Siemens SIMATIC S5 Manual

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Special Functions for Plastic Machines4–73IP244C79000–B8576–C860–023 Special Functions for PlasticMachines3.1 Hot Channel Control3.1.1 IntroductionThe heating cartridges used in hot channel control are extremely sensitive to fast temperaturechanges. To handle this characteristic, an ”approach phase” was developed.The system time constants involved when using these heating cartridges are small compared withthose encountered using heating collars. The sampling time must therefore be kept as short aspossible.3.1.2 Approach PhaseUntil the actual value (actual value = approach setpoint (SWA) – start-up zone (ZA)) is reached, auniform manipulated variable S is set for all controllers, e.g. 25% (no closed-loop control).Once the value reaches the approach zone, the approach time t AZ is started and the approachsetpoint is used during this time. When the start-up time tAZ has elapsed, the temperature setpointthen becomes valid. If, during operation, the actual value sinks below the value = approach setpoint(SWA) minus zone (Z A) the approach procedure is restarted.") #! &# !# "# #")#! &# !"# # #$# !#$!%$! ( ! "# #! ## ! #" # # # ! " " # "" '#" ) #!&# ! $#%! Fig. 3.1.2/1 Approach phase for hot channel control# #!!" ' ' $! " )"# #!!")#$ " # ""