Use the PID output as a normalized pump-speed demand, then scale and limit it before writing the PLC analog output. Do not tune the PID merely to force its output into the 0–10 V range; keep control and output conversion as separate functions.
Define the pressure-control direction
The process variable is inlet pressure from a 0–10 V, 0–1 bar sensor. The target behavior is unidirectional: keep the pump stopped at or below the 0.05 bar setpoint, then increase pump speed as pressure rises above it. Because higher pump speed assists discharge and is intended to reduce inlet pressure, configure the control direction—or the error sign—so a pressure increase above setpoint produces a positive speed demand.
The available evidence does not identify how the Elsist PID block selects control direction. Verify the sign during commissioning: raise the simulated pressure above 0.05 bar and confirm that OUT increases rather than becomes negative.
Scale PID OUT to the 0–10 V command
The documented OUT range is ±100%, while the analog command accepts 0–10 for 0–10 V. Since this pump command is unidirectional, clamp negative PID demand to zero and scale the positive range linearly. Process nonlinearity does not invalidate this conversion: the conversion only maps normalized controller demand to voltage, while KP, IT, and DT determine how the controller reacts to process behavior.
| Signal | Range | Conversion |
|---|---|---|
| Pressure sensor | 0–10 V = 0–1 bar | Pressure in bar = sensor voltage / 10 |
| PID demand used by pump | 0–100% | Negative OUT is limited to 0% |
| Analog command | 0–10 V | Command = limited OUT / 10 |
By direct calculation, 0.05 bar corresponds to 0.5 V from the pressure sensor, and 0.1 bar corresponds to 1 V. These are input-signal conversions, not pump-command voltages.
Configure and commission the PID
ST is the PID execution interval in milliseconds. IT and DT are expressed in seconds, while KP is dimensionless. Execute the PID at the same interval represented by ST; otherwise its integral and derivative calculations will not correspond to the actual update timing. The evidence supplies no tested KP, IT, DT, or ST values, so exact tuning values cannot be specified.
- Scale the pressure input into bar and use 0.05 bar as the pressure setpoint.
- Test the controller direction with simulated pressure and confirm that OUT rises when pressure exceeds the setpoint.
- Limit the usable demand to 0–100%, divide it by 10, and write the resulting 0–10 value to the analog output.
- Enforce zero pump command at or below the setpoint. Determine from the PID block documentation whether its integral state must be held or reset while stopped; the available evidence does not identify that interface.
- Commission the loop on the real hydraulic system and adjust KP, IT, and, only if required, DT while observing pressure oscillation and recovery.
FAQ
How do I convert a PID output from percent to 0–10 V?
Limit OUT to 0–100% for the unidirectional pump, then calculate the analog command as OUT / 10. Thus 0% commands 0 V and 100% commands 10 V.
What sensor voltage represents a 0.05 bar setpoint?
For a 0–10 V sensor scaled to 0–1 bar, 0.05 bar corresponds to 0.5 V. Scale the input into bar before comparing it with the setpoint.
Should the PID parameters be adjusted to produce only 0–10?
No. Tune KP, IT, and DT for the pressure response, retain OUT as a percentage demand, and perform the 0–100% to 0–10 V conversion separately.