USES OF ELECTRICAL& INSTRUMENT IN CONVEYING SYSTEM

 E & I ASPECTS BELT CONVEYORS

A Conveyor Belt consists of two or more pulleys, with a continuous loop of material that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the Drive Pulley while the unpowered pulley is called the Idler. 

ELECTRIC MOTOR ATTRIBUTES:

TYPE:  SCIM , WRIM or DC Shunt/Compound motors.

  Mainly SCIM is used.

ENCLOSURE: Open  Drip Proof Type (ODP) 

  (A)  It gives protection from falling water 

  (B)  Splash Protection

  (C)  Forced Ventilation design

SPEED: Normally 1800 rpm or 1200 rpm.

VOLTAGE: Common conveyor AC motor application voltages are 230, 460, 575, 950, 2300, 4160 & 6600V AC. DC Motor application voltages are 250, 500, 600, 700, 750V DC.

BEARINGS:

vConveyor rotating motors are available in Ball, Roller & Sleeve Bearings.

vCommonly bearings are deep groove ball bearings with grease lubrication.

vChoice & availability depends upon speed, size and local practices.

MOTOR PROTECTION

vWINDING TEMPERATURE: In conveyor environments heavy duty Pt100 RTD’s are most common choice for temperature measurement.

v

vBEARING TEMPERATURE: Pt100 RTD’s are best choice. By embedding a RTD sensor within bearing housing, the belt control system may monitor the bearing temperature.

v

vVIBRATION: Vibration control system generates alarm but does not shut down the motor on belt conveyors.

vBELT OVERLOAD PROTECTION

BELTPROTECTION CONTROLS

BELT ALIGNMENT :

vBelt alignment sensors are positioned along the edges of the conveyor fabric.

vThey are generally at discharge and at loading zones of conveyor but can be  distributed along the conveyor at intervals.

BELT OVERLOAD:

vThe belt conveyor system is protected from belt overload by the motor overload.

vThe motor over load can be bi-metallic strip type protection.

vThe overload protection can be by belt weigh scales also.

BIN LEVEL:

  When conveyor discharges into bins or hoppers, bin level sensor provides protection to belt conveyor.

SIDE TRAVEL SWITCH/ DRIFT SWITCH/BELT SWAY SWITCH

vUsed to detect if a belt conveyor has moved too far away from its’ center line in either direction.

vA fault is then displayed, or the equipment is shutdown in order to prevent damage to the Belt Conveyor structure.

v

PULL CHORD SWITCHvPull Cord switch also known as Rope Operated Emergency Switch is used as a safety switch to stop the belt conveyor belt in case of an emergency.

vPull Cord switches are housed in a dust and weatherproof enclosure.

v These switches have got an operating handle with  steel rings at both ends for fixing the rope.

vThe switch is designed with manual reset type of mechanism.

OPERATION:

  Pull Chord switch is mounted on the walkway side of the conveyor belt, preferably at About 20 Meters. When the rope is pulled from any side, the switch gets operated.  Unless and until the handle is reset manually to normal position, the switch remains in operated condition.

LOCATION OF PULL CHORD SWITCH

NOTE:

vFor walkway on one side of the belt the location of pull chord shall be on one side only.

vThe pull chord shall be located as per the above options either above the belt or below the nip points depending on the location of the walkway. Two pull chords are not required.

ZERO SPEED SWITCH(ZSS):Speed Switches are devices which are shaft or pulse driven and can indicate or control the rotary motion of the equipment they are attached to. Zero speed switches are widely used as interlocks on conveyor systems of all types. When driven from a critical shaft, a zero speed switch can be electronically connected to:

v Actuate a signal or alarm device

v Break a circuit to a motor

v Make a circuit to start aux. equipment

v Make or break  to other electrical devices

v Signal a control station PLC

ZSS IN VARIOUS CONVEYING SYSTEMS

SEQUENCE OF OPERATION OF CONVEYOR BELTS:

vConveyors are switched on in opposite direction of  transport.

vThe opposite sequence is followed while switching off.

BELT PROTECTION INTERLOCKING:v

Conveyor control strategy that shuts down all upstream conveyors in event of a fault.

vPrevents loading onto Static Conveyor.

OPERATION & APPLICATION OF LIMIT SWITCHES

The equipment pushes the switch roller/ lever  actuating the switch  contacts.  The  heavy  duty  actuating  mechanism  is  designed to absorb hits of heavy machinery without damaging the internal mechanism. Limit  switches  are  enclosed  in  heavy  duty  weatherproof  enclosure. 

  Heavy duty limit switch are extensively used on EOT Cranes,  Conveyors,  Transfer  Cars,  Elevators,  Steel  Mills  &  Mobile  Material  Handling  Equipments  for  sensing  of  end  limits  and position sensing.

OPERATION & APPLICATIONS OF PROXIMITY SENSORSv

Proximity Switches are mainly used in Belt Conveyor Protection.

vIt is used as an interlocking for the protection of personnel & machinery.

vSafe Guarding of machinery is provided with the Proximity Sensors. If guarding is opened then Belt Conveyor would stop automatically.