Vacuum controllers monitor and control vacuum levels for process equipment such as vacuum furnaces, autoclaves, and coating machines. They provide stable and repeatable control of process chamber pressure for applications such as etching and thin-film deposition. A throttle valve and integral electronics control the pumping speed and provide consistent down-stream pressure control. The user interface consists of a digital front panel with a menu or keypad, or analog components such as knobs and switches. Computer-programmable, web-enabled, and network-ready vacuum controllers are also available. Often, these vacuum controls include a microprocessor or programmable logic controller (PLC). Vacuum controllers that interface to personal computers (PC) may include human machine interface (HMI) software or provide supervisory data acquisition and control functionality (HMI). A vacuum control that sends and receive commands via an industrial fieldbus protocol may use CANbus, SERCOS, or PROFIBUS® (PROFIBUS International).
Vacuum controllers can use linear control, limit control, PID control, feedforward control, fuzzy logic, or advanced (non-linear) controls. Linear control matches a variable input signal with a correspondingly variable control signal. Limit control is a type of on-off or bang-bang control that establishes set points or limits that, when reached, send a signal to stop or start a process variable. Proportional, integral, and derivative (PID) control requires real-time vacuum system feedback. Feedforward control provides direct-control compensation from the reference signal. Fuzzy logic is a vacuum control technique in which process variables can have imprecise values (as in partial truth) rather than a binary status (completely true or completely false). Advanced or nonlinear controls for vacuum controllers use algorithms such as neural networking and adaptive gain. Choices for vacuum controller functionality include: data logging, rate indication, and totalizing.
Selecting Vacuum Controllers
Selecting vacuum controllers requires an analysis of parameters such as form factor or mounting style, number of inputs, number of outputs, input types, and output types. Some vacuum controllers have a printed circuit board (PCB) form factor. Others are designed for mounting in a rack, on a wall, or with a DIN rail. Stand-alone vacuum controllers are benchtop or floor-standing units with a full-casing or cabinet and an integral interface. Vacuum control suppliers specify the number of inputs as the total number of signals sent to the vacuum controller. The number of outputs is the total number of signals used to control, compensate or correct the industrial process. Input types include: direct current (DC) voltages, current loops, analog signals from resistors or potentiometers, frequency inputs, and switch or relay inputs. Output types for vacuum controllers include analog voltages, current loops, switch or relay outputs, and pulses or frequencies.