Xfr Function Block - Honeywell UMC800 Reference Manual

2.81 XFR Function Block

Description
The XFR label stands for Bumpless Analog Transfer Switch. This block is part of the Signal Selectors
category. It looks like this graphically on the Control Builder.
Function
Provide "bumpless" switching between two analog input values (X,Y) that is triggered by a digital input
signal (*SY). When switched, the output ramps to the new value at a specified rate.
The rate at which the output (OUT) changes to a switched value (Y or X) is set by YRATE and XRATE
configuration values, respectively.
• If SY is switched to ON, then: OUT changes to Y value at YRATE.
• If SY is switched to OFF, then: OUT changes to X value at XRATE.
• When OUT reaches the selected target input, OUT tracks the selected input (until SY
changes).
Input
X = First analog value.
Y = Second analog value.
SY = Switch to Y command digital signal
Output
OUT = Selected Value
Block Properties
Double click on the function block to access the
function block properties dialog box.
Block Order (Read Only)
You can change the assigned execution order
number by selecting "Execution Order" in the
"Configure" menu and arrange the order to suit
your control strategy.
Configuration Parameters
You must configure the XFR function block
parameters to the desired value or selection that
matches your operating requirements.
Table 2-68 describes the parameters and the
value or selection.
3/99 Function Block Reference Guide
Function Blocks
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