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PID algorithm questions - Printable Version

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PID algorithm questions - Novodk - 15.04.2023

Hi, I'm trying to setup underfloor heating with SE Valves

This is my setup/configuration, but I have some questions:

  1. Is this how it should be done?
  2. If I want to use GA 1/1/3 to indicate if the heating is On or Off with 1 bit 01.001 switching how can I do that?
  3. What if I want heating in more rooms? Do I just make a new Residential script and according Group Addresses?
  4. he Manual mode, it says that the PID algorithm is stopped when this object value is 1, is it stopped or just paused? Should I use it to stop heating if my window is open in that room?
  5. Again about the Manual mode, I have window switches connected to a knx binary input, and the way I use it is with 1bit - 01.009, so that it says Close(1) if the window is closed and Open(0) if the window is open, but thats reversed, how to fix that?

Group Addresses:

1/1/0 Test Room Setpoint Temp - (2 byte - 09-001 Temperature) - Temp setpoint visualization
1/1/1 Test Room Output Value - (1 byte - 05.001 scale) - SE Valve, Group Object: 0: Valve Actuating value - Drive to position
1/1/2 Test Room Actual Position - (1 byte - 05.001 scale) - SE Valve, Group Object: 2: Actual valve position - Indicate actual valve position
1/1/3 Test Room Heating On/Off - (1 bit - 01.001 switch) -
1/1/4 Test Room Window Contact - (1 bit - 01.009 open/close) - Binary input, Group Object: 0: Window open/close
1/1/5 Test Room Current Temp - (2 byte - 09-001 Temperature) - PIR with temp, Group Object: 11: Temperature sensor:Output


Scripting -> Common functions

Code:
-- PID init, returns new PID object
function PID:init(params)
  local n = setmetatable({}, { __index = PID })
  local k, v
  -- set user parameters
  n.params = params
  -- copy parameters that are set by user
  for k, v in pairs(PID.defaults) do
    if n.params[ k ] == nil then
      n.params[ k ] = v
    end
  end
  -- reverse gains in inverted mode
  if n.params.inverted then
    n.params.kp = -n.params.kp
    n.params.ki = -n.params.ki
    n.params.kd = -n.params.kd
  end
  return n
end
-- resets algorithm on init or a switch back from manual mode
function PID:reset()
  -- previous value
  self.previous = grp.getvalue(self.params.current)
  -- reset iterm
  self.iterm = 0
  -- last running time
  self.lasttime = os.time()
  -- clamp iterm
  self:clampiterm()
end
-- clamps iterm value
function PID:clampiterm()
  self.iterm = math.max(self.iterm, self.params.min)
  self.iterm = math.min(self.iterm, self.params.max)
end
-- clamp and set new output value
function PID:setoutput()
  local t, object, value
  self.output = math.max(self.output, self.params.min)
  self.output = math.min(self.output, self.params.max)
  value = math.floor(self.output)
  local t = type(self.params.output)
  -- write to output if object is set
  if t == 'string' or t == 'table' then
    if t == 'string' then
      self.params.output = { self.params.output }
    end
    for _, output in ipairs(self.params.output) do
      grp.write(output, value, dt.scale)
    end
  end
end
-- algorithm step, returns nil when disabled or no action is required, output value otherwise
function PID:run()
  local result
  -- get manual mode status
  local manual = self.params.manual and grp.getvalue(self.params.manual) or false
  -- in manual mode, do nothing
  if manual then
    self.running = false
  -- not in manual, check if reset is required after switching on
  elseif not self.running then
    self:reset()
    self.running = true
  end
  -- compute new value if not in manual mode
  if self.running then
    -- get time between previous and current call
    local now = os.time()
    self.deltatime = now - self.lasttime
    self.lasttime = now
    -- run if previous call was at least 1 second ago
    if self.deltatime > 0 then
      result = self:compute()
    end
  end
  return result
end
-- computes new output value
function PID:compute()
  local current, setpoint, deltasc, deltain, output
  -- get input values
  current = grp.getvalue(self.params.current)
  setpoint = grp.getvalue(self.params.setpoint)
  -- delta between setpoint and current
  deltasc = setpoint - current
  -- calculate new iterm
  self.iterm = self.iterm + self.params.ki * self.deltatime * deltasc
  self:clampiterm()
  -- delta between current and previous value
  deltain = current - self.previous
  -- calculate output value
  self.output = self.params.kp * deltasc + self.iterm
  self.output = self.output - self.params.kd / self.deltatime * deltain
  -- write to output
  self:setoutput()
  -- save previous value
  self.previous = current
  return self.output
end

Scripting -> Resident -> PID Test Room (Sleep interval 10 seconds)

Code:
-- init pid algorithm
if not p then
  p = PID:init({
    current = '1/1/5',
    setpoint = '1/1/0',
    output = '1/1/1',
manual = '1/1/4',
min = '0',
max = '100',
kp = '1',
ki = '1',
kd = '1'
  })
end
-- run algorithm
p:run()


RE: PID algorithm questions - admin - 17.04.2023

1. Your PID library is incomplete. Copy it from here: https://openrb.com/example-pid-thermostat-with-lm2/
Don't put quotes around numbers, only around group addresses. You can remove min/max/kp/ki/kd settings from PID configuration if you are using the default values.

2. You can add an extra if into the script to check whether heating is enabled and window is closed. Remove manual = '1/1/4', from PID configuration.
Code:
if grp.getvalue('1/1/3') and grp.getvalue('1/1/4') then
  p:run()
else
  grp.checkwrite(p.params.output, 0)
end

3. You can have multiple PIDs in a single script (use different variable names for each). Or you can make separate script for each PID. There's no big difference unless you need more than 10-20 PIDs. See this: https://forum.logicmachine.net/showthread.php?tid=2920

4. The manual mode does not turn off the output. It just stops the PID algorithm. Script in nr.2 sets output to 0 when either the heating is disabled or a window is open.