Honeywell VRX180 user manual Interconnections Between Function Blocks

Programming and Operating Concepts

TYPE J

THERMOCOUPLE

AI1 OV

AI1

INPUT TYPE = J RANGE LOW = 0 RANGE HIGH = 1000

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 3-14 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.

TYPE J

THERMOCOUPLE

AI1 OV

AI1

INPUT TYPE = J

RANGE LOW = 0

RANGE HIGH = 1000

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 3-15 Interconnections Between Function Blocks

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