Honeywell VRX180 Draw the Feedback connection, Complete Function Block Diagram Of Figure

Programming and Operating Concepts

6. Draw the Feedback connection

To fully complete the function block diagram, one final and very important interconnection must be drawn. In setting up control loops in this instrument, a feedback path must be specified between the loop function block itself and the hardware element that externalizes the loop’s output to the real world. That is, the control loop block needs confirmation from the analog output block connected to it that the percent output levels it calls for have been correctly translated into accurate output signals. The feedback path that provides LP1 with this confirmation is established by means of program settings depicted in Figure 3-16.

TYPE J

THERMOCOUPLE

AI1 OV

AI1

INPUT TYPE = J

RANGE LOW = 0

RANGE HIGH = 1000

	AO1 BC
FB
PV	LP1 OV		4 TO 20 mA
LP1
		IN AO1
TYPE = STANDARD		OUTPUT TYPE = CAT
SP1 = 500		IN LOW LIMIT = 0
GAIN = 10		IN HIGH LIMIT = 100
RESET = 1		OUT LOW LIMIT = 4
RATE = 0		OUT HIGH LIMIT = 20

Figure 3-16 Complete Function Block Diagram Of Figure 3-11

Here, the function block diagram is drawn to include the key components of a typical loop feedback path. The AO1 function block has been changed to feature a second output denoted “AO1 BC.” This output has been connected to a feedback input at LP1 identified by the notation “FB.” The “AO1 BC” designator stands for “Analog Output 1’s Back Calculation.” When the control loop is brought on-line, AO1 BC will essentially represent the value of AO1’s 4 to 20 mA output at any particular instant. The term “Back Calculation” is used to reinforce the idea that this information is being sent “upstream” against the flow of all other information within the function block diagram.

64 Video Recorder – User Manual