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Load Cell/ Sensor Recommendations for Weight Shift Detection

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Hi all,

I have a project for a medical device that is to detect when weight shift occurs from right to left foot and from heel to toe of each foot. I only need relative load (e.g. right foot bearing 70% load, left foot 30%) so the high precision of a load cell or strain gauge is not needed, which is why I was leaning towards FSR sensors. Off the shelf have very poor repeatability from sensor to sensor and require calibration. The most important aspect for the selected sensor to have is that is is ready to integrate to our PLC system without needing individual in-house calibration and signal conditioning.

I have gotten quotes for some custom FSRs with PCB boards for signal condition included and ready for integration with my +/-10V analog input module for my PLC, however these seem pretty pricey. Does anyone know of alternatives or where to find low-cost load cells? The initial research I have done seems pricey also and I don't need the precision or complexity of these sensors, but I'm curious if this will be cheaper. The issue I see with any sensor is that they will require calibration for repeatability as I will be using 4 per machine, unless these load cells have relatively high repeatability from one sensor to another right out of the box (FSRs can have up to 40% variation from one bath to another which is why I would need signal conditioning and calibration). Any advice would be appreciated.

I would advise against using the FSR sensor because of their lack of stability and matching. What you save in sensor cost you will more than spend in chasing stability and accuracy which you might never achieve. Go with something like, just an example: https://www.sparkfun.com/products/14282
a  200kg load cell and just accept the sensor cost, far more stable, repeatable and comparable, you will end up with a better solution. I don't know if that sensor is suitable but something of the sort. As they say, we don't need to reinvent the wheel. :)

Totally agree with the previous reply.
To detect heel to toe shift you will need quite a good signal which FSR are not going to give you. Too much drift.

You could go for an analog sensor then use PLC weighing modules or directly buy a 10V sensor.

--- Quote from: am1 on February 26, 2024, 06:08:36 pm ---where to find low-cost load cells?

--- End quote ---

Sellers : Scaime, Dini Argeo, HBM, Flintec, Arpege Master K, Mettler Toledo, Precia Molen

These are industry oriented, maybe they have cheap sensors that would meet your requirements.

Just be aware that is you go for 4 sensors the total weight of the person is divided by 4 on each loadcell. So you would not need a 200kg sensor x4, maybe a 100kg would be enought, just try to estimate the structural weight.
You will also need some filters as depending on the physical condition of the person they might not be able to stay stable enought.

Industrial type load cells will be relatively expensive, but the type used on person weighing scales are very cheap and easily available. They cost less then EUR1 and usually just have a half bride configuration.

Even if the load is ideally shared between the 4 sensors, the worst case load can still be mostly on one sensor. In addition to the weight there can be some dynamic load, accelerating the body when taking a step off the sensors.  So a 200 kg range can well make sense.


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