Appendix B PID- PID functions of the control-loop variables
Changing these properties is generally not needed and you only need basic knowledge to do this.
You have the possibility, if you want to experiment with this or develop setups. Create an external
experimental-loop for example with an extension cable to test safely.
Valid values for a control-loop:
Proportional value (P control)
The fan speed changes proportionaly to the temperature change. A proportional value 1.0 scales
the
speed range of a fan in a temperature range of 80ºC. The fan starts to work when the
nominal value is overrun and achieve its maximum speed at 100 ºC (20 ºC + 80 ºC = 100 ºC), if the
nominal value is for example 20 ºC. The maximum speed is achieved earlier, if the selected
proportional value is higher than 1.0. The temperature range of 80 ºC is enhanced in lower 1.0. A
proportional value of 0 deactivates the proportional controlling of the fan.
The proportional value can be calculated as follows:
Tmax: Temperature, at which the maximum speed should be achieved
Ts: Nominal value temperature
P = 80°C / (Tmax - Ts)
Integral value (I control)
The integral value of a regulator influence the fan speed dependending on the time. The longer is
the temperature over the setup nominal value, the faster the fan rotates. The maximum fan speed is
achieved after 10 minutes at the integral value of 1.0 and the measured temperature of 1 ºC above
the nominal value. At 1 ºC below the nominal value the fan will be switched off at latest after 10
minutes.
dT: Temperature deviation from nominal value in ºC without prefix (-/+)
t : Time to run through the complete speed range of the fan in seconds
I = 600 / (t * dT)
t = 600 / (I * dT)
dT = 600 / (I * t)
The maximum speed is achieved after 6 seconds at the maximum integral value of 100 and a
temperature of 1 ºC above the nominal value. An integral value of 0 deactivates the integral
controlling of the fan.
The calculation of integral value given above is simply an evidence for the time response at different
values, as the temperature does not last constantly above the nominal value practically and
changes the time response respectively. The integral value should be applied to “slow” control-
loops, e.g. for cooling hard-disc.
Differential Value (D control)
The differential value has an impact only on the speed of a fan, if the temperature changes.
Thereby the real temperature is insignificant, the temperature difference between 2 readings is
important. The bigger the temperature difference, the stronger the speed for this measuring interval
accelerated (or decelerated). If the fan speed does not maintain then on the new value, the integral
value should also be used always with the use of differential value. The differential value reacts then
as an acceleration factor for the integral controlling at rapid temperature changes. The differential
value should be used in “fast” control-loops, e.g. for cooling processors. A differential value of 0
deactivates the differential controlling of the fan.
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