The Ratio (RTO) function block is usually employed to drive the flow rate of a secondary flow stream to a setpoint that is a specified ratio of a primary flow stream. The block has two inputs: IN_1, which is the flow rate of the primary stream and IN, the flow rate of the secondary flow stream. The Ratio block's setpoint is the ratio (secondary flow rate)/(primary flow rate). This output is normally fed out to a PID flow controller for the secondary stream.
The Ratio function block supports signal filtering, mode control, output tracking, and alarm detection. This function block is normally used in a cascade configuration and supports normal block-to-block communication through the BKCAL channel.
The following diagram shows the internal components of the Ratio function block:
