Selecting a constant force spring for a displacement sensor
A displacement sensor may use a constant force spring to maintain a controlled pull as a measuring element travels. The selection begins with the movement and force needed by the sensor assembly, not with strip dimensions copied from another design.
Specify the required pull
State the target force and whether a range of force is acceptable over the working travel. “Constant force” describes the spring’s general operating behavior; it does not mean that every point of travel will have exactly the same force. If the sensor has a return mechanism or other moving parts, include their influence on the force requirement.
Define the travel and installation
Provide the minimum and maximum extension, normal working range, available space for the coil and the path followed by the strip. Identify the mounting orientation and the connection to the moving element. A spring that meets a force target can still be unsuitable if the strip rubs on another component, bends around an unintended edge or cannot be assembled in the available space.
Consider operating conditions
The extension speed, cycle target and environment affect the review. Material choice should reflect both the required performance and exposure to moisture or other conditions. A grade such as SUS301 may be considered for suitable projects, but corrosion performance and fatigue life must be checked against the actual design and test conditions.
Agree on validation before ordering production
Ask how pull force will be measured: at which extension points, at what speed and after how many cycles. Define the permitted force variation and the acceptance criteria for the assembled sensor. Confirm the strip end connection and the test method for any environmental requirement. These details allow the sample to be evaluated against the same conditions that matter in use.
Send the sensor layout or sample, target pull, usable travel, mounting dimensions, expected cycles and estimated annual quantity. If some requirements are still open, label them as provisional so the engineering team can identify the decisions needed for an initial design.
