What is the difference between “Open” and “Closed” loop control?
Closed-loop uses a thermocouple to read the nozzle temperature and provide feedback to the controlling circuit. This effectively forms a control-loop of action and reaction – the output power is dependent on the temperature readings coming back from the sensor and regulated accordingly. Open-loop control has no regulatory feedback, it just outputs a manually set power value with no knowledge of what the resultant temperature is doing. Open-loop, in practice, takes much longer to settle to the desired temperature and is easily disrupted by injection, variations in the melt temperature, mold cooling etc.. However it is available as a quick fix if a sensing thermocouple fails. Closed-loop is much more responsive and adaptive. When coming up to temperature, a closed-loop zone will initially apply large amounts of power and then back off as it approaches the set point. In open loop the power level is set to the final lower level and it can take forever and a day to get up to molding tempera
In open loop, the ECU uses information from user defined inputs, such as the VE table, to set injector duty cycle, and will not automatically correct to match your target A/F ratio. In closed loop, the ECU will monitor the A/F and automatically adjust the injector duty cycle in order to meet the target A/F ratio. However, one must still tune the VE table to keep the correction percentage as low as possible due to correction limits set by the user.
