Rub Block vs. Touchswitch
Choosing the right belt alignment sensor
Belt misalignment is a common problem in belt conveyors and bucket elevators. When the belt is severely misaligned it can cause damage to the machine casing while generating dangerous heat in dust hazard environments.
Two typical methods of detecting belt misalignment are the rub block and the Touchswitch.
The Rub Block consists of soft brass with an embedded temperature sensor. The sensor alarms when the brass heats to the trip temperature. Three main drawbacks exist for this sensor. First, by the time the brass heats, the belt has already been misaligning for a period of time. Second, the belt could periodically rub against the brass and move away, wearing through the rub block without ever giving an alarm, leaving you unprotected. Finally, there is no simple way to test the rub block without introducing heat into a potentially hazardous environment.
The Touchswitch design addresses these 3 issues. First, it detects the lateral force of the belt, and gives you an immediate voltage free relay contact change when the belt contacts it. Second, the face of the sensor is made of hardened stainless steel, which is much more resistant to wear than soft brass. Finally, each Touchswitch has a test knob and status LED, so you can tighten the test knob to simulate a belt misalignment and watch the LED go out followed by machine alarm/shutdown. When you loosen the test knob it simulates the belt moving off of the Touchswitch and the LED turns back on.
