3.4 Cascade control of reflow ovens
3-13
Typical Control
Examples
3.4 Cascade control of reflow ovens
Cascade control is used to reduce the effects of disturbances in the manipulated system (disturbances in
the secondary loop) by adding a second PID loop to the regular PID loop.
Cascade control is also used in situations where a sensor is added close to the object to improve control
performance.
■ Application
Conventional temperature control of reflow ovens is performed using
only a sensor installed near the heater. In lead-free reflow ovens, the
melting temperature of solder is higher, and in order to minimize heat-
induced deterioration of the electronic components, a second sensor is
added inside the oven near the board to enable a higher precision of
temperature control.
• A thermocouple or platinum resistance temperature
input sensor can also be directly connected to input 2
(previously input 2 only supported 4 to 20 mA or 1 to 5
V, and an external converter was required).
• Auto tuning is now possible in both the cascade closed
and cascade open states.
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