Cheap displacment sensor, please help

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Sully1071

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Im looking to find the cheapest possible mean of finding position along a 1metre long slider. I have looked at using draw wire transducers but they seem very expensive. I just want a a sensor that will give me position and i can plot against time to find velocity.

Any help is appreciated. Thanks
 
Define inexpensive as my inexpensive may not be the same as your inexpensive. Also you make no mention of the uncertainty?

The cheapest way I can think of is using a 10 turn (or more) pot and fabricate your own string pot circuit.

Ron
 
I suggest to use constantan wire of 0.1mm diameter.

It has a resistance of 62.4Ω/m and a temperature coefficient of -0.8% at 100°C temperature difference. Maximum allowable temperature is 600°C.

You could use it along your slider and use a beryllium-copper contactor as wiper along the wire.

One spool of 1,430m length costs $22.83 at https://www.reichelt.de. Order number is RD 100/0,10.

Currency calculation is based on $1.3 for one €. Sales tax for overseas delivery has been subtracted. (Reichelt price is €20.90 incl. 19% sales tax )

Boncuk
 
Cheap is less than 100 euro roughly. Its for a project but as i study mechanical engineering i dont have the best know ledge of electronic systems.
 
If your slider is being driven by a runner on a rotating threaded shaft you can simply count the shaft rotations.
 
What's the output intended to feed? Does it need to be analog? If digital, does it need to be bidirectional? I'm thinking maybe a quadrature encoder with a wheel rolling against the frame.

Ken
 
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am im not very knowledgeable about sensors and that area. i will want to calculate velocity by plotting the displacement vs. time, and so will be doing so labview or another program. Analogue or digital i dint know.

I only want to measure the displacent in the forward push.
 
You have a few things to consider, I liked the suggestions of Boncuk and KMoffett. Also, the final chosen method will depend on the velocity involved. The actual anticipated velocity is a big key player factor. Then the matter of the actual setup. I use string pots in many applications but also use LASER systems in others where a string pot would not be fast enough. Some solutions can be inexpensive while some are quite expensive.

Ron
 
At the top of the vertical frame you have rotary motion. Attach a rotary potentiometer at that point.

pilko
 

Hi Ron,

this "Hades-machine" (Hades = Greek translation for Hell ) trains the bizeps muscles, and nothing else.

May be the ex-governator of Califonia, Mr. Arnold Schwarzenegger is able to push up the heavy weights at high speed, thus requiring full stroke of the push bar.

62.4Ω per meter of the suggested constantan wire can be used for a voltage divider and following amplifier with an output either connected to a microcontroller's ADC to digitally indicate stroke in meters or percent.

A cheaper solution would be an analog voltmeter at full range of the amplifier's output.

That's the solution I'd choose for that kind of toy.

Regards

Hans
 

Not sure what the OP's accuracy requirements are, but the "crankshaft" linear-to-rotary linkage will not give a linear output from the pot/encoder with linear motion of the subject. More like a trig function I think.

Ken
 
Having seen a pic of the slider I'm with Pilko. Use a simple rotary pot on the axis at the top of the frame.
 
i cant affect the machine structurally so cant attach a potentiometer at the rotating shaft as it sits in bearings.

All string potentiometers seems to be costing €200 ++. Is that sounding accurate?
 
Hi Hans and how goes it.

I'll tell all what blew me away. I use quite a few motion encoders from for example BEI. Granted high end costing a few thousand USD. While the unit Ken linked to has a max of 360 PPR the 51 USD price is what literally got me.

Looking at the picture my choice would likely be a string pot. That would afford a nice linear voltage transition over the travel range. Should be easily mounted and set up as well as easy to chart. No clue what they would cost. I did have a 10K 7' (about 2 meters) one lying around I rescued when we went with newer models. Anyway, I would use a string pot if the budget allows.

Ron
 
Several years ago I needed a bunch of string pots that had to be cheap, because they would be potentially expendable...under a glacier. The cheapest I could find were from this company: https://www.spaceagecontrol.com/ They don't seem to have much specific data or pricing on their website, but you could contact them.

Ken
 
An accelerometer and integrate either in hardware or in code?

Advantages: cheap and a piece of cake to set up.

I figure I've done that with far less stroke at the same frequency in code and had it work out.

The key was it didn't need to be an absolute position to calculate speed or a good estimate of power or force given the known static forces and spring constants involved.
 
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