Photoelectric Fiber-Optic Sensor Detects Broken Parking-Brake Cable During Manufacture


During manufacture of automotive parking-brake cable, multiple strands of steel wire are twisted together, forming a single cable. After twisting, cable passes to the next process in an unsupported, continuous length. Occasionally, the cable breaks, compromising safety and damaging equipment. Although the cable’s exact path is unpredictable, a multi-beam fiber-optic sensor detects its presence, interrupting the process if it breaks.

Customer Values

  • Rapid, reliable detection of a small, fast-moving target with an erratic path
  • Elimination of downtime arising from broken cables
  • Highly cost-effective solution to a potentially costly problem

Specific Product Advantages

  • System switching frequency of up to 4000 Hz
  • Exceptionally reliable detection across a 90mm x 20mm envelope
  • Diffuse detector with simple set-up and teach-in function

Customer Application

During production of automotive parking-brake cable in a Portuguese factory, strands of steel wire are twisted together, forming a single cable with a nominal diameter of 3mm (0.1in). The process operates continuously, and twisted cable passes between successive work-stations in an unbroken length. Between operations, the cable is largely unsupported, assuming the form of a suspended catenary.

Occasionally, a manufacturing defect causes the cable to break. In this event, safety is compromised and, unless processing is halted, machine breakdowns occur. A sensor system must detect the presence of the cable as it passes from one operation to the next, interrupting the process if it breaks.

 Because the cable is unsupported, its path is unpredictable and its exact position at any time, particularly in the vertical plane, is unknown. The sensor system must detect the presence of the cable reliably at any point within an envelope 90mm (3.5in) high and 20mm (0.75in) wide.

Customer Solution


A Contrinex photoelectric sensor system, comprising a DIN-rail-mounted fiber-optic amplifier coupled with a multi-beam diffuse sensing head, provides an optimal solution for this application. With maximum switching frequencies of up to 4000 Hz and sensing distances of up to 150mm (6in), multi-beam fiber-optic sensors are ideal for detecting fast-moving targets. The PBTP construction of the sensing head ensures excellent mechanical protection in the production environment.

The 28mm-wide sensing face of the multi-beam sensor detects targets across its entire width, providing a detection envelope that comfortably accommodates the customer’s 90mm x 20mm requirement. Initial set-up is accomplished by means of a manual teach-in function and integral signal-strength LCD, following which the system operates without manual intervention.

A 2m-long fiber cable allows remote mounting of the fiber-optic amplifier; connection to the customer’s control system is via an industry-standard PNP interface and an integral M8 cable connector, allowing easy removal and replacement when necessary.

 The system tolerates high ambient-light conditions and detection of a broken cable is both highly reliable and immediate. If the cable breaks, the system interrupts the process and sounds an alarm, alerting the operator. Downtime arising from broken cables has been eliminated since the system has been operational.