21: PID INSTRUCTION
21-8 « FC4A MICROSMART USER’S MANUAL »
Example – Sampling period: 80 ms, Scan time: 60 ms (Sampling period > Scan time)
S1+13 Control Period
The control period determines the duration of the ON/OFF cycle of the control output (S2+6) that is turned on and off
according to the output manipulated variable (S1+1) calculated by the PID action or derived from the manual mode output
manipulated variable (S1+18). Set a required value of 1 through 500 to specify a control period of 0.1 sec through 50.0 sec
to the data register designated by S1+13. When S1+13 stores 0, the control period is set to 0.1 sec. When S1+13 is set to a
value larger than 500, the control period is set to 50.0 sec.
The ON pulse duration of the control output (S2+6) is determined by the product of the control period (S1+13) and the
output manipulated variable (S1+1).
Example – Control period: 5 sec (S1+13 is set to 50)
S1+14 High Alarm Value
The high alarm value is the upper limit of the process variable (S1+0) to generate an alarm. When the process variable is
higher than or equal to the high alarm value, the high alarm output control relay (S2+4) is turned on. When the process
variable is lower than the high alarm value, the high alarm output control relay (S2+4) is turned off.
When the linear conversion is disabled (S1+4 set to 0), set a required high alarm value of 0 through 4095 to the data regis-
ter designated by S1+14. When S1+14 stores a value larger than 4095, the high alarm value is set to 4095.
When the linear conversion is enabled (S1+4 set to 1), set a required high alarm value of –32768 through 32767 to the data
register designated by S1+14. The high alarm value must be larger than or equal to the linear conversion minimum value
(S1+6) and must be smaller than or equal to the linear conversion maximum value (S1+5). If the high alarm value is set to
a value smaller than the linear conversion minimum value (S1+6), the linear conversion minimum value will become the
high alarm value. If the high alarm value is set to a value larger than the linear conversion maximum value (S1+5), the lin-
ear conversion maximum value will become the high alarm value.
S1+15 Low Alarm Value
The low alarm value is the lower limit of the process variable (S1+0) to generate an alarm. When the process variable is
lower than or equal to the low alarm value, the low alarm output control relay (S2+5) is turned on. When the process vari-
able is higher than the low alarm value, the low alarm output control relay (S2+5) is turned off.
When the linear conversion is disabled (S1+4 set to 0), set a required low alarm value of 0 through 4095 to the data register
designated by S1+15. When S1+15 stores a value larger than 4095, the low alarm value is set to 4095.
When the linear conversion is enabled (S1+4 set to 1), set a required low alarm value of –32768 through 32767 to the data
register designated by S1+15. The low alarm value must be larger than or equal to the linear conversion minimum value
(S1+6) and must be smaller than or equal to the linear conversion maximum value (S1+5). If the low alarm value is set to
a value smaller than the linear conversion minimum value (S1+6), the linear conversion minimum value will become the
low alarm value. If the low alarm value is set to a value larger than the linear conversion maximum value (S1+5), the linear
conversion maximum value will become the low alarm value.
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