FSR Data Sheet

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What's An FSR?

The Force Sensing Resistor™ is a polymer thick film (PTF) device which exhibits a decrease in resistance with any increase in force applied to the active surface.  Its force sensitivity is optimized for use in human touch control of electronic devices.   The FSR is not a load cell or strain gauge.  Though it has similar properties, it is not suited for precision equipment.

Force (grams) vs. Resistance

Figure 1 -- Force vs. Resistance

The FSR force vs. resistance characteristic shown in Figure 1 provides an overview of the FSR's typical response behavior.  For interpretational convenience, the force vs. resistance data are plotted on a log/log format.  These data are representative of our typical devices, with this particular force vs. resistance characteristic being the response of standard part #152 (1.27cm diameter circle) with a 0.6mm thick silicone rubber (50 durometer) overlay and using a 0.56 cm diameter flat probe for actuation.  In general, the FSR's response approximately follows a power-law characteristic.

At the low force end of the force-resistance characteristic a switch-like response is evident.  This threshold, or "break force", that swings the resistance from greater than 1Mohm to about 50-100 kohm (the beginning of the power-law) is controlled by the top substrate material and overlay thickness and flexibility.  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.

Force (grams) vs. Conductance

Figure 2 -- Force vs. Conductance

In Figure 2, force vs. conductance (1/resistance) is shown.  This format allows simpler interpretation on a linear scale.  Notice that the response is in the range of 0-2kg, which is common to human interface applications, is very linear.  A simple circuit called a current-to-voltage converter (see TechNote; Suggested Interfaces 1-7) takes advantage of this inverse proportionality and can be useful where response linearity is desired.

FSR™ Technical Specifications
These are typical parameters.  FSR's are custom devices and can be made for use outside these specifications.  Consult Applications Engineering with your specific requirements.
Simple FSRs and Arrays
Parameter Value Conditions
Size Range Max = 20" x 30" (51 x 76 cm)
Min = 0.2" x 0.2" (0.5 x 0.5 cm)
Any shape
Device Thickness 0.008" to 0.050"
(0.20 to 1.25 mm)
Force Sensitivity Range 30g to 10kg  
Pressure Sensitivity Range 0.45psi to 150psi
(0.03 kg/cm2 to 10 kg kg/cm2)
30g to 10kg
1 cm2 actuator
Part to Part Force Repeatability ± 15% full scale For typical part with consistent actuation
Single Part Force Repeatability ± 2% full scale  
Force Resolution Better than 0.5% full scale  
Break Force 30 to 100g (1 to 3.5 oz) typical Dependent on probe size/shape
Stand-Off Resistance > 1Mohm  
Switch Characteristic Essentially zero travel  
Device Rise Time 1-2msec (mechanical)  
Lifetime >10 million actuations  
Use Temperature -30șC to 170șC High temperature adhesives
Maximum Current 1 mA/cm2 of applied force  
Sensitivity to Noise/Vibration Not significantly affected  
EMI/ESD Passive device -- not damaged by EMI or ESD  
Lead Attachment Standard flex circuit techniques See TechNote

Comments?   Email me at crwillis@androidworld.com