dev = DeviceOpen["Serial", "COM4"]

parseData[{val1__, 9, val2__, 9, val3__}] :=
 ToExpression@FromCharacterCode@# & /@ {{val1}, {val2}, {val3}}
parseData[___] := Sequence[]

rawReadings = {};
task = SessionSubmit[
  ScheduledTask[
   AppendTo[rawReadings,
    Flatten[{Now,
      DeviceReadBuffer[dev, "ReadTerminator" -> 10]}]], {1, 20},
   "AutoRemove" -> true]]

ListLinePlot[Transpose[parseData /@ rawReadings],
  PlotLegends -> Automatic] // Dynamic

DeviceClose[dev]