GE CGA 351, User Manual

Page: 14 / 133

December 2004
1-6 General Information
The Heater Control
Circuit
The oxygen sensor temperature in the CGA 351 is maintained by a
heater, which is part of a complex temperature control loop. This
circuit constantly monitors the oxygen sensor temperature, compares
it to the set point temperature (700°C), and turns the heater ON or
OFF accordingly. The specific type of control circuit, a Proportional
Integral Derivative (
PID ) loop, is used because of the adjustable
parameters involved:
•
Proportional Band: Because the system cannot respond
instantaneously to temperature changes, the actual temperature of
the oxygen sensor oscillates about the set point. In general,
increasing the proportional band reduces the magnitude of these
temperature oscillations.
•
Integral Action: A consequence of increasing the proportional
band is the introduction of an offset between the set point and the
control point. The integral portion of the control loop acts to move
the control point back toward the set point within a specified
period of time. Decreasing this integration time reduces the offset
more quickly.
Note:
A third parameter, Derivative Action , is not used with the
CGA 351.
The heater control circuit is configured at the factory for optimum
performance. Because of the strong interaction between the
parameters involved, properly setting up the PID loop is a very
complex matter. As a result, randomly changing the P, and/or I
parameters can seriously degrade the performance of the CGA 351.
IMPORTANT:
Always contact the factory before attempting to
change the default P and/or I values. The submenu
for performing these changes is password protected
to prevent accidental changes.
www.DataSheet4U.com
www.DataSheet4U.com