Update of K-Tron Loss-in-weight Feeding Technology 12th Continuous Mixer and Extruder Users Conference Indian Head Division Presented By: Jim Rutter & Ron Letizia K-Tron America
Overview • Review of Loss-in-weight Feeders • Choosing the Proper Feeder • Advances in Loss in Weight Feeders for • Enhanced Performance • Getting Valuable Data From Your Feeders
Loss-in-weight Principle Feeder and material are continually weighed, and metering speed is controlled to maintain desired discharge rate.
f1 f2 f3 f4 7 8 9 RUN 4 5 6 STOP 1 2 3 ? 0 C ENT Theory of Operation of a Loss-in-weight Feeder WEIGHT SPEED (RPM) SETPOINT
Choosing the Proper Feeder For Your Application
Material - Physical Properties- Handling Characteristics- Rate Feeder - Operating Principle- Weighing System- Control System - Mechanical System Environment - Vibration- Temperature ACCURACY - User Specified- Required Quality- Minimum Cost
Determine the Process Performance Requirements • Repeatability • Linearity
Linearity Linearity is a measure of flow rate error over the full operating range
Repeatability Repeatability describes flow rate variability at a given rate setting
Other Considerations • Feedrate • Material Properties • Refill Method • Environment • Control Integration
Performance Timescales ACCURACY Momentary - Selection/Sizing- Weighing Resolution- Control Response - Environment Steady State - Measurement Stability - Maintenance Refill Phase - Refill Performance- Refill Frequency
Advances in Loss-in-Weight Technology to Meet High Performance Demands
Improved Load Cell Technology • Higher Sampling Rates (112 samples/sec) • Vibration - Digital Filtering • Temperature Compensation
Vibration Filtering vs. Non-Vibration Filtering
SFT Load Cells SFT II200 - 1000 kg SFT II18 – 120 kg SFT III60 – 1000 N
Screw Speed Modulation • Improved Short Term Accuracy • 2 Sigma at 10 Seconds Improved • Tremendously • Steady Material Output • Ideal for Low Feed Rates
Initial Situation In general, an attempt at aggressive control will fail and increase the mass flow variations. Additionally, during volumetric phases, such as refill or pert, the speed remains constant.
With Screw Speed Modulation The periodic pulsation of material is measured and screw speed is adjusted. The Speed Modulation Algorithm learns when and how much the mass flow changes periodically, and then changes the screw speed just before there will be an error. It continues modulation during volumetric phases such as refill or pert.
Connectivity Options • Options to Meet Any Plant Network Demands • Ethernet Compatibility • Wireless Capability
Getting Valuable Data From Your Feeder • The Communications Link • Collecting Data
Communication Link:Data Concentrators Host Computer or PLC High Speed Network Display/Data Concentrator Local Display
Communication Link:Gateways Host Computer or PLC High Speed Network GATEWAY GATEWAY GATEWAY Local Display
Communication Link:Direct Connection To Feeder TREND • No Bottlenecks • Less Components Host Computer or PLC High Speed Network Local Display
Direct Connection To Your Feeder What’s Important? CONTROLLER • Ease of Setup • Reliability • High Speed/Data Throughput • Deterministic • Supports large data transfers
What Protocol To Use? • Modbus RTU / ModbusPlus • AB DF1, Siemens 3964R • Profibus DP • DeviceNet / ControlNet • Ethernet-Modbus / TCP • Ethernet-Ethernet / IP CONTROLLER
Ethernet For Control TREND • High Speed • Proliferation of Products • Open Fieldbus Standards • Modbus/TCP (Modbus over Ethernet) • Ethernet/IP (DeviceNet over Ethernet) • Reliability? • “Deterministic” Question?
Ethernet “Determinism” • Ethernet does not provide consistent latency due to arbitration • algorithm called Carrier Sense Multiple Access with Collision • Detection (CSMA/CD). Delays Due To CSMA/CD Two Node Packet Collision BandWidth = 100 Mbits/sec, 1000 packets/sec 128 byte packet: 99% sure will run 1140 years without > 1 msec delay 1024 byte packet: 99% sure will run 2 years without > 1 msec delay (Source: “Can Ethernet Be Real Time”, Real-Time Innovations, Sunnyvale, CA)
Ethernet “Determinism” • Switches vs. Hubs • Switches virtually eliminate all collisions • by buffering packets • Max delay can be calculated • Slower on lightly loaded networks due • to imposed delays.
Collecting Data • Who uses the data? • (Operations, Maintenance Personnel, Quality Control) • Can the communications link eliminate I/O? • Can the data help determine end product quality and help with end product validation? • What control functions are required?
Collecting Data Advanced feeders provide a wealth of information • Real-time access to all process data and parameters • Access to diagnostic and service related information • Provides data and control functions for other feeder related components (such as pre-feeders and loaders) • Quick start built-in configurations to reduce learning-curve • Flexibility in configuration
Customizing Data Collection PC based tools help determine what parameters and data types will be exchanged.
Using Feeder Data Process data can be used to predict end-product quality problems or equipment failures before they occur. • Periodic catch samples validate feeder operation. Periodic end-product analysis validates the product. • Proactive approach may include collecting data in real time and statistically comparing it to “known-good” data to determine if run is likely to produce good end-product.
Conclusions • Trends toward direct feeder communications with high speed protocols • Industrial Ethernet gaining acceptance • Important to have access to all data with easy customization • Advantages to integrating feeder related equipment • Real-time data can be useful to predict problems and ensure end product quality
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