Scale-Tron, automation, sensors and weighing systems

BULK TERMINAL CONTROLS - control material flow and inventory

Bulk materials such as grain, flour, cement, flyash and fracking sand, used in the extraction of oil and natural gas, are either milled on-site or shipped to the bulk terminals in rail cars and stored in silos.  The materials are then loaded into trucks from the silos for local deliveries or bagged, blended or batched into other products.  The bulk material control system supervises inventory, selects the silos to be filled, runs the filling conveyors and monitors progress.  In truck delivery terminals, a truck scale under the silo discharge points is connected to the control system.  The operator monitors incoming trucks, directs them to one of the silos and fills them automatically to preset weights.  The Baker-Hughes terminal in Shafter, near Bakersfield CA is typical.  This terminal has 12 silos of 610 tons capacity with 3 truck scales for loadout, each handling 4 silos.  Read about it in a World Cement Magazine Editorial.

Control system

The control system uses a PLC and touch screen as the operator interface;  no switches or lights are needed since everything is on-screen, eliminating mainenance issues and making it easy to upgrade.  The screen is located at the operator's desk while the PLC is located in the Motor Control Center, close by or in a nearby building where most of the motors are located, eliminating long runs of power cable and reducing the control wiring to a single ethernet cable.  When actuators are located in groups at long distances from each other, remote I/O can be positioned around the plant to further reduce wiring and cost.

Variable Frequency Drives are used to control the speeds of the rail car loadout conveyor and the bucket elevator.  Speed and other parameters are all all stored in the PLC and are accessible for update from the operator's screen with the appropriate passwords.

Variable Frequency Drives are used to control the speeds of the rail car loadout conveyor and the bucket elevator.  Speed and other parameters are all stored in the PLC and are accessible for update from the operator's screen with the appropriate passwords.  Other screens display data from the VFDs such as speed and motor current, useful for fault diagnosis.

Loadout and inventory control

A PC computer runs a special version of the BatchLink software which shows the on-hand inventory in each silo.  The BatchTron loadout control system loads trucks by automatically opening and closing feed gates to dispense material into each compartment as required, the weight values coming from the truck scales.  When complete the operator prints the delivery ticket and both the customer and inventory records are updated.

Since rail deliveries may not have the convenience of a local rail scale, deliveries are taken at face value but checked with the SiloWeigh.Net system below.  On-hand inventory values can be updated when errors need to be corrected. An Internet connection is used for service and training as necessary.

Camera system

A multiple camera system monitors incoming and outgoing vehicles plus the rail car discharge and bucket elevator discharge to the various silos, as well as allowing operators to guide trucks under the filling socks in the silos by mobile radio.  The latest cameras transmit data digitally via ethernet cable and ethernet switches at junction points throughout the plant.  The large screen display can be zoomed in on any camera for detail views.  A separate PC computer handles this operation, with a separate link via the Internet for service and updates.

This view shows the control console on left, inventory and SiloWeigh.Net computer on its right, camera display at top and scale indicators and ticket printers at lower right.

Silo inventory

Silo inventory is calculated from deliveries minus the truck loading amounts.  The SiloWeigh.Net system can be installed on all silos to further monitor actual silo loading as a cross-check on the calculated values.  6 to 8 sensors on the walls of 25 ft diameter skirted silos give stable readings of the weight within 2% of full scale.  The local PC computer allows the operator to view two screens;  one shows the levels in the silos or a history trend graph, as at right, while the other shows the inventory and truck shipments, plus the weight values from the truck scales.