Chapter 5 Temperature Measurement Module AH04PT/AH08PTG Control diagram: The instruction PID is inside the dotted line. 1/S 1/K I + + + 1/K G(s) - P + S K D The PID algorithm is as follows. ( ) dt t dE K dt t E K t E K MV D I P ) ( * ) ( t 0 + + = ∫ Forward action: ( ) ( ) ( ) t SV - t PV t E = Reverse action: ( ) ( ) ( ) t PV - t SV t E = b. Control mode Cyclic control mode: Users set a cycle according to a controlled environment. (If the ambient air temperature changes slowly, the cycle can be longer.) The width of a pulse is defined below.
Pulse width=Output value (MV)/(Maximal output value – Minimal output value)ЧCycle Users can set the width of a pulse and a cycle (sampling time) by means of the instruction GPWM. Example: The cycle is 2000 ms, the maximal output value is 100, and the minimal output value is 0. After the PID algorithm is performed, the output value gotten is 50. Width of a pulse=50/(100-0)Ч2000 ms=1000 ms Therefore, the pulse width used in the instruction GPWM is 1000 ms, and the cycle used in the instruction GPWM is 2000 ms. 5-11