6-13
• Auto-tuning always calculates the excess time and limit sensitivity of thread for
two limit cycles and calculates PID values using characteristics equations, then
automatically writes the results.
• The setup data C21 setting changes the upper and lower output limit used
during auto-tuning.
C21 setting of 1, 3 or 5 causes the lower output limit to be determined by
variable parameter PA09 and the upper output limit to be determined by PA10.
C21 setting of 2 or 4, lower output limit is off and the upper output limit is on.
• The point at which output reverses (lower limit ⇔ upper limit) during auto-
tuning is determined from the SP and PV values at AT startup as follows.
• Auto-tuning performed using a variable parameter PA08 setting of 3 or 4
causes auto-tuning to be performed on SP, PID parameters tP-A1 to tP-A7, in
order.
• Auto-tuning can be started by the AT key, external switch input and by
transmission. The AT LED flashes during auto-tuning.
• Auto-tuning terminates without writing PID constants and the AT LED goes off
when any of the following conditions occur.
• Operation is terminated by pressing of the AT key.
• Operation is terminated by an external switch input.
• Operation is terminated by transmission.
• Mode change occurs. (When the MANUAL mode is invoked; the READY
mode is invoked by setting PA08 to 1 or 2, the RUN mode is invoked by
setting PA08 to 3 or 4.)
• When PV goes outside the range.
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