Position: The PLC-Based Belt Feeder Control was developed for Brabender Technologie’s Weigh Belt Feeders. Weighing software Code is available for Allen-Bradley ‘PLC-5’ and ‘SLC-500’ PLCs and some Modicon PLCs. Others may be available on request.
ADVANTAGES
* Uses non-proprietary PLC based hardware.
* Compact reusable software.
* Gravimetric closed loop PID control.
* All control parameters accessible via human machine interface (HMI).
* Adjustable belt load sample size.
* Automatic belt taring.
* Optional belt slipping/breakage detector.
* Supports a variety of pre-feeder mechanisms (optional).
* Ten user configured alarm conditions.
A quality weight controller is enable the feeder equipments work more safely and efficiently.
* One Feeder Module
The weigh belt feeder program file is written and configured to run one feeder. For multiple feeder configuration, this file has to be copied using indexed addresses.
* User Configured Alarms
Alarm detection is provided for start conditions, belt load, motor speed and feed rate deviations. In each case the user can easily modify the alarm limits and delay time. In addition, each alarm can be selected to cause a warning or shut down.
* Gravimetric Closed Loop PID Control
Based on belt loading and motor speed, the PLC calculates the actual feed rate and adjusts the motor speed to maintain the feed rate at set point. Control is manifested through a built-in PID control algorithm providing quick response to process upsets.
* Adjustable Sample Size
The size of the averaging belt load sample queue is adjustable and provides filtering to prevent over-controlling due to noise and normal process variations.
* Automatic Belt Tare
On command, the PLC runs the feeder empty (no pre-feed) for a pre-set time to determine the unloaded load cell signal or tare weight. The tare weight is subtracted from the belt load to obtain the net belt load.
* Optional Belt Slippage / Breakage Detector
A sensor mounted on the driven belt roller allows the PLC to determine if the belt is actually moving and alarm on failure.
* Compact Reusable Software
The core belt control algorithm has been written to support multiple belt feeders with no code duplication. This is accomplished by making extensive use of the PLC program and data file structure along with indirect addressing instructions. This greatly reduces memory requirements and code maintenance modification efforts.
* Control Parameters Accessible Via HMI
For further usability and friendliness, the user may interface to a human machine interface (HMI) compatible with the specified PLC.
SPECIFICATIONS FOR CONTROL OF BELT FEEDER(S) USING A PLC AND A HUMAN MACHINE INTERFACE (HMI)
1. Scope of Work
The scope of the specification is to provide the necessary information to an end user to properly select and configure a PLC and HMI system to accept the belt feeder control package.
2. Requirements I/O Requirement
The I/O requirements vary as per the number of feeders controlled and the selected feeder configuration: belt feeder with or without pre-feeder. As a minimum, each feeder requires the following:
-One analog input (AI) for the load cell. -One analog input (AI) for the belt weigh feeder speed feedback. -One analog output (AO) for the speed control. -One digital output (DO) for the motor controller enable.
Additional I/O (such as: manual/auto switch indication, pre-feeder control and indication and low level in hopper) can be added as necessary.
3. HMI Hardware Requirement
Any type of HMI is compatible with the specified PLC.
4. PLC Software Requirement
BTI will supply diskette with the PLC ladder logic. The BTI program is developed using RS-Logix for Allen-Bradley and ModSoft or ProWorkx for Modicon. The ladder logic is commented rung by rung. The end user shall also specify the number of feeders to be controlled, the I/O allocation and the type of feeders (with/without pre-feeder, with/without belt breakage sensor).
Program File Usage
As mentioned, the weigh belt feeder program file is written and configured to run one belt feeder. The I/O list is generated according to the specific application according to the I/O requirements. For Allen-Bradley PLCs, the file size is approximately 1.5 Kb. For Modicon PLCs, the file size is approximately 3.5 Kb. The program can be duplicated as many times as necessary up to the PLC memory capacity (considering also the I/O capacity, which usually is not a problem).
