Question of pid-contorl on stepwise configuration

[James Feist]

On 8/21/2019 4:36 AM, Derek Lin23 wrote:
> Hi team:
> 
>            I have a question regarding stepwise configuration on 
> pid-control.
> 
>            I have mine setup like below.
> 
>                                         {
> 
>                      "name": "Ambient_Temp",
> 
>                      "type": "stepwise",
> 
>                      "setpoint": 0.0,
> 
>                      "inputs": ["Ambient_Temp"],
> 
>                      "pid": {
> 
>                          "samplePeriod": 1.0,
> 
>                          "positiveHysteresis": 0.0,
> 
>                          "negativeHysteresis": 0.0,
> 
>                          "isCeiling": false,
> 
>                          "reading": {
> 
>                              "0": 25,
> 
>                              "1": 30,
> 
>                              "2": 35
> 
>                          },
> 
>                          "output": {
> 
>                              "0": 15,
> 
>                              "1": 15,
> 
>                              "2": 15
> 
>                         }
> 
>                      }
> 
>                  }
> 

I don't use the json configuration, so you'll have to do a bit of a 
comparison of apples and oranges, but here is an example of a stepwise 
configuration: 
https://github.com/openbmc/entity-manager/blob/08a5b175eec81c53506709fda8a7c168748cc22d/configurations/R1000%20Chassis.json#L577

Reading is the reading of the sensor, and output is the setpoint given 
to the fan pid. Depending on how you configure your system this can 
either be a percent, or it can be a tach reading. When a sensor reaches 
a reading, the corresponding output is given to the fan controller as a 
setpoint. So it my example, when we reach a temp of 30 degrees, the 
setpoint of 60 is given to the fancontroller. This 60 is unitless and 
depends on how the fan controller configuration is implemented how it 
affects the fans.

-James

>            And, I would like to know the meaning of each field, as far 
> as I understand from phosphor-pid-control, “setpoint” seems not used if 
> PID type is stepwise. Is that true? The “reading” field indicates the 
> temperature reading from the sensor “Ambient”. The “output” field should 
> indicate the duty % corresponding to the fans, or should output be RPMs? 
> That gives me when a reading of 25 degree(whatever the unit is), the 
> output duty of fans should set to 15%, or set to corresponding RPMs.
> 
> Do I understand the fields correctly?
> 
> Thank you,
> 
> ------------------------------------------------------------------------
> 
> *Derek Lin*
> Sr. BMC Engineer
> 8F,66, San Chong Rd., Nankang Software Park, Taipei.
> Lenovo Taiwan
> 
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> Phone+886281707411
> Emaildlin23 at lenovo.com <mailto:dlin23 at lenovo.com>
> 
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