That's correct. A PID, at least the type generally used for e-Brewing, only turn the element 100% on or off. As the set point is reached you will see it cycle on and off frequently. There is another form of ssr called an ssvr that can be used for controlling power to the element. That is probably what the Aubers power regulator uses.
Most PID's used in brewing use a form of Pulse Width Modulation (PWM), where the pulse being modulated is the gating control signal, not the output waveform. The typical minimum pulse cycle times are usually 1 second (MyPin's) or 2 seconds (Auber PID's). If we look at a 1 second cycle, then at a 25% gate pulse width is 0.25 seconds, and this would turn the power on for 0.25 seconds, and off for 0.75 seconds. In 0.25 seconds you get 15 power cycles out of the 60 that are available in the 1 second cycle time. This means power is on for 15 cycles, then off for 45 cycles, on for another 15 cycles, etc. With this form of power control the power delivered is linear with the power control setting (i.e. if you set the control at 25%, you get 25% power.)
SSVR's use a different type of pulse width modulation, called Phase Angle Modulation, where the pulse cycle time is 1/2 the AC power cycle time (for 60 Hz power, the pulse cycle time would be 1/120 second.) In phase angle modulation, the power is turned on for a portion of each AC half cycle. The on-time in each half cycle is linear with the control setting, but since the voltage varies from 0 to max back to 0 in each half cycle, the power delivered is not linear with control setting. At a setting of 25% you get less than 25% power, at 50% setting you get 50% power, and at 75% setting you get more than 75% power. And finally, SSVR's create more electrical noise since they do not employ 0 voltage turn on, whereas the other power modulation modes do.
Here are some example Phase Angle Modulation voltage waveforms:
The Auber EZBoils (DSPRxxx) controllers use a form of pulse count modulation that is referred to as Burst Mode Control. It turns on the power for full cycles, but varies the number of cycles turned on out of 100 cycles. At 25% power setting, it turns on for 25 AC cycles and off for 75 cycles. However, instead of being 25 on and then 75 off, it is 1 on 3 off, repeated 25 times. Compare this to the 15 on followed by 45 off cycles provided by the 1 second cycle time PWM. The effective pulse cycle time for the Burst Mode control is 1/15 second, so it provides more even heating than the PWM.
Brew on
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