What is PV (Process Value)?
PV stands for Process Value — the measured actual value of a process variable within a control loop. Think of temperature, pressure, level or flow that is measured by a Sensor and fed back to a PLC or PID Controller.
PV = what the process is actually doing right now.
The PV is compared with the SP (Setpoint) to determine whether and how it needs adjusting.
🔁 Where do you encounter PV?
| Application | PV = measured value of… | Example sensor |
|---|---|---|
| Temperature control | Current temperature in a tank | Pt100, thermocouple |
| Pressure control | Air pressure in a pipe | Pressure transmitter |
| Flow control | Flow rate of water or gas | Flow meter |
| Level control | Liquid level in a vessel | Ultrasonic or radar level meter |
| pH control | Acidity in a reactor | pH probe |
🧠 How does PV work in a control loop?
- A sensor measures the current process value (PV)
- The PID controller compares PV with the desired Setpoint (SP)
- The deviation (error = SP - PV) is used to calculate an output signal (MV)
- The actuator (e.g. valve, pump or motor) reacts to bring the PV closer to the SP
📊 Example: temperature control in a mixing tank
- SP = 65°C (target temperature)
- PV = 62.3°C (current temperature measured by the sensor)
- MV = 57% valve opening for steam injection
→ The PID increases the valve opening to bring the PV up to the SP
🔗 PV in industrial systems
| System | Role of PV |
|---|---|
| PLC | Receives the PV via an analogue or digital input and uses it in logic |
| SCADA | Displays the PV in real time on HMI screens |
| Historian | Stores PV values for trending, reporting and analysis |
| DCS | Manages and optimises hundreds of PVs across a process plant |
📌 In summary
The Process Value (PV) is the heart of every control loop: it is what you measure, monitor and try to manage. Without a reliable PV, there is no effective process control.