proximity sensor 1 mm accuracy

hello i'm looking for proximity sensor with 1 mm accuracy for my project, does anyone know what sensor should i use? :confused:

Over what sort of distance?
Contact / non-contact?
Dimensions of target?

Such sensors are easy to find, but how many $ are you willing to spend?

TheMemberFormerlyKnownAsAWOL:
Over what sort of distance?
Contact / non-contact?
Dimensions of target?

i need non-contact sensor, and i will use it to measure land subsidence do you have recomendation/reference?

jremington:
Such sensors are easy to find, but how many $ are you willing to spend?

my budget is around 40-100 US$ :slight_smile:

measure land subsidence

That sounds like quite a challenging project, as defining the "land surface" to 1 mm accuracy seems problematic.

How would you mount the sensor, supposing that the land is sinking?

A โ€˜sensorโ€™ needs to be fixed to something.

So if the land subsides wont the sensor subside as well ?

A very long pole?

jremington:
That sounds like quite a challenging project, as defining the "land surface" to 1 mm accuracy seems problematic.

How would you mount the sensor, supposing that the land is sinking?

my idea is the sensor will be mounted under a pipe, and the pipe's leg will be planted under ground

srnet:
A 'sensor' needs to be fixed to something.

So if the land subsides wont the sensor subside as well ?

yes the sensor needs to be fixed

Some decades ago Jerry Jennings and Tony Brink et al at my alma mater invented what became known as a "telescopic bench mark", see fig 7 here.

Their very purpose was to measure subsidence in dolomitic mining ground, where huge sinkholes that would swallow whole buildings would appear overnight. Turns out the sinkholes formed from the bottom up, so when the "crust" eventually fell in it looked as if a huge hole had formed in an instant.

So the TBM consisted of pipes grouted into the rock at various depths, and precision survey methods on the surface would keep track of the levels of the tops of the pipes. The inner pipe was the lowest indicator, so if a hole started developing way down deep, the inner pole would fall first.

That way, the growth of a sinkhole could be predicted from the inside out.

Perhaps you have something similar in mind, where it's the top of the pipes that need to be monitored?

So you stick a pipe into the ground as reference point for the sensor. Makes sense.

Now how are you planning to mount the sensor, so that it does not sink with the pipe when the ground subsides? Because then you still measure either nothing, or a wrong value!

Yeah I mentioned the tbm approach if the OP means to measure voids opening up as in sinkhole areas. Since there are many segments to a tbm, what you're looking for is relative movement rather than absolute, as when an inner pipe goes down due to a void forming, but the outer ones attached to higher strata stay still. In that case, the sensor could be mounted on the outer pipe, which will be ok until the day it disappears too in which case there will be a sinkhole that you will see from the moon.

But if it's non-catastrophic type subsidence, then I guess even as the 1965 paper said, precision survey of bench marks mounted in concrete blocks in the field of interest would be the way to go, even over 50y later? (It's a long time since I operated any survey gear, but even back then, sub-mm was doable with careful use of the better models of equipment and mathematical techniques to reduce the error in a closed loop.)

He could be measuring dirt rolling down a hill for all we know.

There's not much of an explanation!

Steve