MercuryiTC
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Page 127
10.2.1 Description of the heater circuit
Microcontroller U24 outputs a demand signal to DAC U11. U11 converts this signal to a demand
voltage for the heater output, which is equal to the desired heater voltage divided by 20. This
voltage is fed to the linear amplifier which outputs the heater drive (0-40 V, 0-2 Amp).
The measured upper and lower heater voltages are divided by 20 and fed back to ADC U12.
U12 sends the resulting voltage back to the microcontroller U24.
The lower heater voltage signal passes to ground through a 0.1Ω
resistor. The voltage across
this resistor is equal to the heater current divided by 10. This voltage is also fed back to ADC
U12, which sends the resulting signal to microcontroller U24. U24 can thus calculate the power
dissipation in the heater, and adjust its heater demand signal accordingly.
The heater current and voltage/20 feedback signals are also passed to the linear amplifier.
The power for the linear amplifier is provided by a pulse-width modulator converter, controlled
by U24. The output of this converter is filtered and passed to the linear amplifier via a current
monitor. This current signal is passed back to U24 and also drives an overcurrent trip circuit. If
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