Tension Sensor Selection for Web, Wire and Cable Equipment

Web, wire and cable machines rarely measure tension directly in a straight line. A sensing roll, pulley or guide converts tension into bearing or shaft force according to wrap angle and geometry. Changes in angle, friction or alignment can alter sensor force without a true process-tension change. Selection therefore requires the full material path, tension range and machine dynamics. The sensor, roll, bearings, structure, amplifier and controller must be designed as one measurement loop.

Define material and operating states

Record web or cable material, width, tension range, speed, acceleration, roll diameter, splice, break and threading conditions. State whether the signal controls unwind, rewind, dancer or quality. Include the minimum stable tension and peak during emergency stop.

Calculate force from geometry

Draw entry and exit angles at the sensing roll and calculate resultant bearing force for the full travel range. Include changes caused by roll buildup, dancer position or product path. A calibration factor based on one wrap angle is invalid if geometry changes during operation.

Choose sensing architecture

Compare pillow-block sensors, shaft-end transducers, cantilever rolls and inline tension cells by space, capacity, bearing arrangement and maintenance. Decide whether one or both roll supports are measured. One-sided measurement may be affected by widthwise load distribution or frame twist.

Control mechanics and alignment

Design a stiff roll and frame with aligned bearings and minimal parasitic friction. Prevent cable pull, guards or adjacent rolls from loading the sensor. Thermal bearing growth and overtightened housings can shift zero. Verify free rotation and baseline output before threading material.

Size for range and dynamics

Include roll weight, bearing preload, process resultant, acceleration and upset loads. Retain overload margin while producing enough signal at minimum tension. Check sensor and structure natural frequencies. The selected bandwidth should capture control changes without amplifying irrelevant machine vibration.

Design signal and control behavior

Match excitation, amplifier, bipolar range, sampling and filter to the controller. Define update time, sign, zero procedure and fault state. Avoid automatic zero while material tension is present. Verify that filtering and communication delay remain compatible with loop tuning and emergency response.

Calibrate with known tension

Apply a traceable force through the actual material path or a controlled rope and weight arrangement at representative angles. Test both directions or machine states if geometry varies. Check individual supports, summed tension, linearity and repeatability. Record angle, roll position and signal settings.

Maintain the measurement loop

Inspect bearings, roll buildup, alignment, fasteners, cable and zero trend. Recalibrate after roll, bearing, frame, sensor, material path or controller changes. Investigate recurring zero shift mechanically before applying software offsets. Preserve as-found evidence for control-quality analysis.

Engineering checklist

• Document tension, speed and transient states.
• Calculate resultant force from wrap angle.
• Select one- or two-sided sensing deliberately.
• Control bearing and frame forces.
• Match bandwidth to the control loop.
• Calibrate through the real material path.

Frequently asked questions

Why can tension change when the web force is constant?

Changing wrap angle or bearing friction changes the force seen by the sensor.

Can the machine zero during production?

Normally no; zeroing with tension present hides real load and may corrupt control.

Is a faster sensor always better?

No. Sensor, structure, sampling and control bandwidth must be coordinated.

Decision record

Record the selected architecture, operating cases, assumptions, accepted limits and responsible approver. Attach drawings, calculations, calibration evidence and unresolved deviations. Define which mechanical, process, electrical or software change requires reassessment. Include the expected inspection interval, spare strategy, fault response and location of recoverable configuration files. Assign an owner and closure date to every conditional acceptance. Review the record after representative service and compare actual faults, drift and maintenance findings with the original assumptions. A concise decision record protects the engineering basis when equipment, personnel or operating conditions change.

Related measurement solutions

Industrial load cells · Weighing indicators