Stretch Sensors (Resistors)
A stretch sensor is a flexible, cylindrical cord designed to measure mechanical displacement through changes in electrical resistance. Often functioning as a wearable or embedded variable resistor, these sensors provide a simple yet effective way to translate physical motion into digital data.
As the sensor is elongated, its internal conductive path narrows and lengthens, leading to a predictable increase in resistance that can be measured by standard microcontrollers.
How Stretch Sensors Work: The Resistance Relationship
The core functionality of a stretch sensor is its ability to act as a variable resistor where the output is determined by the intensity of the stretch. This relationship is generally linear within specific ranges:
- Initial Resistance: The base resistance measured when the cord is at its relaxed, "nominal" length.
- Stretch Correlation: Typically, when the sensor is stretched by 50% of its original length, the electrical resistance doubles.
- Output Signal: By using a simple voltage divider circuit, this change in resistance is converted into a varying voltage signal that represents the degree of displacement.
Primary Applications for Stretch Sensors
Because of their flexibility and durability, these sensors are ideal for environments where rigid traditional sensors (like potentiometers) cannot be used. Key applications include:
- Biometric Displacement Reading: Monitoring human movement, such as chest expansion for breathing analysis or joint flexion in physical therapy.
- VR Suits and Gloves: Providing real-time haptic feedback and motion capture for virtual reality and gaming interfaces.
- Robotics & Air Muscles: Acting as a feedback sensor to determine the contraction state of pneumatic "air muscles" or flexible robotic limbs.
- Stress & Tension Measuring: Industrial physics experiments where measuring the tension on a cord or cable is required.
- Wearable Technology: Integration into smart clothing for posture monitoring or athletic performance tracking.
FAQ – Stretch Sensor Integration
1) Are stretch sensors waterproof?
Most stretch sensors are made of rubber or silicone-based materials, making the cord itself water-resistant. However, the electrical connections at the ends must be sealed or potted if used in moist environments.
2) Can I use these for precision weight measurement?
No. Stretch sensors measure displacement (change in length), not force or mass. For weight measurement, a load cell is the appropriate sensor.
3) What is the lifespan of a stretch sensor?
Lifespan depends on the "stretch cycle." Over-stretching beyond the manufacturer's recommended percentage can lead to permanent deformation and inaccurate resistance readings.
Need to Integrate Sensors into Your Building Network?
Chipkin specializes in taking data from specialized sensors and bridging it to BACnet, Modbus, or LonWorks. Whether you are measuring biometric data or industrial stress, we have the gateway solution for you:
