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I am looking for recommendations for a cheap (~$20) force sensor that can handle up to 10kN in one direction.

I've looked at a few, but most components saturate at about 100-1kN.

EDIT:

For the application I am looking at, it would require a polymer film type sensor (e.g ~0.5mm thick)

The application will monitor (and I use the word lightly), "impulse" forces. So large forces for very short contact times (0.1s - 1s). I realize this would probably put this kind of sensor into a precision component category, but hoping for some unique solutions =)

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  • \$\begingroup\$ Omega Engineering makes a good variety of load cells. But they have sensors only up to 4.5kN \$\endgroup\$ Aug 23, 2012 at 7:42
  • \$\begingroup\$ You'll have to define "cheap". In the range you need cheap is a relative concept. \$\endgroup\$
    – stevenvh
    Aug 23, 2012 at 7:46
  • \$\begingroup\$ Have you considered a mechanical linkage to reduce the applicable force, such as a lever? \$\endgroup\$
    – pjc50
    Aug 23, 2012 at 9:55
  • \$\begingroup\$ no I haven't pjc50, but I will give it a think. Thanks =) \$\endgroup\$
    – nehz
    Aug 23, 2012 at 15:06

4 Answers 4

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10kN is a very large load (a metric tonne). I don't know of any commercial load sensors which can take that load and come in at under $20. (unless you get a second hand one that's rubbish).

Here's my suggestion:

IR Transceiver

Optical transceiver: These can be used to measure the very small movements as a load causes something to flex. Stick a white piece of paper to the back of a rectangular metal bar. You need to spec this bar so that it moves a little less than 1mm when it's under 10kN load. Mount the transceiver about 1mm from the paper. Adjust the LED current so that you get a high reading.

Load sensor

This is a very rough diagram of how it's set up. The scale is all wrong. But you can see that the sensor is set up so that any bend in the metal bar closes the gap between the bar and the sensor.

Other things you'll need are: A way to prevent ambient light reaching the sensor, something to prevent the metal bar crushing the sensor if you place 6 tonnes on the scales.

Pros: easy and cheap to make. Very sensitive. Cons: It's temperature sensitive (like many things), so you'll need to use software to tell the difference between load and temperature. Like kitchen scales, you can simply tare the sensor. Take a reading with no load, then take a reading with the load. Subtract the readings.

Alternatively, use two other IR transceivers as voltage references. Set up one to have maximum light reflected back into it. Set up the other so that no light is reflected back into it. Now use these as the Higher and Lower voltage references in your ADC.

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This Kistler sensor is available in different ranges, including 0.. 10 kN

enter image description here

edit after your price indication
Hm, 20 dollar for a 10 kN sensor is a tall order, or rather, not a tall order :-). Anyway you know what I mean. I'm not sure you'll find anything at that price.


Kistler website

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  • \$\begingroup\$ yeah I thought so too... just chucking it out there incase something exists :) \$\endgroup\$
    – nehz
    Aug 23, 2012 at 12:59
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Depending on exactly what you're trying to measure, you might just be able to glue a resistive strain gage (or two, or four) -- http://www.omega.com/toc_asp/subsectionSC.asp?subsection=E02&book=Pressure -- to your mechanical structure and wire them up in a Wheatstone Bridge configuration. They run about $12-$15 each, available in packs of 5, though. You'd need to wire up your bridge to an instrumentation amp (about $6), and maybe include a trim pot.

The more active sensors, the more sensitive and temp compensated your configuration will be. Even with one, output will be linear with strain.

These can be tricky to mount. Unless you're pretty good with an iron, you probably want to order them prewired. If you anticipate long cables, order them with three or four wires, so you can use a feedback circuit to keep the excitation voltage for your bridge constant.

You might come in slightly below the cheapest on load cells in cost, but the load cell will be your most care-free approach.

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I just had a relook at force resistor sensors and it seems like I missed look the spec sheets: http://www.tekscan.com/flexible-force-sensors

Seems like you can adjust the circuit to get your desired sensitivity range. They are not as precise as your strain guage or load cell, but it seems to be promising..

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