Conveyor Control Circuits

Separate circuits should be used for distinguishing between overload or jam conditions, and production stops. The first type usually requires the assistance of a maintenance electrician or a mechanic. The trouble must be located and cleared, and then a r,eset pushbutton is operated to restore service. See Fig. 2.

Production stops are made with maintain-contact type pushbuttons so that the system will start immediately after the button is returned to the run position. Local indicating lights, with about 25-watt off-white lamps, can be located above and adjacent to pushbutton stations. They should be located so that they may be seen from a distance.

Circuit Checking.

It is desirable to be able to monitor circuits from a central point. One method is to use the back contacts on emergency run-stop pushbuttons and limit switches to operate signal lights. This does not guarantee, however, that the actual operating contacts are functioning. Also, a large number of signal lights w~th nameplates is required.

At least one wire from a junction of each pair of contacts in a circuit can be brought back to the central panel. A tap switch with the center terminal connected to a small signal lamp can be used to sample each contact. A name card identifies each point. To check the circuit, the tap switch is rotated until the light shows. Then the next contact in the series is the one which is open. Operating circuits are checked quickly. Jams on conveyor systems must usually be cleared by reversing the drives. Jams may be caused by parts falling off, damaged carriers, or malfunctioning of a component. Drives can be reversed by manually operated reversing switches with extra contacts to block out holding circuits. A motor should run in reverse only as long as a jog pushbutton is held in. Reversible motor starters may also be used, with proper precautions.