PRODUCT SPOTLIGHT: The TSA – Safety Under Tension

US Tower Corp’s Tension Sensor Assembly (TSA) is a specially engineered and patented safety device (US Patent 8,766,812 B2). The TSA warns against and/or prevents a potentially catastrophic safety event due to main lift-cable over-tension or under-tension. Any action or condition causing the tension in the main lift-cable to become higher than normal will actuate the TSA’s high tension sensor causing an audio alarm and visual indicator warning the operator of a potential hazard.  When the high-tension alarm is triggered, the tower’s extend function is disabled for safety to prevent further loading of the cable.  The retract function remains enabled to allow the operator to lower the tower thereby reducing the main lift cable load. If an action or condition causes the tension in the lift-cable to become lower than normal, a low tension sensor triggers an audio alarm and visual indicator warning the operator of a potential hazard.  When the low-tension alarm is triggered, the tower’s retract function is disabled to prevent the main lift cable from becoming slack.  The extend function remains enabled to allow the operator to raise the tower thereby increasing the main lift cable tension.

The system includes a mechanical assembly that attaches to the towers base section.  The main lift-cable is routed through the mechanical assembly.  Pivoting arms inside the assembly rotate in response to the lift cable tension.  The arms have sensor targets that trigger the sensors and in turn cause the alarms.


The high tension pulley frame has a center pivot point.  It also has a spring canister applying force to it at all times.  The force is greater than the force resulting from the main lift-cables influence during normal operation.  If the lift cable force becomes higher than normal, the arm will rotate.  At a set cable tension, the movement of the arm will trigger the high tension alarm.  When the alarm is triggered, the tower extend function is disabled preventing damage to the system.


The low tension arm is constantly under spring tension.  The tension is much lower than the cable tension required for normal operation of the tower so it stays at rest against a stop during normal operation. It only moves if the cable tension goes below the normal tension used to operate the tower.  If the cable goes slack for any reason, the low tension spring begins to relieve allowing the low tension arm to move.  As the arm moves, it pivots upward until eventually it triggers the low tension alarm disabling the tower retract function.

See the product page for the TSA here:

US Tower Tension Sensor Assembly