Hot runner controllers are specialized temperature controllers that keep specialized injection-mold components at the design temperature in order to keep the mold material flowing. They use several different control techniques. Limit control establishes set points that, when reached, sends a signal from the hot runner control to stop or start a process variable. Linear control matches a variable input signal with a correspondingly variable control signal. Feedforward control does not require a temperature sensor and provides direct control-compensation from the reference signal. Proportional, integral and derivative (PID) control requires real-time system feedback. PID control also monitors the error between the desired variable value and the actual value. Fuzzy logic is a hot runner temperature control technique in which variables can have imprecise values (as in partial truth) rather than a binary status (completely true or completely false). Hot runner controllers that use advanced or non-linear controls such as neural networking, adaptive gain, or emerging algorithms are also available.
Product specifications for hot runner controllers include: number of inputs, number of outputs, input types, output types, and number of zones. The number of inputs is the total number of signals sent to the hot runner controller. The number of outputs is the sum of all outputs used to control, compensate or correct the process. Input types for hot runner controllers include direct current (DC) voltage, current loops, analog signals from resistors or potentiometers, frequency inputs, and switch or relay inputs. Output types include analog voltage, current loops, switch or relay outputs, and pulses or frequencies. Some hot runner controllers can also send inputs or receive outputs in serial, parallel, Ethernet or other digital formats which indicate a process variable. Others can send inputs and receive outputs from information converted to an industrial fieldbus protocol such as CANbus, PROFIBUS®, or SERCOS. PROFIBUS is a registered trademark of PROFIBUS International.