Controls
For many years we use systems with programmable logic controllers (PLC systems) in our weighing and dosing systems. Our systems work as local systems in the sensor / actuator level. Optionally, we can implement higher-level distributed systems independent of the installed local systems. All controllers can be equipped with long-term data archives to ensure that the manufacturing process can be identified at all times or to maintain historical series of measurements within the scope of quality assurance.
Differential Dosing
For a gravimetric “loss-in” Weight “-Dosier device according to the differential balance method, the mass flow is determined as follows: The system weight is detected in each case after a measuring time .DELTA.t. The weight decrease ΔG after the measuring time Δt determines the dosage per unit time (mass flow = ΔG / Δt)
Consequences
The current measured value of the mass flow is available only at discrete times. The dosing controller must always wait for a measuring time Δt before a correction of the discharge can take place (“the control always runs after”).
Remedy
Use of an integral dosing unit according to the integral-balance procedure “Loss in Weight” Feeders:
Integral dosing units based on the gravimetric “loss-in-weight” method are suitable for exact dosing of liquids, pastes and bulk solids (powders, granules, fibers, etc.)
Important features
Great operating range with consistently high accuracy
Extremely high short-term accuracy
Functionality
The dosing hopper and the discharge unit are stored on a weighing system. A mechanically decoupled refill hopper cyclically fills the medium into the dosing hopper. The decrease of the system weight per unit time corresponds to the dosing capacity.
The dosing hopper is filled (at the start or after refilling). The setpoint calculator takes the weight reading. The setpoint calculator continuously calculates the decreasing weight setpoint from the decreasing system weight while the discharge is running. The dosing controller continuously compares the weight measured value with the calculated weight setpoint. The difference between the two values is processed continuously in a control circuit to correct the discharge. During a refill, the control signal average of the last 10 seconds will control the dispenser aggregate. The media properties will determine the appropriate dispenser aggregate (supplemented, if necessary, with additional dispensing aids). The media properties determine the appropriate output aggregate. The required dosing rate determines the device dimensions and the mechanical structure.
Batch Dosing
In batch batching, the specified weight of a batch (“batch”) is metered into a specified receiving container (mixer, filling, etc.). The weight setpoint can be set on the controller or taken over by external systems. As a rule, we use smaller touch panels in conjunction with Siemens S7 controllers. Our devices achieve very high accuracy so that additional weighing (for example from the mixer) can be dispensed with. Depending on the application, our devices can be optimized for the required cycle time. Our batch metering control can be programmed to dose the weight within a certain period of time, e.g. You want to dose 1 kg over one hour.
Continuous Dosing
For continuous dosing, the setpoint is specified in weight / time unit, the device runs continuously with this dosing output and receives in the rules a start / stop signal from a higher-level controller. Through automated refilling the dosage can be done in continuous operation “24/7”.
