Searching a force sensor

[pmb]

Hi!
I'm searching a force sensor for medical purpose. I want to put the sensor under a patient when a CPR (Cardiopulmonary resuscitation) are performed on him. So I have the choice between the FSR 402 or the FlexiForce A201. But the sensor has to be able to measure a force of 250 lbs.
I would rather take the FSR because of the price but I am not sure if it can handle that weigth.

[adafruit_support_bill]

But the sensor has to be able to measure a force of 250 lbs.

Are you talking about the total force applied to the patient? These are fairly small sensors and the force will be spread out over an area much larger than the sensor. Unless you design a mechanical means to transfer 100% of that force onto the sensor (less than 1/3 square inch) the actual pressure seen by the sensor will be much less.

250 pounds applied 100% to the sensor would mean a pressure of 750 Pounds per square inch.
The FSR-402 is rated for 22 pounds of force which would be ~66 psi.

[pmb]

Thanks for your reply!
250 lbs would be the maximum force applied. Also I think I will use 4 sensors to measure the force applied. But the mean force would be about 100 lbs.

[adafruit_support_bill]

Also I think I will use 4 sensors to measure the force applied.

That sounds like a good idea. You might also consider using 4 of the .FSR-406 sensors. These have a larger surface area.

[Zener]

I would think you would want a rigid board with the sensors under that. The problem I have had with FSR's is the steady state resistance can drift. The varying weight of the patient could throw it off. Another way to say it is they don't have great dynamic range. You might try adapting an electronic bathroom scale. I think I remember seeing a thread about that a while ago.