Melfi Feed© Gravimetric Feeder Controllers
Are you having difficulties with your "black-box" feeder controllers? 
 

Melfi Feed© is the next generation of PLC-based Weighbelt, Loss-in-Weight and Flowmeter automated feeder controllers. The system is designed to directly replace the proprietary microprocessor equipment supplied by any of the popular LIW feeder manufacturers.

The Melfi Feed© PLC controller has been developed around the Allen-Bradley ControlLogix and CompactLogix hardware platforms, using standard RSLogix5000 programming software with Rockwell Automation RSView32 HMI. The field communications to the Hardy Instruments loadcell amplifiers are open standard Ethernet/IP components. We have created a cost effective solution using non-proprietary hardware to simplify the gravimetric feed control process.

Controller Features

∙ Weighbelt/Loss-In-Weight Feeder Selection
∙ Gravimetric Closed Loop PID Control
∙ Adjustable Digital Signal Filtering
∙ Adjustable Processing Sampling
∙ Select Alarm Enable/Disable/Shutdown
∙ Automatic Weighbelt Scale Taring
∙ Hardy WAVERSAVER® Vibration Detection
∙ RSView32 Human Machine Interface (HMI)
∙ Standard Components, Available Locally
∙ Field Expandable for Unlimited Feeders
∙ Programming IEC 1131-3 Compliant
∙ Remote Support via Modem or VPN
∙ Interoperability: control, process monitoring,
  communications, information collection,
  client/server based recipe and reporting all
  within one completely integrated and scalable
  feeding solution.

Retrofit Case History

Melfi Technologies has completed a gravimetric feeder control retrofit at a major polyethylene resins producer. Each of the two compounding lines consists of a single main powder resin LIW screw feeder running at 30,000 pounds/hour, with four powder additive LIW feeders running at 10-150 pounds/hour. 

The existing feeders were the conventional LIW-screw and weighbelt using vibrating wire loadcells. Maintenance for the proprietary electronics was becoming increasingly difficult, as parts and service were only available from the feeder manufacturer. The feeder manufacturer was pushing the customer to retrofit to their newest proprietary controller.

The maintenance manager began searching for a replacement control system that specified components available from local distributors. 

Downstream of the pelletizer there is weighbelt feeder to totalize the finished pellet stream. The belt feed rate is controlled by an analog level indicator in the prefeed hopper. The operator enters a level setpoint, and the PLC will control the belt speed to maintain the hopper volume.

Hardy Instruments C2® DeviceNet weighing modules were mounted onto the individual feeders to directly read the loadcell weight. The WAVERSAVER® signal filtering technology effectively eliminated any external influence from plant vibration.

Hardy Instruments C2® certified loadcells communicated the calibration parameters to the DeviceNet weighing modules, so the feeders could be calibrated without the need for calibration weights. Keeping all the field equipment on a DeviceNet network ensured only a single new field cable needed to be pulled for the entire loadcell retrofit.

The operator interface consists of a Rockwell Automation RSView32 local touchscreen monitor located in the control room, with a remote redundant touchscreen monitor located in the extruder panel for easy field access.

All external selector switches and indicator lights previously mounted on the panel door were relocated to the touchscreen to allow operation from either monitor.

Both lines were retrofitted, commissioned and operational within a two-week time span. The feeders continue to perform well, with greatly reduced downtime due to electronics failures. Since the initial commissioning there have been no additional service or repair return visits by a Melfi Technologies field engineer.