Distance measuring circuit, rf or ultrasonic?

[fastline]

I need to measure distances where IR would not be possible. I need to measure approx from 20ft to 300ft accurately. I am trying to decide which would give the easiest circuit design and highest accuracy without interference? I plan to use a micro controller for the project.


Edit, to define accuracy, +/- 1" would be just fine. Possibly even a little looser would still work.

 

[jpanhalt]

Ultrasound will not be very accurate over that distance. It is influenced quite a bit by weather conditions. I would not rule out light. Stanley sell a series of laser-based instruments under its FatMax brand. This one will go to 600 ft.:
**broken link removed**

I believe the same or very similar units are available under other brands. I have the FatMax100 and can say it is quite accurate for my purposes. Of course, speed of light also varies with the medium, but not as much as ultrasound in air. Now, if you are under water...

John

 

[fastline]

I am basically trying to determine the depth of drilled holes on the earth that are not exactly straight. Laser just will not accurately find the depth. These are open air. I realize lowering a device in the hole might be the best way but faster and easier is what I need.

 

[jpanhalt]

If the hole is not straight such that you do not have line of sight, are you sure ultrasound will work any better? You will never get that accuracy with sound at 300ft.

John

 

[fastline]

I am interested to see what kind of resolution can be obtained at 300ft though. Maybe 6"?

Is RF line of sight only? Why is ultrasound preferred over RF? There should be some type of line of sight but protruding rocks, pipes, and such will be problematic. I know they use US today for doing similar testing but not at 300ft that I am aware of.

 

[magvitron]

I have an idea, you could use resonance for measuring the depth.? I know there will be some problems like resonating @ 1/4th 3/4th etc,.. but worth brain storming , I think.

 

[jpanhalt]

I am interested to see what kind of resolution can be obtained at 300ft though. Maybe 6"?

That specification isn't given in the advertisement. Did you try looking at the vendors site? Accuracy is stated as +/- 2mm at 200 m. That is not surprising when you consider the mechanism involved. (NB: Cannot post images form local PC yet.) How did you come up with +/- 6"?

Is RF line of sight only? Why is ultrasound preferred over RF? There should be some type of line of sight but protruding rocks, pipes, and such will be problematic. I know they use US today for doing similar testing but not at 300ft that I am aware of.

I never said or even suggested that ultrasound is preferred over RF. All the methods I have mentioned are based on reflections. Sure, there are ways to look at the echo spectrum from some methods and try to figure out what is going on, but I have the impression this was either a DIY project or something you need to buy at relatively low cost. The advantage the laser has over RF and sound is the beam is quite narrow, so it can be manipulated to avoid things that protrude from the walls. Also, you can see the red dot that is projected and determine exactly what you are measuring.

Is this something you really need to do , or just idle thinking about the challenge?

John

 

[fastline]

Thanks. This is certainly something that I need to do as a DIY project. I need it as a tool for business. I realize I might be able to find something similar in industry to buy but the point is to learn from the project as well.

I mention ultrasound as "preferred" only because in my research of RF, most people immediately just recommend ultrasound.

I DO agree though on the resonance and was exactly where I was going but really unsure how to set that up and what components I might use for that. It is almost like I need to run a sweep test and lock onto the max amplitude which sounds more complex than it needs to be. There is also the issue of not being able to see the bottom. Sometimes these holes are not very straight and can turn about 5*.

I am mostly trying to brain storm a technology that will both be relatively simple, and have decent accuracy in a range of conditions knowing that in all situations, the shaft will always be considered like an "unknown length of pipe". Some of these will even have water sitting in the bottom so it must be able to reflect accurately off of water.

 

[ericgibbs]

hi fastline,

The number of holes you actually want to measure could determine how much you want to spend on the project.?

Eric

 

[magvitron]

For an RF to be used in this project it cannot be in the UHF and higher, because its absorbed by water, and the metal pipe (I'm assuming metal) will reflect the RF radiation and may cause disruption of signal. Sound 'sounds' like a better option because its more manageable than the RF thingy.

 

[Nigel Goodwin]

For an RF to be used in this project it cannot be in the UHF and higher, because its absorbed by water, and the metal pipe (I'm assuming metal) will reflect the RF radiation and may cause disruption of signal. Sound 'sounds' like a better option because its more manageable than the RF thingy.

I don't quite see how anything is going to work when it's got to go round a bend?, the bend will be detected as the end of the pipe.

 

[cowboybob]

I am basically trying to determine the depth of drilled holes on the earth that are not exactly straight. Laser just will not accurately find the depth. These are open air. I realize lowering a device in the hole might be the best way but faster and easier is what I need.

If I may:
1. When these holes are drilled, is there some reason the depth isn't noted at that time? (Number of drill pipe sections or some other method of total drill + shaft length).
2. Are the holes all of the same diameter? If not:
3. If an object (say, 2" in diameter) were dropped down any one of these holes, would there be any obstructions that would prevent the object from reaching the bottom?

I have an idea in mind but I am unsure of it being a reasonable solution until I know the answers to the above.

Or, in other words, I don't want to sound dumb before this august group .

 

[user_88]

It would be interesting to try a pressure pulse ... maybe generated by an air tank opening a butterfly valve.
The relevant question would be whether the degree of amplitude attenuation of the pulse would be too great for the maximum distances that you require.
The implementation of a pressure pulse detector would be relatively simple, using a pressure transducer, and some means of determining the time interval between the initial and return pulse.
It would seem that an air pulse might be relatively immune to minor hole diameter anomalies ... This suggestion would be subject to some degree of experimentation.

The argument for an air pressure pulse, used as the interrogation signal, would be that the line of travel of the primary, or strongest pulse, would seem to be primarily restricted to the physical central axis of the hole. Straight down and straight back up. ... Whereas, RF or ultrasound waves might be subject to multiple reflections withing the test hole, causing inaccurate or non-reproducible results.

 

[fastline]

To try and answer some questions generally, these holes need filled, we have to record the depth and plugging methods. Fast is key. Holes can be cased in plastic or steel, or open earth. Many were test holes for various reasons.

I bought this cute little Arduino USF distance device to play with . I knew going in it did not have the power to do reach too far though. I was thinking about compression wave sensing but not really any real pressure. I just need a little hand held device. I know USF has been used for similar things. I am just realy unsure how to set that up, what parts to use, etc. Typically you would have a USF sounder and receiver of the same frequency. I am just cannot really find these devices anywhere and not yet sure what problems I would encounter. Technically with sound, it should go to the bottom regardless of straightness and return in the opposite sign.

I designed a branch resonator as an exhaust for momma's car with adjustable sections. Works perfect and I used a little packing to slow the waves a bit to act like a longer tube.

anyway, back to USF or relative methods. I just need to make sure what ever I do is the right move and not a waste of time.

 

[jpanhalt]

I DO agree though on the resonance and was exactly where I was going but really unsure how to set that up and what components I might use for that. It is almost like I need to run a sweep test and lock onto the max amplitude which sounds more complex than it needs to be. There is also the issue of not being able to see the bottom. Sometimes these holes are not very straight and can turn about 5*.

Won't resonance tell you how long the hole is, not how deep?

John

 

[fastline]

There is no real difference here. Long/deep.