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In general several methods could be used for TEC control.
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Pulse Width Modulation |
Pulse width modulation (PWM) is a pulsed current with fixed amplitude and
variable duty cycle . Pulse width modulation essentially controls the duty
cycle as well as the frequency of the power applied to the TEC.
Averaged current delivered by PWM to controlled object
is estimated as equivalent of DC current of the same value.
It is true
for many applications, but is a great mistake in a case of TECs.
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Relay (On/Off) Control |
Relay (On/Off) is the simplest and most crude technique for controlling the
temperature. This method of control is the least preferred.
Because the power to the TEC is cycled from full ON to full OFF, thermal
cycling of the TEC will occur. It leads to ripples of stabilized temperature
and to degrade the life of the TEC unit.
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DC Closed Loop |
Among them - Proportional, Proportional-Integral (PI) Control or
Proportional-Integral-Derivative (PID) Controls.
In
proportional controllers there is always a residual error, even after the
controller has settled to the final state. This error is proportional to the
difference between the set-point temperature and the ambient temperature.
The residual error present in the proportional controller can be eliminated
by the addition of an integrator. PI control is required for systems that
have wide variation in either or both the thermal load and ambient
temperature.
Full PID control loops are the most complex and are less common. The PID
controller adds a derivative circuit to the PI controller which improves the
transient response.
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