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Programming and Operating Concepts
Video Recorder – User Manual 63
AI1
TYPE J
THERMOCOUPLE
AI1 OV
INPUT TYPE = J
RANGE LOW = 0
RANGE HIGH = 1000
LP1
PV
LP1 OV
TYPE = STANDARD
SP1 = 500
GAIN = 10
RESET = 1
RATE = 0
AO1IN
4 TO 20 mA
OUTPUT TYPE = CAT
IN LOW LIMIT = 0
IN HIGH LIMIT = 100
OUT LOW LIMIT = 4
OUT HIGH LIMIT = 20
Figure 3-14 Labels For Internal Function Block Parameters
Note that the internal parameters that we have specified in the function block diagram built up so far are
based largely on what can be inferred from the elements of the control configuration depicted in
Figure 3-11. These internal parameters will relate directly to settings found in instrument programming
menus that exist for each particular function block. As your experience and familiarity with programming
the instrument increases, you will become more familiar with some of the less intuitive parameters and
you will include these in your diagrams.
5. Connect the blocks
The next step is to connect the function blocks in the diagram. Refer to Figure 3-15.
The interconnection lines drawn depict the flow of information between function blocks and represent
how the blocks work together to support the complete control strategy. As shown, the furnace zone
temperature measurement that AI1 generates will essentially be used as the process variable of the LP1
control loop. Based on the values of the loop’s tuning constants and on how far AI1 OV deviates from
the 500 ºF set point, the control loop function block’s PID algorithm will accordingly adjust LP1 OV to
whatever value will be necessary to maintain the process’ set point. LP1 OV, which ranges from 0 to
100 %, will in turn be applied to AO1’s input to drive the 4 to 20 mA control signal applied to the valve
actuator. By modulating the valve actuator’s position, this 4 to 20 mA signal will regulate the gas flow to
the furnace zone burner and thereby allow the instrument to control the heat levels measured in the
zone.
AI1
TYPE J
THERMOCOUPLE
AI1 OV
INPUT TYPE = J
RANGE LOW = 0
RANGE HIGH = 1000
LP1
PV
LP1 OV
TYPE = STANDARD
SP1 = 500
GAIN = 10
RESET = 1
RATE = 0
AO1IN
4 TO 20 mA
OUTPUT TYPE = CAT
IN LOW LIMIT = 0
IN HIGH LIMIT = 100
OUT LOW LIMIT = 4
OUT HIGH LIMIT = 20
Figure 3-15 Interconnections Between Function Blocks