Weighfeeder

VARIABLE SPEED WEIGH FEEDER OVERVIEW:

Block Schematic:

Weigh Feeders do a continuous weighing and controlling of bulk material feeding as per desired set point. Two single Point Load cells of required capacity are installed below Weighing Idler/rollers to get load applied on belt at particular area (i.e. silent Zone) by moving material, which in turn connected to Load transmitter to convert it into 4-20mA out put. In a second 30-40 weighments are done for bulk material running for desired accuracy. Optical encoder is fitted on driven roller which generates 1000 pulses per revolution of belt speed sensing roller. The Optical encoder converts slow speed of the conveyor belt in to high speed pulses to get desired accuracy.

The Micro controller based Weighfeeder controller receives the Weight in terms of Kg/mtr from Load transmitter and speed in terms of pulses/Min from optical encoder. It processes this two inputs received from the field and calculates the feed rate in the form of Tons per hour (i.e. TPH) also calculate the cumulative weight passed through the Weigh feeder.

Set point TPH and start command can be given from the 3 locations (i.e. Local Panel , WF Panel & Master PLC) based on the selection switch (i.e. mode of operation) provided on WF Panel, whereas stop command can be given from all the locations irrespective of mode of operation.

Firstly, operator needs to decide mode of operation by selection switch provided on WF Panel and give set point from selected location. On receiving the start command to WF controller, it start the motor, derives actual feed rate as explained above, compares it with set point and generates output for Variable frequency drive to correct the speed to achieve desired feed rate (i.e. set point) in few seconds. It also receives the material starvation signal from the field at least 10-15 min before actual material is getting over to generate alarms to enable to load the material in day bin.

The accuracy particularly depends on the calm tape operation and consistent material spread on carrying belt.

There is a provision to adjust the Load cell height and to remove the material deposits on the conveyer (on line) to get better accuracy.

Operation: (Note: Please refer attached diagram)

The panel is to be interfaced (inputs - Load transmitter, Encoder, material starvation, Emergency switch, Belt sway and Output – Variable Frequency Drive) to the weigh feeder frames /assembly of required capacity. Controller will derive the feed rate after processing the data from Load transmitter & Encoder.

Weigh feeders can be operated from three places (i.e. master PLC/DCS, Weighfeeder control Panel and Local Panel). On getting start command from master PLC/DCS, Weighfeeder control Panel and/or Local Panel, it shall control the feed rate by varying the belt speed as close to the set point TPH entered in to Weighfeeder panel or received from the master PLC and Local panel and give feedback (i.e. actual feed rate & Belt speed in form of 4-20 mA, cumulative weight for Totalization, feeder status like ON/OFF, feeder ready, etc in the form of Digital out puts) to master PLC and actual federate to local panel.

Remote Mode (WF Panel) operation:

The user can control weigh feeder remotely from the weigh feeder panel itself by using controls provided on controller. If remote mode is selected then only one can change the set points and give ON commands for WF from WF panel itself. Controller shall give required data to Master PLC and Local panel as explained above. WF shall stops on receiving the OFF command from Master PLC, WF panel or emergency stop switch operation from the field

Master Mode (PLC) operation:

For Master mode operation, the user sets the set points from the PLC and read into weigh feeder panel through AI in turn updates the set point in WF controller. (If required communication bus can be provided

WF controller controls the feed rate on getting the ON command from PLC and gives required data to Master PLC and Local panel as explained above. WF shall stops on receiving the OFF command from Master PLC, WF panel or emergency stop switch operation from the field.

Weigh feeder panel:

Main panel fabricated using extruded sections/CRCA sheets duly powder coated with

Siemens grey RAL 7032 shade.
Large size backlit STN LCD HMI for operation commands and displaying parameter values (Actual & Set point Alarms) and local operation.
Modular construction of controller for ease of maintenance.
Available for Capacity up to 100 T/Hr
Control and Electronics for accuracy +/- 0.5 % or better depending upon material characteristics provided.
Micro controller based systems ensures highest possible reliability.
User friendly, use of reputed make components/parts., Non proprietary parts
Feed mode and measuring mode selectable (Gravimetric and Volumetric)
Starvation monitor (buyer to provided the signal)
Encoder for speed sensing. Reference encoder for detecting belt slip (optional)
Micro controller based Controller for local operation with 2 Line display for cumulative Weight, feed rate set point, actual feed rate (optional at an extra cost)
Communication to higher supervisory system by Analog/ RS485/Ethernet etc.
Fully automatic zero and span calibration (outputs are provided for putting the weights)
Highly reliable 32 bit microprocessor based controller.
Simple calibration with standard weights.
Can be operated from any location viz: local panel, WF panel or Master PLC
Control ratio 10:1 provided.

Interfacing with VFD:

DI - VFD On/off

AO - Control Output

DO - VFD On

Interfacing with Master PLC:

DI - WF On/off

Belt sway

E stop

AI - TPH Actual

DO - WFD On

Local/Remote

Gravimetric/Volumetric

Interfacing with Master PLC/DCS:

Weighfeeder can communicate with master PLC/DCS by RS485 port, Ethernet port or Digital and Analog signals as per users requirement. This interfacing shall be discussed at later stage.

Weigh feeder mechanicals:

1. Main frame MOC is sectional steel structural channels with necessary stiffeners and supports, rigid heavy duty construction

2. Crowned Pulleys, Rubberized drive pulley provided to avoid belt slip.

3. Screw take-up unit for belt tensioning and centering.

4. Belt inside and outside scrapers provided for cleaning

5. Precision machined rollers used in weigh zone for achieving high accuracy.

6. Load cells in IP65 housing, precise temperature compensated load cell for drift-free operation and control.

7. Digital speed sensor mounted on non drive pulley shaft to sense the actual belt speed.

8. Life time lubricated idlers

9. Special belt for weighing task with continuously vulcanized joints provided.

10. AC 415 V, 3 phase motor for driving the belt. Motor and Gears reputed make will be provided.

11. Capacities up to 100 Tones / Hr.