User Guide - Eurotherm Ltda

nanodac RECORDER/CONTROLLER: USER GUIDEB2.6.6 Power Feed ForwardPower feed forward is used when driving an electrical heating element. It monitors the line voltage and compensatesfor fluctuations before they affect the process temperature. The use of this will give better steadystate performance when the line voltage is not stable.It is mainly used for digital type outputs which drive contactors or solid state relays. Because it only has valuein this type of application it can be switched off using the parameter ‘Pff En’. It should also be disabled forany non-electric heating process. It is not necessary when Eurotherm analogue thyristor control is used sincecompensation for power changes is included in the thyristor driver.Consider a process running at 25% power, with zero error and then the line voltage falls by 20%. The heaterpower would drop by 36% because of the square law dependence of power on voltage. A drop in temperaturewould result. After a time, the thermocouple and controller would sense this fall and increase the ON-TIME of the contactor just enough to bring the temperature back to set point. Meanwhile the process wouldbe running a bit cooler than optimum which may cause some imperfection in the product.With power feed forward enabled the line voltage is monitored continuously and ON-TIME increased or decreasedto compensate immediately. In this way the process need never suffer a temperature disturbancecaused by a line voltage change.‘Power Feed forward’ should not be confused with ‘Feed forward’ which is described in section B2.6.8.B2.6.7 Cool TypeCooling methods vary from application to application. For example, an extruder barrel may be cooled byforced air (from a fan), or by circulating water or oil around a jacket. The cooling effect will be different dependingon the method. ‘Cool Type’ (appears only if the ‘setup’ parameter ‘Ch2 Control’ is set to ‘PID’) isused to accommodate different types of cooling methods as follows:LINEARThe cooling algorithm may be set to linear where the controller output changes linearly with the PID demandsignal.OIL COOLING‘Cool Type’ = ‘Oil’. As oil is, to all intents and purposes, non-evaporative, oil cooling is pulsed in a linearmanner.WATER COOLINGIf the area being cooled is running well above 100°C, then the first few pulses of water flash into steam givinggreatly increased cooling due to the latent heat of evaporation. When the area cools, less (or even no) evaporationtakes place and the cooling is less effective.Setting ‘Cool Type’ to ‘Water’ delivers much shortened pulses of water for the first few percent of the coolingrange, when the water is likely to be flashing into steam. This compensates for the transition out of the initialstrong evaporative cooling.FAN COOLING‘Cool Type = ‘Fan’. Fan cooling is much gentler than water cooling and not so immediate or decisive (becauseof the long heat transfer path through the process mechanics). With fan cooling, a cool gain settingof three upwards is typical. Delivery of pulses to the blower is non linear, this non-linearity being caused bya combination of forced air movement and fan efficiency as a function of air velocity (e. g. the efficiency of afan when producing a low speed (laminar) air flow is different from its efficiency when producing a highspeed,turbulent flow.Appendix BPage 322HA030554Issue 7 Nov 12