Honeywell VPR100 User Manual page 113

Prompt
RATIO SETPOINT
SETPOINT SELECT OFF, discrete parameter, 0,
1
SETPOINT#1 & Setpoint #1 can be a
SETPOINT#2 number only. Setpoint #2
can be a number, an analog
parameter, or OFF.
12/00
Table 4-10 Loop Prompts (continued)
Range/Selections
VPR & VRX – User Manual
Programming Function Blocks and Features
Definition
Enter a number will equal the ratio that the ratio control loop
will maintain between its process variable and a "wild
variable." The wild variable may be the Output Value of any
analog input or calculated value function block over which the
ration loop will have no control
The RATIO SETPOINT menu choice is essentially a
multiplier applied to the wild variable's value. This
multiplication's result will be a working set point for the loop
that will ensure the desired "process variable-to-wild variable"
ratio. For example, suppose you intend to use the ratio
control loop to maintain a 50 % fuel-air ratio in the operation
of a furnace. If the loop will be directly controlling air flow (i.e.
- air flow will be the loop's process variable) and fuel flow will
be used as a wild variable to generate the ratio loop's
working set point, the RATIO SETPOINT menu choice will
have to be set to 0.50. Hence, if fuel flow is measured to be
60, the working set point that will be used in the ratio loop's
control of air flow will be (60) x (0.50) = 30.
To make a ratio control loop's working set point equal to the
product of RATIO SETPOINT and a specific wild variable
value, the loop's working set point must be toggled to SP2
using the "SP (Set Point Select)" key while viewing the loop's
ON LINE display. Refer to Figure 4-1.
When the DISCR VS KEY SEL discrete is ON (1) this
parameter takes the place of the On-Line Tune Loop menu's
Toggle Setpoint Source prompt.
SETPOINT SELECT = ON (1) = Setpoint2
SETPOINT SELECT = OFF (0) = Setpoint1
When DISCR VS KEY SEL is OFF (0), SETPOINT SELECT
has no effect.
Setpoint #1 and #2 are independent setpoints. Either may be
the active setpoint for the loop. When viewing a live ON
LINE mode control loop display, a loop may be switched
between SETPOINT #1 and SETPOINT #2 by accessing the
Tune Loop menu and selecting TOGGLE SETPOINT
SOURCE. Operation of the loop using SETPOINT #1 will be
indicated by the presence of an "SP1" symbol on the loop's
display. "SP2" will be the symbol observed when the loop is
operating using SETPOINT #2.
While SETPOINT #2 may be programmed as a numerical
value, it may also be used as a remote set point input to the
loop. You may link SETPOINT #2 to any of several analog
parameters that include the Output Values of analog input or
calculated value function blocks. If used as a remote set point
input, SETPOINT #2's value may not be manually changed
from within any live ON LINE mode control loop displays.
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