S256 Force Sensor Application Notes
General Description:
The S256 Force Sensor is a monolithic aluminum bodied structure with a proprietary thin film technology strain gauge applied, capable of producing an analog voltage output in response to loading of up to 10, 30, and 80 grams depending on the model chosen. (Refer to Products Specification drawing SMD3277)
Physical Considerations:
Mounting: Two 0.126” diameter mounting holes are provided through the mid-section of the sensor body. Washer or spacers should be used between the sensor and the rigid mounting surface to preclude any interface with the sensor’s moving element.
Loading: Load forces may be applied in either direction to the free end of the sensor, perpendicular to its longitudinal axis and on center line of its #4-40 threaded hole. Single point contact is best and often achieved by contacting a spherical element with a flat surface. The design of the S256 sensor provides for the inherent overload protection up to 1,000% of its full load value.
Wiring: Color coded lead wires are provided for electrical connections, however when extended, adequate forms of strain relieving should be provided in the assembly design.
Electrical Considerations:
As seen in the schematic drawing, 4 resistive elements are created by propriety thing film technology in a Wheatstone bridge configuration and adjoining areas of strain concentration. The application of a load to the sensor causes an electrical imbalance between the resistive elements and produces an output voltage (typically in millivolts) that is linear and proportionate to the load applied. Less than the maximum excitation voltage may be used, however the resulting output will be reduced proportionately.
Environmental Concerns:
While the thin film technology is itself immune to normal humidity levels, care must be taken to avoid condensing moisture and direct water exposure. The S256 is very stable over time and temperature.
Precautions:
Due to the nature of the thin film technology, care in handling should be observed and no damage be allowed to occur, especially in the area of the thin film strain gauges. During handling and assembly procedures, anti-static discharge practices should be observed.
Recommended Mounting for S256 Load Cell
Ideally, load interface should be via a single point of contact, such as the intersection of a sphere to a plate or a suspension string.
The central section of the load cell is mounted to mechanical ground. The Upper and lower “beams” move with applied load. When mounting the load cell,
take care not to interfere with the load cell’s movement.
i.e. Neither the mounting block nor the head of the mounting screws should cover the narrow slot between the center beam and the upper and lower beams.