Industrial resistance furnaces are a common class of controlled objects with nonlinearity, large lag, and large inertia. They are widely used in sample melting in laboratories and in staged heating and cooling of workpieces in heat treatment. According to the process’s temperature-accuracy requirements, different types of PID regulator + SCR power controller combinations can hold temperature within the appropriate range.
For resistance furnaces that only need constant-temperature holding without temperature recording, a digital temperature-indicating regulator with PID plus an SCR power controller is enough: the instrument displays and regulates temperature, outputs a 0–10 mA DC signal to the thyristor voltage regulator or trigger board, and changes the thyristor conduction angle to adjust output power. This fully meets requirements with low investment, intuitive operation, and easy maintenance.
For complex systems demanding high temperature-control accuracy plus multi-point control and recording, small-computer control is ideal: a control system built from an ordinary PC and PCI-bus I/O modules can replace multiple digital temperature indicators, upgrading the equipment while remaining fully compatible with existing setups. A typical configuration uses a PCI-bus optically isolated 32-channel 12-bit A/D card (range set to 0–312.5 mV) to acquire thermocouple temperature signals, and a PCI-bus optically isolated 8-channel 12-bit D/A card for analog outputs.
