This forum uses cookies
This forum makes use of cookies to store your login information if you are registered, and your last visit if you are not. Cookies are small text documents stored on your computer; the cookies set by this forum can only be used on this website and pose no security risk. Cookies on this forum also track the specific topics you have read and when you last read them. Please confirm that you accept these cookies being set.

PID in FB editor
#1
I am using the PID function in FB editor but it is not calculating a value for valve opening. Anybody experienced this before?
Reply
#2
As far I know FB PID is based on our script version. Have a read trough these threads and it should help you to debug it.
https://forum.logicmachine.net/showthrea...0#pid20270
https://forum.logicmachine.net/showthrea...1#pid20501
------------------------------
Ctrl+F5
Reply
#3
I get no output at all. I also removed the PID in FB editor and tried with this info https://openrb.com/example-pid-thermostat-with-lm2/

added the PID to the User Libraries 
Code:
PID = {
  -- default params
  defaults = {
    -- invert algorithm, used for cooling
    inverted = true,
    -- minimum output value
    min = 0,
    -- maximum output value
    max = 100,
    -- proportional gain
    kp = 0.25,
    -- integral gain
    ki = 0.42,
    -- derivative gain
    kd = 0.1,
  }
}

-- 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


and added the following script to the Resident Scripts
Code:
-- init pid algorithm
if not p then
  p = PID:init({
    current = '2/2/8',
    setpoint = '32/1/58',
    output = '32/1/58'
  })
end

-- run algorithm
p:run()

But my output stays 0.

I want to control a 3 way valve at the output to get a stable temperature at the valve for cooling. 
Current is the measured flow temperature
Setpoint the requested flow temperature
and Output is 0-100% (0-10V)
Reply
#4
Your setpoint and the output is same group. For PID to work it must be live device with real feedback.
------------------------------
Ctrl+F5
Reply
#5
(18.06.2021, 07:46)Daniel. Wrote: Your setpoint and the output is same group. For PID to work it must be live device with real feedback.

OK, that was the problem, live feedback was already there as it runs to a selector (different PID in cooling and heating)

The problem is in the fact it can't be a virtual object. 
Still in FB editor it won't work.
Reply


Forum Jump: