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Release of AT in the Middle
To release AT in the middle, select OFF on the AT execution setting screen by the use of
key and press the
key.
NOTE:
In case AT is released in the middle, PID values are not changed.
Reasons Why AT Does Not Function
1) Control output is in manual mode.
2) The proportional band (P) of control output is OFF.
3) PV value (measured value) is in the state of scaleover.
4) On the keylock screen, No. 3 is selected. (AT is executed when it is turned ON before keylock setting.)
5) AT is suspended (RST).
If the following conditions arise while AT is in execution, AT is released:
1) Output is at 0% or 100% continuously for 200 minutes.
2) PV value gets scaleover.
3) RST input is received.
4) AT is terminated by key operation or through communication.
5) AT of PID No. 1 through No. 6 (No. 3 in the case of zone) has completed.
6-5. PID Action
P (Proportional action)
The ratio (%) of a range in which control output changes relatively to a measuring range is set. Output increases or decreases in proportion to difference
between PV value and SV value. The narrower the proportional band, the larger a change in output, i.e., the stronger the proportional action. Nonetheless,
an excessively narrow proportional band causes control to vibrate, resulting in control similar to ON-OFF action.
I (Integral time)
This is the function to correct an offset (constant deviation) produced in proportional band. The longer the integral time, the weaker the correcting action,
that is, reducing the integral time strengthens the correcting action but it may cause undulation of control results due to integral hunting.
D (Derivative time)
A change in control output is estimated and overshooting is suppressed to improve the stability of control. A longer derivative time strengthens derivative
action but it may cause control results to vibrate.
6-6. Manual Reset
In PID action, an offset is corrected automatically by I, i.e., integration. When OFF is set for I, however, this correction is not carried out and so output is
increased or decreased manually for correction. This method is called manual reset.
6-7. Output Lower Limit and Higher Limit Setting Limiters
Output limiter means to limit a minimum or maximum value of control output and this function is effective in securing the lowest temperature or
suppressing overshooting of control.
Output limiter gives preference to a lower limit value. When a larger lower limit value than a higher limit value is set, the higher limit value is forced to
become the lower limit value +0.1%. In other words, it is not possible to set a higher limit value which is less than a lower limit +0.1%.
6-8. Proportional Cycle Time
It can be set within a range from 1 to 120 seconds in the case of contact output or SSR drive voltage output. Proportional cycle time is ON time + OFF time
within a proportional band.
