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α
2 Simple Application Controllers
6.22.6 PID Troubleshooting
For some systems, the Parameter values derived from the Auto-tuning process will be less
than optimal. If Auto-Tuning derives such parameter values, the user should refer to the
descriptions above for each relevant parameter (K
adjust these parameters.
Response when K
The PV rises slowly, stabilizes slowly with no overshoot.
Response when T
The PV stabilizes slowly with less searching (overshoot and undershoot) for the SV.
Response when T
The PV stabilizes quickly. There is more searching (overshoot and undershoot) for the SV.
6.22.7 Error Codes
Error Codes are reported by the PID Function Block via the string output pin. The error code
byte consists of 8 error flags, but only the lower 6 bits are functional. An error code value of
zero means there is no error.
Table 6.30:
Bit
Content
b0
Sampling time < (system) scan time
Filtered PV change overflow
b1
(∆PV
b2
Deflection overflow (EV < -32768 or EV > 32767)
b3
Integration result overflow (out of range: [-32768, 32767])
b4
Derivative overflow (out of range: [-32768, 32767])
*2
Internal error during auto-tuning operation
b5
*1. This is the maximum change in PV when the input filter is 0%. In the case of a higher input
filter, the maximum change in PV can be higher.
*2. Bit 5 of the error code is set when the calculated PID parameters are out of range. Bit 5 is
not set when AT is stopped by the user.
Setup of the PID Function Block directly from the
1 ) Allocate the input pin to be used for the function block.
2 ) Press the "OK" key with the cursor in the function block. The function block edit screen is
displayed as shown.
3 ) Press the "OK" button to setup the parameters for the PID function block.
is decreased:
P
is increased:
I
is increased:
D
< -21692 or ∆PV
> 21692)
fn
fn
, T
, and T
P
I
D
*1
α
2 Series Controller
Function Blocks 6
) or see the following guide to
State of processing
PID operation continued
AT ends
B 0 0 1 : P I
D
S e t u p
F
C h a n g e
D e l e t e F B
B 0 0 1 : P I
D
S e t
V
a
P r o c e s
S a mp l e T i
6 - 64
B
N o
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s
V
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