IDEC MicroSmart - Manual (Page 369)

21: PID I NSTRUCTION
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Source Operand S4 (Process Variable before Conversion)
The PID instruction is designed to use analog input data from an analog I/O module as process variable. The analog I/O
module converts the input signal to a digital value of 0 through 4095, and stores the digital value to a data register depend-
ing on the mounting position of the analog I/O module and the analog input channel connected to the analog input source.
Designate a data register as source operand S4 to store the process variable.
For example, when the analog I/O module is mounted in the first slot from the CPU module among all analog I/O modules
(not including digital I/O modules) and when the analog input signal is connected to analog input channel 0 of the analog
I/O module, designate D760 as source operand S4. When the analog input is connected to analog input channel 1 of analog
I/O module No. 3, designate D806 as source operand S4. For details about data register allocation numbers for analog I/O
modules, see page 24-8.
Allocation Numbers for Source Operand S4
When an analog I/O module is not used for supplying data to source operand S4, make sure that the S4 data takes a value
between 0 and 4095. When S4 stores a value larger than 4095, the process variable is set to 4095.
Destination Operand D1 (Manipulated Variable)
The data register designated by destination operand D1 stores the manipulated variable of –32768 through 32767 calcu-
lated by the PID action. When the calculation result is less than –32768, D1 stores –32768. When the calculation result is
greater than 32767, D1 stores 32767. While the calculation result is less than –32768 or greater than 32767, the PID action
still continues.
When the output manipulated variable limit is disabled (S2+2 set to off) while the PID action is in progress, the data regis-
ter designated by S1+1 holds 0 through 100 of the manipulated variable (D1), omitting values less than 0 and greater than
100. The percent value in S1+1 determines the ON duration of the control output (S2+6) in proportion to the control
period (S1+13).
When the output manipulated variable limit is enabled (S2+2 set to on), the manipulated variable (D1) is stored to the out-
put manipulated variable (S1+1) according to the output manipulated variable upper limit (S1+16) and the output manipu-
lated variable lower limit (S1+17) as summarized in the table below.
While manual mode is enabled with the auto/manual mode control relay (S2+1) set to on, S1+1 stores 0 through 100 of the
manual mode output manipulated variable (S1+18), and D1 stores an indefinite value.
While auto tuning is in progress, S1+1 stores 0 through 100 of the AT output manipulated variable (S1+22), and D1 stores
an indefinite value.
Examples of Output Manipulated Variable Values
Channel
Analog I/O Module No.
1 2 3 4 5 6 7
Analog Input Ch 0 D760 D780 D800 D820 D840 D860 D880
Analog Input Ch 1 D766 D786 D806 D826 D846 D866 D886
Output Manipulated
Variable Limit Enable
(S2+2)
Output Manipulated
Variable Upper Limit
(S1+16)
Output Manipulated
Variable Lower Limit
(S1+17)
Manipulated Variable
(D1)
Output Manipulated
Variable
(S1+1)
OFF (disabled) — —
≥ 100
100
1 to 99 1 to 99
≤ 0
0
ON (enabled)
50 25
≥ 50
50
26 to 49 26 to 49
≤ 25
25
10050 —
≥ 100
50
1 to 99 (1 to 99)
Ч 0.5
≤ 0
0