Sampling time (T) : is the time to sample the feedback value. In eachs ampl ing period thecontroller
runs one time.The l onger the sam plingt ime, the sl ower the r esponding.
PID c ontroldiscr epancy limit:t he allowable maximum discrepancy o f PID sys tem outputvalue re lative
t othe cl osed-loop as sign ed value.Asshown in following diagram, w ithin the discrepancylimit, PID
controller stops adjustment. Properlysetting t his function code can improve t he accuracy and stabilit y of
PIDsystem.
Feedback disconnected detecting value:this detecting valueis relative to the full range (100%) .
The systemdetects the P ID feedback valueall the time.When thefeedback value is less orequal to the
feedbackdisconnected detecting value,the syst em s tarts to time the detection.When the detecting time
exceeds thef eedbac kdi sconnected detect ing time, the system will s end an a lert offeedba ck disconnecting
failure .(E02E)
Fig. 6-19Coi ncidenc e relation of discrepa ncy limit and output frequency
Feedback
Assigned
Value
Discrepancy Li mit
Output f
Time t
Time t
F4.25
Samplingcycletime(T)
0.01 99.99 s
～
0.10s
F4.2 6
P ID c ontrol
di sc repanc y li m it
0.0 100.0%
～
0.0 %
Fu nction
Code
Name
Setting Rang e
Default
Value
F4.27
Feedb a ck di sconn ection
de t e cting value
0.0 100.0%
～
0.0 %
F4.28
Feedb a ck di sconn ection
detecting t ime
0.0 360.0s
～
1.0 s
Fu nction
Code
Name
Setting Rang e
Default
Value
Chapter 6 Parameter D escripti on
DZB Series
-62-
Proportional gain (K p): det ermi nesthe adjusting strength of PI D adjustor. T hebigger the P, the bigger
the a djus ti ng st reng th is. This para m e te r be ing 100 means tha t wh en th e d iffer e n ce betw ee n the PID
fee dback value a nd the assi gnedvalue i s 100%, the adjustingrange of PID a djus torto the output freque ncy
command isthe m axi mum frequency ( ignore i ntegralaction a nd derivativeaction).
Integrating ti me (Ti): determi nesthe speed at which PID adju stor performs integral regu lat ion to the
discre pancy betweenthe PIDfeedbackvalue and t he assigned value.The Tiis indicati ng the per iod of time
tha t integral contr oll er (ignore proporti onala ction and derivative action),when the discrepancy between
the PID feedba ck value and the assigned va lue i s 100%, continuously re gulates to make the regulating
amou ntto reach the m axi mum frequency ( F0. 047).The shorter the i ntegra tingtime,the st ronger the
ad justing strength i s .
Differenti al time (T d): determi nes the contr ollingstrengtha t whichPID adjustor pe rforms adjustment
to the va r ia nce r atio of d i scre pa n cy be tw een th e PI D feedback value an d the a ssi g ned va lue. TheTd is
indi catingt he period of time w ithin whi ch if the fee dback value is chang ed 100%, t he regulating amount
of integral controlleris the maximum frequency (F 0. 04)(i gnor e proporti onalaction and integral action).
The longe rthe Td ,the bigger the c ontrolling s trengthis.PID is the most popularl y used cont rolmode in
process control,with ea ch part pl aying different role.Following simplyintroducesthe operational
principle and the controlling method:
Proportion cont rol (P): when thereis dis crepa ncy betweenfeedbackand the assignment,output t he
regul ating amount in proporti onto the discrepancy.If t he discrepancy is c onstant, the regulating amount
kee ps constant. Pr opo rt ion c ontrol can res ponsequickl yto the feedback va ria tion,butonly u sing
proportion control is unabl e to perf ormnoncorrespondi ngcontrol .The b iggerthe proportional gain, the
fast er the s ystem regulating speed, but being too bigma ycause os cillation. The control methodis first to
seta long int egratingtime and a zero differ entialtime, and then run the s ystem only byusing proportion
cont rol. Change the assigned value,and wa tch the stablediscrepancy(steady-stat e error)of feedback
signal andassigned value. If the s te ad y-stateerror isat the varying directi on ofassigne d value(for
instance, i ncrease the assigned value, the feed back value after the system is st eady is always less than the
as signed value),continue to increase theproportional gain, otherwise decrease it.Repeat t he above until
the ste ady- st a te e rror is relativ e ly s m all (i t is v ery d iffic ult t o do n o steady-s ta te er r or).
Integral t ime(I): when there is a discrepa ncy between the feedbac k and assignment, continuously
acc um ulate t he o ut pu t regu l a tion a m ou nt. I f th e discr e p ancy s ti ll e xists, co ntinu e to increase the reg ula ti o n
amou ntuntil ther e is nodi screpancy. I nte gralcontrollercan e ffectively eliminatet hesteady-stateerror.
Integral controller being too strong can cause repeated overs hooti ng, system unstable a ndup tilloscillati ng.
The characteri sti c ofoscillation c aused b ytoo strong integral actionis t hatt he feedba ck signal i s swinging
up and downaround the assigned value,and the amplitude ofswing inc reases graduallytill theoscillation
happens. Normally th e integral timeis adjusted frombigt osmall, gradually regulate the integral time, and
wa tch the effec t, until the system stable speed meet sre quirements.
Differentialtime (D): whenthediscrepancy betweenfeedback and assignment varies,output a regulation
amount i n pro portion to the v arianc e r atio of di scr epancy. The regul ation a mount is r e lated t o t h e dire ct ion
and magnitude of discrepa ncyvariation, but irrel evant to the direction and value of the d iscrepancy itsel f.
The differential contr olactioni st o per formthe c ontrol according to the va ryingtrend whe n the feedback
signal variationhappens, and ther ebyto restra in the feedback signal va riation. It should be c aution to use
dif fere nti alcontrolle r a s the di ffer ential controlhave a trend tomagnify the system i nterference , especiall y
the high varyingf requencyinterference.
Chapter 6 Parameter Descr iption
DZB S eri es
-61-
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