Evaluation electronics

The evaluation electronics forms the interface between the sensor and the control level. It acquires the raw electrical signals of a transducer, such as voltages, currents, pulses, or frequencies. These signals are amplified, filtered, and digitized. They are then evaluated mathematically, scaled, and converted into physical quantities such as mass, flow rate, pressure, or temperature. The evaluation electronics typically provides the measured values via standard signals (for example 4–20 mA, 0–10 V), fieldbus interfaces, or digital protocols of the control system. Additional functions such as limit value monitoring, dosing or control algorithms, averaging, or diagnostic functions are often integrated. In weighing and dosing systems, the evaluation electronics is decisive for measurement resolution, reproducibility, and response time—and thus for the accuracy of gravimetric processes.

The evaluation electronics forms the interface between the sensor and the control level. It acquires the raw electrical signals of the transducer, amplifies, filters, and digitizes them, and converts them by means of linear characteristics, for example

y = a · x + b

into physical quantities. Dynamic effects are often taken into account by simple filter models such as PT1 elements 

T · dy/dt + y = K · u

or by integrated PI/PID controller algorithms, such as 

u(t) = Kp · e(t) + Ki · ∫ e(t) dt + Kd · de(t)/dt

In this way, the evaluation electronics provides standardized output signals and supports dosing, weighing, and control tasks with high accuracy and reproducibility.

• y is the output variable (e.g., mass, flow rate, pressure, or temperature) in physical units.
• x is the input variable (e.g., voltage, current, or a digital raw signal of the sensor).
• a is the gain factor or the slope of the characteristic; it describes the scaling from the input signal to the physical quantity.
• b is the offset or zero point; it corrects a zero shift and shifts the characteristic up or down.
• u is the input variable (e.g., sensor signal or reference variable).
• y is the output variable after the filter or transfer element (smoothed or delayed signal).
• T is the time constant of the PT1 element; it describes how quickly the system responds to changes at the input.
• K is the static gain of the PT1 element (gain factor between input and output in the steady state).
• dy/dt is the time derivative of the output variable y and describes how quickly y changes over time.
• u(t) is the controller output (e.g., valve setpoint, speed setpoint, delivery rate).
• e(t) is the control error, i.e., the difference between setpoint and actual value.
• Kp is the proportional coefficient; it determines how strongly the controller reacts directly to the instantaneous deviation e(t).
• Ki is the integral coefficient; it weights the time-integrated error and ensures the elimination of steady-state control deviations.
• Kd is the derivative coefficient; it reacts to the rate of change of the error and damps rapid changes or oscillations.
• ∫ e(t) dt is the integral of the control error over time and represents the accumulated error.
• de(t)/dt is the time derivative of the control error and describes how quickly the error changes.