Description of the regulation functions
PWM Function
General
Operating principles
The PWM function supports regulation of a pulse width on a TOR output. It is a function that formats the PID’s output.
The pulse width depends on the PID’s output (The PWM function’s INP input) and the modulation period.
The circuit diagram of the function’s operation is as follows:
PV
PID OUTP INP
PWM PW_O
SP
T_MOD
Note: The description of the parameters used is presented in the (See Programming
the PWM function, p. 368) module.
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TLX DS 37 PL7 xxE
Pulse widths
Description of the regulation functions
To each TOP of the T_MOD modulation period, the activation period in 10
-3
second of the PW_O output is calculated according to the following formula:
State 1 of the gap (shown in 10
-2
seconds) = INP * T_MOD / 1000
The following timing diagram illustrates this formula:
PW_O
Modulation period
50% 75% 35%
Time
Width of pulse
Practical rules T_MOD = TS (where TS is the sampling period of the upstream PID),
The period of the current task (expressed in 10
-3
second) is equal to:
(Required resolution)* 10 * T_MOD .
The PID is in the MAST task, the MAST’s period is 50*10
-3
s, TS = 500*10
-2
s and the required resolution is 1/50 (a T_MOD period must contain at least 50 periods of the current task).
T_MOD = TS = 500.
The period of the task where the PWM is introduced must therefore be less than 500
* 10 /50 =100 10
-3
s.
The PWM function can therefore be programmed in the MAST task. the resolution will be 1/100.
TLX DS 37 PL7 xxE
367
