Burkert Type 1110 - Handbuch (Seite 23)

1110 - 21
DIGITAL INDUSTRIAL CONTROLLER
english
A ratio control is a special type of follow-up control and/or external set-point input.
The task of a ratio control is to cause a controlled variable (PV1) to track another
process variable (PV2) within a specific ratio.
PV1 is described as the dependent variable, and PV2 as the command variable.
In the regulated condition of the ratio control, the following equation applies:
SPr = PV1 / PV2
SPr: ratio set-point
PV1: dependent variable (controlled variable)
PV2: command variable
This gives the internal set-point for the channel X1 that is to be controlled:
PV1set = PV2*SPr
SP = X2*SPr
5.5 Controller with additional functions for ratio control
5.5.1 Ratio control
Figure 11: Ratio control
Example:
Let us take mixture control of an acid/alkali flow as an example of a ratio control
system. The internal setpoint SP for the supply of acid (PV1 set) is generated by
multiplying the flow rate of the alkali (command variable PV2) with the ratio setpoint
SPr.
Multiplier
Controller
PID Controller
Setpoint
SP
Ratio
setpoint
SPr
PV1
Regulated
variable CO
Command
variable
PV2
Reference
system
Controlled system
Follow-up
system