Mitsubishi Electric a2 Series Programming Manual page 112

α
2 Simple Application Controllers
Derivative Time and Derivative Gain, T
proportional part of PID-control. For changes in the PV, the Derivative component will
supplement the P-control depending on the rate of change of the PV. Derivative Control initially
outputs a large corrective action which dissipates rapidly over time. The outcome is that the PV
reaches the SV more quickly and does not fluctuate as much as with PI-control. There are two
ways to adjust the Derivative control of the PID Function Block, Derivative Time (T
Derivative Gain (K
The default value for T
32767 (in 10ms units). For small values of T
values, there will be a short stablization time with some searching (overshoot and undershoot)
for the SV. The second parameter, K
adjusted manually. The default value for K
of 0 to 100%. Increasing K
to sharp changes in PV.
Figure 6.22c. Characteristic response for different T
PV
Sampling Time, T
T range from 1 to 32,767 (in 10ms units). The default value for T
S
Noise Filter, α
ignores noise from the input sensors on the input signal, PV. The coefficient can be adjusted to
a value ranging from 0 to 99%. Setting α
) to the PID calculations. The default value for α
= PV
nf
Auto-tuning Bias, AT Bias. This value is an offset applied to the SV during Auto-tuning. The
SV, plus the AT bias, is the threshold during Auto-tuning where the output is switched from on
to off. During the Auto-tuning calibrations, the MV will be turned OFF when the PV passes the
"SV plus AT bias" point and not the usual SV point (without AT bias). Refer to the Auto-tuning
section for more details. The allowable range for the AT bias is -32768 to 32767. The default
value for AT bias is 0.
Note:
In some cases, a physical limitation may make it undesirable for PV to exceed SV too greatly.
This feature is useful in those applications that require that the PV stay below (or above) the
actual SV. AT-Bias allows the user to offset the SV to a point where overshooting and
undershooting may occur without undesirable results.
Direction. The direction of the system refers to the response of the PV as the MV is applied. If
an MV is applied and the response of the PV is in the positive direction, the system is said to
be a "Reverse" type system. Whereas, if a the PV responds in the negative direction then the
system is a "Direct" type of system. The default setting for Direction is "Reverse."
). T can be set manually or automatically with the Auto-tuning function.
D D
is 100 (1 second) but can be set to any value within the range of 1 to
D
D
will make the D-control more responsive (shorter stablizaton time)
D
PI action (without derivative action)
T (PID action)
D1
T
D3
T (PID action)
D2
(PID action)
Set value (SV)
. T is the period of time between two measurements of the PV. Values for
S S
. The α
coefficient determines the level at which the PID Function Block
f f
and K . D-control acts together with the
D D
, D-control will have a small effect. For large
D
, cannot be set by the Auto-Tuning function and should be
is 50% but can be set to any value within the range
D
parameters
D
T
to 0% disables the filter and passes the raw PV (PV
f
is 50%.
f
Function Blocks 6
> T > T
D3 D2 D1
Response to sudden change in PV
Time
is 50 (500 ms).
S
6 - 58
) and
D
n