Technical Support & Applications Engineering

Each Vibratory motor should have a separate overload to provide individual protection for over-current; these should be fitted with an accelerated trip in the event of a phase failure and the overload characteristic should be temperature compensated over the range of -5 degrees to +60 degrees C.

THE OVERLOADS SHOULD BE SET TO THE F.L.C STATED ON THE MOTOR NAME PLATES, UNDER NO CIRCUMSTANCES SHOULD THESE BE SET ABOVE THIS LEVEL.

When the power to the motor(s) is dropped, the motors slow down gradually, causing excessive vibration which can be detrimental to the equipment, supporting steel and dust seals.  To reduce this reverse phase braking should be used. Reverse phase braking operates by reversing two phases on both motors throwing the motors in reverse. When the stop button is pressed the phases are reversed to the motors for a period of time, this is controlled by a timer (T1 on the wiring diagram.)  When correctly adjusted, the timer will cut the power to the motors, just before their actual direction of rotation is reversed, hence the machine will be brought to a controlled stop with little or no bouncing.

THE EMERGENCY STOP FUNCTION OF THE PANEL WILL CUT THE POWER TO THE PANEL IMMEDIATELY; HENCE THE REVERSE PHASE BRAKING WILL NOT OPERATE.

Whilst the overload relays will provide protection for over-current, it does not prevent the operation of the equipment should a motor suffer complete loss of voltage, due to incorrect installation, severed cable etc

This is particularly important when the starter is used in conjunction with twin vibrators, where the loss of the supply voltage to one vibrator will result in the generation of a resultant centrifugal force in a circular mode, rather than the linear mode generated by two contra rotating vibrators.

This circular mode may cause excessive movement of the equipment in a horizontal direction with resultant mechanical damage.

We would therefore recommend the use of current monitoring relays, to monitor for loss of current so that:-

a) If one Vibrator only is connected in circuit when the “Start” button is pressed the “Start” button will be released. 

b) If during the normal running of both vibrators the supply cable to one vibrator is accidentally disconnected or severed, the power to both vibrators is immediately disconnected. 

Each vibrator is fitted with three PTC thermistors (one for each phase rated at 120oC or 160oC depending on the application.)  These are connected in series so that only two terminals exist in the vibrator terminal box and should be connected in series to a thermistor monitoring relay within the control to stop the machine in the event of a thermistor failure i.e. should the temperature of a vibrator exceed 120 / 160 deg C.