Ohjausarvo

Ohjausarvo, in Finnish control engineering and automation, denotes the desired or reference value of the variable being controlled. It serves as the target that the control system strives to attain and maintain, and it is often referred to as the setpoint or reference input in English-language literature.

In a feedback loop, the system continuously compares the ohjausarvo with the actual measured value (mittausarvo). The difference, or error, e(t) = ohjausarvo(t) − mittausarvo(t), guides the controller in selecting the appropriate manipulated variable (ohjausmuuttuja) to reduce the error. The goal is to drive the measured value toward the ohjausarvo despite disturbances or changing conditions.

Ohjausarvo can be static or time-varying. A constant ohjausarvo maintains a fixed target, while a time-dependent ohjausarvo follows a schedule or trajectory, such as a step change, ramp, or sinusoidal reference. This is common in process control, robotics, HVAC systems, and automotive or aerospace applications.

Implementation considerations include how the ohjausarvo is generated (manually set, scheduled, or derived from higher-level commands), how it interacts with safety limits and bumpless transfer during setpoint changes, and how it is communicated within the control architecture. In practice, it is often part of a control strategy that also includes measurements, disturbances, and constraints.

Related concepts include setpoint, reference value, and target trajectory. The term emphasizes the goal of the control system and distinguishes the desired state from measured performance.