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I've got just a simple question. What happens when I overload Force Sensitive Resistor (FSR). Example Here.

FSR

Let's say that it's got force sensitive range between 100g and 10 000g. What would happen if I'd create pressure about 100kg? I see that resistance is decreasing with bigger pressure. Will there be almost 0 ohm resistance? If so, can this FSR survive this overload? Has somebody test that?

Thank you for any answer.

  • It depends a lot on how it is mechanically set under pressure. The backside has to be against a very flat surface and the pressure has to be applied evenly spread over the whole sensor. That is hard to achieve, so the mechanical stress damages it. I did not test it, but I suppose it can handle a lot more than the 10kg, but it will get damaged. I think that it is impossible to get to almost zero ohms. There are other materials, for example conductive rubber, that can handle someone standing on it. – Jot Sep 8 '17 at 8:45
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    Also asked at forum.arduino.cc/index.php?topic=499102 – per1234 Sep 8 '17 at 9:29
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I see that resistance is decreasing with bigger pressure. Will there be almost 0 ohm resistance?

The harder the force, the lower the resistance. Sparkfun has a datasheet attached that shows the following graph:
FSR Graph
Notice how both axis of the graph are logrithmic. This means that the resistance will never reach 0 ohms. However it will get close. At 10 Kg (22 lb) the resistance is about 250 ohms.

What would happen if I'd create pressure about 100kg?

The datasheet has the following to say for weight above the 10 Kg mark:

At the high force end of the dynamic range, the response deviates from the power-law behavior, and eventually saturates to a point where increases in force yield little or no decrease in resistance. Under these conditions of Figure 2 [ie. the graph above], this saturation force is beyond 10 kg. The saturation point is more a function of pressure than force. The saturation pressure of a typical FSR is on the order of 100 to 200 psi. For the data shown in Figures 2, 3 and 4, the actual measured pressure range is 0 to 175 psi (0 to 22 lbs applied over 0.125 in^2). Forces higher than the saturation force can be measured by spreading the force over a greater area; the overall pressure is then kept below the saturation point, and dynamic response is maintained. However, the converse of this effect is also true, smaller actuators will saturate FSRs earlier in the dynamic range, since the saturation point is reached at a lower force.

In summary, the weight applied can go over 10 Kg providing that weight is spread over the sensing area. The larger FSRs (such as this one) are better suited for this purpose as they have a larger area for which to spread the pressure.

Note: It is quite possible that with 100 Kg you could irreversibly damage the FSR, particularly if the weight isn't spread over the sensor area.

Measuring an analog voltage from the sensor is possible so that it can be fed into one of the analog pins of the Arduino. This Adafruit page has a nice table at the bottom showing the analog voltage that you get when you put the sensor in a voltage divider network (ie. in series) with a 10K ohm resistor.

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