & buy.

 

[China-transformer]

A novice in the art of transformer design usually needs some guidance in making an initial estimate of the core size appropriate for the application requirements. One widely used method, with many variations, is based on the core Area Product, obtained by multiplying the core magnetic cross-section area by the window area available for the winding
There are many variables involved in estimating the appropriate core size. Core power handling capability does not scale linearly with area product or with core volume. A larger transformer must operate at a lower power density because heat dissipating surface area increases less than heat-producing volume.The thermal environment is difficult to evaluate accurately, whether by forced air or natural convection.Some core manufacturers no longer provide are a product information on their data sheets, often substituting their own methodology to make an initial core size choice for various applications.The following formula provides a crude indication of the area product required:
Where:
PO = Power Output
∆B= Flux density swing,Tesla
fT = Transformer operating frequency
K= .014 (Forward converter,PPCT)= .017 (Bridge, half bridge)

This formula is based on current density of 420A/cm2 in the windings, and assumes a window utilization of 40% copper. At low frequencies, the flux swing is limited by saturation, but above 50kHz(ferrite), ∆B is usually limited by core losses. Use the∆B value that results in a core loss of 100mW/cm3 (2times the “flux density” given in the core loss curves).These initial estimates of core size are not very accurate, but they do reduce the number of trial solutions that might otherwise be required. In the final analysis, the validity of the design should be checked with a prototype transformer operated in the circuit and the environment of the application, with the hot spot temperature rise measured by means of a thermocouple cemented to the center of the center post.

 

[phongphanp]

Somebody may use Matlab:simulink or Pspice (Must read all manual) to suspect the science phenomenon in LED&Magnet in Power Transformer . LabView have good/many panel and CFD program that for graphics display.

For LED, Vd = (0.693*ln(e^-(j÷2)*3nRT))÷d .

 

[betwixt]

There is another method not mentioned yet, microwave reflectometry. It isn't anywhere near as complicated as it sounds. All you need is a Gunn effect diode and a mixer diode inside a cavity. The cavity has a hole on the side facing the measurement surface from which low power microwave signals (< 1mW) emerge when the signal hits the target, some bounces back and re-enters the cavity. The mixer diode sees both the original signal and reflected signal which will add or subtract in phase depending on the distance between the cavity and target. The output current is proportional to the distance.

I use this system 'in reverse' to calibrate microwave oscillators. The signal is bounced off a known distance (about 5cm) and the oscillator tuned for a dip in mixer current.

It similar to the method used in speed radar traps although in that case the rate of change in mixer current is proportional the speed the target moves.

Brian.

 

[phongphanp]

Hi,

What's the subject name to learn radar method that you post, betwixt , i never learn that equipments. Because my country law that not over 10 watts for transmition .

 

[betwixt]

The speed radar system uses Doppler shiift and the ripple in mixer current is proportional to the speed of the object causing the reflection. In this case it isn't the ripple but the absolute value that is important. The mixer current gets an additive and subtractive wave peak at a distance of (wavelength / 2) so when the wavelength is short, even a tiny change in distance causes a significant change in current. For example, a 24GHz Gunn oscillator has a wavelength of about 12.5mm.

The power used in my measurements is very small, typically 1mW and the mixer current peaks at about 200uA. I'm not sure what power a speed radar uses but I would guess in the region of 200mW to give a range of a few hundered metres.

Brian.

 

[phongphanp]

Try to buy good meter nowadays in market have RF , IR support, I had heard about UV light led but not used . The other say it's green , may be more versatile in Image Processing curriculum. There many work such as on choice speed or velocity . The micro metes is spectroscopy technic, using has play role on science than engineer , present day, I think that in the last end of "computerize era".

https://en.wikipedia.org/wiki/Interferometry
https://en.wikipedia.org/wiki/Michelson_interferometer


You may build the size measure equipment ,too. !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[phongphanp]

Another form of LED formular :

∫ Vd d(t) = ∫ (0.693*√(ln^(e^(-j*(3/2)*^(e^σbeta(t))*N*kB*T)))/d)d(d) ; d(t)=vt .

And


I(total) ≈ ∫∫(((hγN√(N-No)²)÷(c•λ))d(x)d ...candela.

When you try to simulate/test in electronics lab , you should define more than 2 times of distance to get power range of echo signal . And try WolfameAlpha web , https://www.wolframalpha.com/ for solve above equations.


Hope this helps,

Phongphan Porana. :-x

 

[phongphanp]

You must make data normal distribution in f(x,y) form to integration . If you have talent on mathematics , try approximate N distribution. Very hard , it's logo of Matlab program so you may try by C language . :???:

 

[phongphanp]

Above equation have some error on finding Vd , omit symbol ^ in front of Beta decay . This is simple version of that V,I calculation(For convenient) such as no the geometry consideration , I had found in technical paper. But precise usage need collect statistical datum and testing in laboratory&Field . For university , I think using Finite Mathematics , FEM is standard . :-o

 

[phongphanp]

Someone may try to hand calculation of my above equations , and with numerical for variation too.

 

[jiripolivka]

Someone may try to hand calculation of my above equations , and with numerical for variation too.

From all above I can see that your original inquiry, how to measure a distance up to 15 cm grew up to a huge variety of problems. Maybe you should choose one solution and try it...
I still recommend Keyence micrometers as the best professional solution.

 

[FvM]

I don't see how the formulas should be related to the original question of µm distance measurement.

 

[phongphanp]

the valiable,n is atomic number and N is mole number.

refer, https://en.wikipedia.org/wiki/Atom_number
https://en.wikipedia.org/wiki/Periodic_table

I think that this size of atom is small enough for the micro meter.

 

[phongphanp]

Above equation have some error on finding Vd , omit symbol ^ in front of Beta decay . This is simple version of that V,I calculation(For convenient) such as no the geometry consideration , I had found in technical paper. But precise usage need collect statistical datum and testing in laboratory&Field . For university , I think using Finite Mathematics , FEM is standard . :-o

For the cm distance measurement, I had heard about sound sensor be used so much , many pople had buy electronics then testing and found poor quality should read datasheet of that qulity has depend on the number of pages and the inspirtion of people in the world and of own.