Figure 3-20 Complete Function Block Diagram Of Figure 3-15 - Honeywell VPR100 User Manual

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 3-20.
TYPE J
THERMOCOUPLE

Figure 3-20 Complete Function Block Diagram Of Figure 3-15

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.
12/00
AI1 OV
AI1
PV
INPUT TYPE = J
RANGE LOW = 0
RANGE HIGH = 1000
TYPE = STANDARD
SP1 = 500
GAIN = 10
RESET = 1
RATE = 0
VPR & VRX – User Manual
Programming and Operating Concepts
AO1 BC
FB
LP1 OV
LP1
4 TO 20 mA
IN AO1
OUTPUT TYPE = CAT
IN LOW LIMIT = 0
IN HIGH LIMIT = 100
OUT LOW LIMIT = 4
OUT HIGH LIMIT = 20
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