How to measure distance between two sensors

Started by hassan_alsamahi 6 years ago8 replieslatest reply 6 years ago5838 views

Hello everyone, I'd like to ask a question related to sensors, is there any sensors that can measure the distance between each other relative to each other, for instance I have a this sensor on point A, and another one on Point B, how to read the distance or the position of the sensor B, relative to Sensor A in the 3D space??

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Reply by antedeluvianSeptember 3, 2018

 You may want to look into "time of flight" sensors as one option. AMS have one that they claim measures distances and I know ST make some as well.

Some process control equipment manufacturers also make complete systems like this on from Pepperl + Fuchs.

There are some ultrasonic types that are used in tapeless tape measures

There are radar and lidar techniques.

Not to mention lasers.

The distances themselves can play a role in the technology selected and your level of interest. 

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Reply by CustomSargeSeptember 3, 2018

Distance is straightforward, many methods.

Range and resolution will dictate method effectivity.

Wide range may warrant multiple methods 

3D space relative position is a completely different can of worms.

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Reply by Bob11September 3, 2018

You need to provide more information about the application. Do you just need distance (a scalar), or full 3D position (a vector)? At what distance (inches or miles)?

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Reply by hassan_alsamahiSeptember 3, 2018

I want a sensor that reads the position of another sensor (the same type) in a 3D space (xyz vectors), and measures the resultant distance between the sensor and itself. for instance, sensor A will be at its default position which is (0,0,0), and another sensor B, is at position (2,3,5) relative to sensor A, in other words sensor B is 2 cms away in the x-axis of sensor A, 3 cms away in y-axis, and 5 cms away in z-axis. So sensor A detects any movement of sensor B relative to itself....did you get it? 

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Reply by Bob11September 3, 2018

That's a tough nut to crack. If there were (inexpensive) sensors that did that you'd almost certainly find them in the gaming industry (Kinect, etc.) There are companies that sell much higher cost equipment of that sort for medical robotics and the like, for example, check out https://www.ascension-tech.com/.

Game systems tend to use vision tracking, which isn't what you are looking for. At the small distances you mention GPS doesn't work. You could use MEMS accelerometers reporting via WiFi, but that will drift off and have calibration issues. Another option is a third 'base station' in the vicinity of A and B that uses some of the methods mentioned by antedeluvian above to track A and B together. The exact application will tend to determine which technologies are feasible and which aren't. I'm not aware of any off-the-shelf sensor technology capable of that sort of 6 DOF position reporting at those distances. 

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Reply by martin_harnevieSeptember 3, 2018

Very rough measurements you can do if the radio has RSS or signal quality capability, but it will not be anywhere near the resolution you're indicating.

Furthermore it will be consuming a lot of battery which severely limits the frequency of such measurements for any practical battery life.

If the challenge is real time updates during short intervals (~minutes), you might be better off using dead reckoning. 

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Reply by s-lightSeptember 3, 2018

i don't know if my ideas are possible - but thought i just write down what came to my mind...

eventually you could work with some sort of Electro-Magnetic Resonance or inductive or capacitive or similar things - like pen-tablets (wacom and co..)

i don't think that this gets easy...
but eventually its a direction to search...

on simple diy arduino example of general '3d' capacitive detection (with a static 'big' sensor area and a finger as the moving object that i found some time ago is this instructable

other 'similar' 2D applications is a Theremin

now you know just my thought and ideas that came to my mind ;-)

sunny greetings


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Reply by kevboSeptember 3, 2018

One way of doing this is with microphones.   Your target needs a speaker that creates a click, then 4-5* microphones spread around your space measure when the click arrives.  The difference in time of arrival can be resolved to a position using similar math as GPS.   You need to account for variations in speed of sound. (SOS)  This can be done with a separate click generator and mic that are mounted with a fixed separation on each side of the space.  If moderate accuracy is acceptable, you can just measure temperature and calculate approximate SOS from that.

*You need an extra mic if the speaker is not under control of the timing electronics...if you know when the click (t=0) was emitted, you can do with one less mic.  Depending on situation, the speaker might need to be battery powered and not wired. Adding a mic is probably easier that adding a wireless link to the speaker.

This only works if the space is reasonably quiet or you can make very loud clicks...though you can probably use correlation techniques to find the desired signal in some noise.  Also the space needs to be fairly uniform and filled with something that conducts sound...it won't work in space, or if the temperature or gas mix is stratified...like if there is a significant thermal source in one part of the space, or SF6 pooling at the bottom. Also sound reflective items and surfaces can be problematic..."echo-y" spaces are bad.

I was involved in a project that used this technique to determine the path of (supersonic) bullets passing over the mics. Instead of a click from a speaker, the mics were picking up the shock wave (sonic boom) of the bullets.