Bang Bang- Disabling PID for resistor heater block

How do i do this in the firmware.

Are there benefits to using PID, even with a heater block?

If you tune it well then, yes it will give a more steady temperature, but will take a little longer to warm up. If it is not tuned it may never reach the target temperature or may oscillate wildly.

The advantage of bang bang is that it needs no tuning and it heats up at maximum speed. The downside is that it always oscillates around the set point. With my heater designs it only oscillates about +/- 1 or 2C. It seems most people fail to get that close with PID.

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[www.hydraraptor.blogspot.com]

... i think i've found an interesting approach for combining the 'instant powerup' of the "bang-bang" with PI or PID.

When starting the controller (or if the temp-difference is more than say 20°C), the controlling is disabled and the heater runs at full power.

When the temp. comes in a specified range near the target temperature (in our sensors it's +/- 0.5°C around the target temp of 60°C), the controlling is enabled again.

With a PI-algorhythm controlling a DAC which drives two 20Watt-heaters we control the temperature of a steel-armature with an accuracy of +/- 0.001°C at the sensor position

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Viktor
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