ABB Ability 800xA Series, Operation

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Single Loop Automatic Operation with Ratio and Bias Section 8 Operation Examples
198 3BUR002418-600 A
Single Loop Automatic Operation with Ratio and Bias
A setpoint bumpless transfer is possible when the balance mode is enabled and the
system can manipulate the ratio and/or bias to prevent process bumps. These
configurations calculate a ratio or bias value that balances the remote setpoint with
the local setpoint upon a switch from local to remote setpoint.
Using auto bias, a switch from local to remote setpoint will cause the bias value to
automatically adjust to the difference between the active setpoint and the remote
setpoint times the ratio value. For example, if the active setpoint is 170.00 and the
remote setpoint is 200.00 with a ratio of 2.00, then the auto bias value will be:
-230.00 = 170-(200*2).
Using auto ratio, a switch from local to remote setpoint will cause the ratio value to
automatically adjust to the ratio between the active setpoint minus bias and the
remote setpoint. For example, if the active setpoint is 170.00 and the remote setpoint
is 200.00 with a bias of -230.00, then the auto ratio value will be:
2 = (170- (-230))/200.
The loop is in auto with a local setpoint and
with local bias.
Adjust the bias value in the Bi field to change the active
remote setpoint by the local bias value.
The new setpoint appears in the SP field.
Adjust the ratio value in the Ra field to change the active
remote setpoint by the local ratio value.
The new setpoint appears in the SP field.
Use the remote (REM) button to switch from
local to remote setpoint.
Bias value automatically adjusts to balance
remote and local setpoints.