Seed Coating

It is common for seed to be treated with pesticide, fertilizer and other things that will aid in the growth of the plant and its harvest yield. Some treatments require the processing of raw ingredients from a granular material in specific proportions, which are then batched and attached to the seed downstream in the process. This processing of raw ingredients often requires a fully automated grinding system to prepare the ingredients for the seed coating.

In this seed coating application, there are two granular raw materials. Both are dosed into a fine grinding machine at specific rates and proportions. Included in the process control and automation system for this grinding system:

• Two (2) Bulk Bag Unloading Systems w/ Surge Bin and Loss-In-Weight Feeder.
• One (1) Flexible Screw Conveyor w/ Surge Hopper.
• One (1) Fine Grinder.
• One (1) Existing Filter Receiver.
• One (1) Existing Silo.
• One (1) HMI/PLC Control Panel.
• One (1) VFD/Starter Control Panel.

While it is typical that Sterling Systems & Controls, Inc. provides the mechanical equipment for systems applications, in this seed coating grinding system application we provided only the design and manufacture of the two control panels, the HMI/PLC Control Panel, and the VFD/Starter Control Panel. Sterling Systems & Controls is a UL-listed control panel manufacturer certified for the USA and Canada.

HMI/PLC Control Panel & System Operation

Sterling Systems & Controls, Inc. understands the seed coating process, not just simply control technology.  We worked with the supplier of the mechanical equipment, Prater Industries, to make sure the mechanical equipment would do the job required by the customer and we designed and manufactured the HMI/PLC Control Panel as required, customized to do the specific job that was needed. The main operator interface for this system is via an Allen-Bradley PanelView 10” industrial touchscreen HMI, and an Allen-Bradley PLC mounted in an enclosure running a custom-engineered Sterling Systems & Controls grinding system process control application. The HMI/PLC Control Panel and PanelView HMI provide all control and equipment status information necessary to run the automated process control system for this seed coating application.

Each piece of equipment has a virtual MOA (Manual-Off-Auto) switch in the HMI. Placing all switches in the M mode allows the system to be operated manually. All switches must be in the A for the grinding system to operate automatically. The operator will use the HMI to select one of five previously stored sets of parameters to run. Each set of stored parameters contains the following data points:

• Raw Material #1 Speed Set-point (%).
• Raw Material #1 Agitator Speed Set-point (%).
• Raw Material #2 Speed Set-point (%).
• Raw Material #2 Agitator Speed Set-point (%).
• Target Fine Grinder Load (amps).
• Fine Grinder High Amps (amps).
• Fine Grinder Low Amps (amps).
• Filter Receiver Discharge Airlock Speed Set-point (%).
• Filter Receiver Fan High Amps (amps).
• Filter Receiver Fan Low Amps (amps).
• Fine Grinder Speed (%).
• Fine Grinder Feeder Airlock Speed (%).

After placing all switches in the A position, the operator will press the START button on the panel. The START button will flash during startup. The system will verify that the level in the material silo is NOT indicating a high-level condition. If a high-level condition is present, the system will generate an alarm and will not start. Next, the silo blower will be started and confirmed running. While the silo blower is running, the system will monitor for silo blower low pressure. If the silo blower low-pressure sensor indicates a low pressure for longer than a programmable time, the system will display a Low-Pressure alert on the HMI screen.

The above partially illustrates the customized process control system implemented by Sterling Systems & Controls, Inc for this application. This includes monitoring and controlling all items listed above to produce the necessary finely ground and blended material for further use in producing finished and coated seed. The HMI/PLC panel also includes all the weight instruments for the loss-in-weight feeders within the system.