The SG12 non-rotating torque/force sensor provides a fast easy-to use interface to any ¼, half, or full strain gauge bridge. It includes a lot of the optimizations in the SG3Q technology and offers both a digital serial and an analog interface.
With a 1ms sample rate and adjustable filters, the sensor module is useful for many non-rotating applications.
Torque/force-sensing based on strain gauges is a very well-known and well-understood technology. This is easy to apply to any shape and type of metal.
Features
- Fast and easy strain gauge interface
- Low power consumption (8.5mA)
- 1kSa/s sample rate, 1ms sample period, 500Hz Nyquist
- Serial data interface 230400 baud (N81)
- Analog output (12 bit resolution)
- Selectable digital filters
- Settable gain (x171/x285)
- Temperature sensor (±3C)
- LED indicator for activity/error
- Built-in data emulator for easy testing
- Compatible with Sensitivus SerialPlot Windows software (open source)
Technology Description
The SG12 module combines the superior zero-point stability, resolution, and accuracy of a strain gauge based solution with low power consumption in a compact design that can be directly integrated into many systems. For deeper integration, Sensitivus is available to help integrate the technology into another circuit.
For all non-rotating torque applications, this solution is simpler and more compact than the other solutions presented. Also, for systems where the rotation is limited and a cable to the partially rotating part is an option.
The sensor is using the same superior sensor technology and interface as the SG30 Sensor Kit and is thus also a viable way to do early testing of interface and basic technology evaluation.
Strain Gauges
Be careful to select the right type of strain gauge and bonding method. Consult the strain gauge manufacturer for instructions and recommendations.
Example data
Mounting area: 11.0×8.0mm (base size 8.5×6.3mm)
Enameled wires pre-soldered: 30mm length
Impedance: 2x1000R +/-0.1%
Gauge factor: 2.0 +/-1%
The number of strain gauges used in a given application depends on the actual requirements. Typically, half-bridge or full-bridge configurations are recommended.
Calibration
As with all torque/load cells, two distinct types of calibrations are normally performed.
Slope
Slope calibration is typically performed at the factory on each unit in a setup applying a known load. As the sensor is linear from positive to negative, only one other known point is needed. Typically, this is the zero point, as it is easy to establish.
Performing this calibration removes most effects of tolerances in strain gauge, bonding location, metal, components, etc.
This calibration value typically stays constant over the lifetime of the sensor.
Zero
Zero-calibration is the only other calibration needed. This needs to happen when zero torque is applied. Within a well-defined application, this may be possible to implement with an auto-zero algorithm. The SG12 module has a “zero command” to set the zero level (often called a tare function in a scale application).
Environmental Protection
To protect the strain gauge from humidity and light mechanical impact, a cover glue is recommended as a minimum. Consult the strain gauge supplier or bonding service provider for more information about this.
For best performance, the SG12 module and all exposed strain gauge connections should be covered with conformal coating as changes in humidity may influence measured values. The best way to do this is to “bake” the circuit at 60C for 20 minutes first to remove humidity.
