Rubber Cord Stretch Sensor not as specified

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roy_s
 
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Rubber Cord Stretch Sensor not as specified

Post by roy_s »

On 11/15/14 I ordered (2) Conductive Rubber Cord Stretch Sensors. Both appear to be way out of specifications. At rest they should have approximately 350Ω/" * 40" = 14kΩ, but both measure 4kΩ. When stretched, they should increase by 350Ω/", but increase (very non-linearly) on average 75Ω/", depending on how quickly they are stretched. When relaxing the resistance initially increases on average 110Ω/", but after a few inches starts decreasing. It is difficult to read the resistance because as soon as the stretching stops, the resistance decreases rapidly.

Since the resistance increases on both stretching and relaxing a few inches, and otherwise gradually decreases, very little useful data can be obtained.

Is this typical of these sensors, or are the ones I received defective?

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adafruit_support_rick
 
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Re: Rubber Cord Stretch Sensor not as specified

Post by adafruit_support_rick »

I haven't played with that stuff, so I don't know. I'll check with somebody else...

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adafruit_support_bill
 
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Re: Rubber Cord Stretch Sensor not as specified

Post by adafruit_support_bill »

These are definitely not precision sensors. The material is not specifically designed for sensing purposes, so the conductive properties are subject to changer from batch to batch.

The piece I have here measured about 13.6K for 40". Stretching it a bit, it went up to around 20K, but relaxing it goes up to about 26K, before gradually declining to near the original value.

So your samples appear to have a substantially lower initial resistance than earlier batches. I'll check to see if current stocks are similar.

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adafruit2
 
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Re: Rubber Cord Stretch Sensor not as specified

Post by adafruit2 »

yah these are not actually 'sensors' - they are conductive cords that we are (ab)using as sensors :) the resistance may vary from batch to batch because they're only made for ESD uses, not for sensing. if you totally can't use them you can return them for a refund but if we replace them they'll just be different resistances.
i recommend taking base-measurements for each cord and using that as calibration.

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