Figure 4-1 Function Block Configuration Of A Typical Ratio Control Loop - Honeywell VPR100 User Manual

UNITS = FPS
INPUT TYPE = LINEAR
DIRECT/INDIRECT/SQRT = SQRT
RANGE LOW = 0
RANGE HIGH = 40
CIRCUIT LOW = 1
CIRCUIT HIGH = 5
ELECTRICAL UNITS = VOLTS
∆
AIR P
AI2
SIGNAL
∆
FUEL P
AI3
SIGNAL
UNITS = FPS
INPUT TYPE = LINEAR
DIRECT/INDIRECT/SQRT = SQRT
RANGE LOW = 0
RANGE HIGH = 40
CIRCUIT LOW = 1
CIRCUIT HIGH = 5
ELECTRICAL UNITS = VOLTS

Figure 4-1 Function Block Configuration of a Typical Ratio Control Loop

When the ratio control loop in Figure 4-1 is brought ON LINE, its ON LINE display must be accessed to
allow the instrument's SP (Set Point Select) key to be operational. To make the working set point of the
ratio control loop equal the equation
(WILD VARIABLE X RATIO SETPOINT) + RATIO BIAS
you must select the TUNE LOOP menu item TOGGLE SETPOINT SOURCE so that an "SP2" is seen in
the loop's ON LINE display. Note that within the ratio control loop's programming menu (accessed under
PROGRAM CONTROL LOOPS), you will not find a SETPOINT #2 menu choice. The ratio control loop
function block operates with the formula
(WILD VARIABLE X RATIO SETPOINT) + RATIO BIAS
assuming all the functionality of the ratio loop's second set point. Switching the working set point of a live
ratio control loop from SP2 to SP1 will essentially suspend any ratio control and cause the loop to behave
like a standard PID controller. This standard PID loop will have a local set point equal to the value
programmed for SETPOINT #1. To control the process variable using a fixed set point that is independent
of the loop's WILD VARIABLE input, toggle the ratio control loop's working set point to SP1.
12/00
FEEDBACK
AI2 OV
PV
WILD × +
AI3 OV
VARIABLE
RATIO
SETPOINT
TYPE = RATIO
SETPOINT #1 = 500
WILD VARIABLE = AI3 OV
RATIO SETPOINT = 0.50
RATIO BIAS = 0.75
GAIN = 10
RESET = 1
RATE = 0
VPR & VRX – User Manual
Programming Function Blocks and Features
AO2 BC
LP2
SP2
RATIO
BIAS
Working set point of loop when use of WILD
VARIABLE is desired to establish proper control
of PV. If ratio control using WILD VARIABLE
must be temporarily suspended, loop's working
set point may be switched ON LINE to SETPOINT
#1 via "SP (Set Point Select)" key on instrument's
front bezel.
4 TO 20 mA
TO AIR FLOW
CONTROL
VALVE
LP2 OV
IN AO2
OUTPUT TYPE = CAT
IN LOW LIMIT = 0
IN HIGH LIMIT = 100
OUT LOW LIMIT = 4
OUT HIGH LIMIT = 20
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