FlexiForce™ FAQ

Environmental
Using a Puck or Shim
Conditioning
ELF System and Calibration
Other

Environmental

What are the influences of humidity on the FlexiForce sensor?

As far as we know, sensors can handle humidity but not water saturation/submersion. They are not considered to be waterproof, even though the outer material (mylar) is. One reason is that the connector/tab area has an opening for connection of the traces.

What are the influences of electro-magnetic radiation?

From what we have heard from customers who use the sensors around magnetic fields, there is little or no effect. We do not know what would be the response of the ink around radiation.

What are the influences of tube-lights around the SSB?

Depends on the temperature the lights are exuding. Sensors can handle up to about 180 degrees in some cases, but 165 degrees is the maximum recommended. See data sheets.

Can the sensors pick up electrical noise?

Yes, to a small degree. We have designed the sensor with both traces to one side of the sensor so there is minute amount of space through which noise can travel.

Using a Puck or Shim

What is a puck/shim?

A puck/shim is an object that is used between sensing area (button) and load that serves as a funnel for a load that is too large (portion outside sensing area), or as an enlarger for a load that is too small (less than 70% of sensing area, or area of less than 0.077 square inches).

What size puck should I be using?

Must be between 70% (0.2625 inches / 6.67 mm) and 100% of sensing area diameter.

What material must be used? e.g. plain steel, hardened steel, plastic, something else?

Plastic is best. Rubber is more sensitive than plastic, and steel is less.

What is the maximum roughness of the surface?

We wouldn't use something like a cheese-grater surface because it will puncture the sensor. Smooth bumps are best. Sandpaper surface is questionable...should be fine as long as there is no shearing/sliding.

Do I always have to use a puck?

If the load you are measuring is made of a hard material, like metal, using a plastic puck would give more accurate readings. Also, if your load is too big, use a puck to capture the load that falls outside of the sensing area. If load is less than 70% in size (e.g. a pen point) than sensing area, you need to use puck so PSI is lower.

What should be at the back of the SSB: 2nd puck, a flat surface larger than the SSB, something else?

A flat surface is best. Materials can make a difference on output, see above.

Conditioning

Why do you need to condition the FlexiForce sensor? What is the reason for that?

Breaking it in. This conditions contacting surfaces of the ink, which will improve performance and repeatability.

How incorrect are the values if the sensor is not conditioned?

Could be greater than standard ± 5% error.

What do you mean with "stabilized"? Is the resistance constant, or is it decreasing with a constant value?

The inks are resistive: the greater the constant force, the less the resistance.

Can you give me an estimation of the time it takes to stabilize?

2-3 seconds for constant load. If using 'spongy' load, could take 10 seconds.

How long must the sensor be unloaded before you load it again?

Imagine tapping your fingers or typing. Time between can be short...no exact time. Calibrate in time frames you will be using when testing/measuring.

Is 110% the maximum load the sensor can handle?

This is the weight you should apply when conditioning the sensor, 110% of the maximum load you will be measuring. That way you get higher resolution around the load with which you will measuring.

What is the maximum period of not using the sensor before you have to recondition it?

Recondition the sensor every month, if haven't used it for that long. Store your sensors in recommended, protected environment.

ELF System and Calibration

What is the lowest force reading that the ELF System will give?

30 grams / 0.066 lbs.

What is the speed of the ELF System?

200 Hertz

Can I use more than one sensor at a time?

The current system electronics allow for 1 sensor input at a time, but you could use multiple ELF systems hooked up to a serial port adapter. You would need to run a separate instance of the ELF software for each sensor. (requires 2.01 patch)

What is the reason for calibrating the sensor?

Calibrating allows you to: adjust the gain/sensitivity of each sensor and select unit of measure (grams, pounds, newtons, etc.) by converting raw percentage units to calibrated units. If you use the sensor without calibrating it, the data you get shows as a percentage of the maximum range of the sensor. Furthermore, there is variance between sensor runs, which could give different resistance values when applying the same load if not calibrated prior to testing.

Do I have to calibrate in test environment?

You should calibrate as you would test: use same load weights and materials, temperature and time intervals.

110% of the test weight: Is this the weight you expect that will be applied to the sensor when you are measuring?

No, you should calibrate to 110% of the test load so the sensor and system shorten the force range to give greater resolution. This is the same as adjusting the gain/sensitivity of the sensor.

Other

What is the resistance of the FlexiForce sensor?

At no load, the resistance is 5M Ohms. At full load, it is 20k Ohms.

Can I adhere the load to the sensor or the sensor to a surface?

If you need to adhere the sensor to a surface, apply the adhesive to the shaft of the sensor, not to the sensing area. We wouldn't recommend adhering the load to the sensor because any adhesive can apply a load. Also, an adhesive (e.g. glue) could make the load uneven.

What is the "life" of a FlexiForce sensor?

The durablity of the FlexiForce sensor depends on the conditions to which it is exposed: magnitude of the load, the interface material, and the direction of the load (minimize shear). Under "normal" limits, the sensor typically can perform up to 1,000,000 cycles/applied loads. Our tests were performed by applying a 50 lb. impact load on the sensor, which was between two pieces of metal.