Temperature control method of induction heating equipment

The system control method of induction heating equipment can be open loop or closed loop. Open loop is the simpler of the two. In these systems, temperature control is obtained by finely adjusting heating input power, maintenance time (single-point induction heating) and fire feedback speed (induction heating scanning process). In this way each workpiece or each part of a workpiece receives controlled energy.

Closed-loop control systems are implemented using electrical signals generated by thermocouples or pyrometers that are connected to a special controller that compares the measured temperature with the temperature preset by the controller. The temperature difference is used to trigger power controllers and power regulators related to inductive power supplies, or used directly or in ratios for silicon controlled rectifiers or saturated iron core reactors.

1. Switch control method. Many single-point induction heating applications, such as preheating and heat treatment, are designed to first heat to a certain temperature before further heating. The requirements for temperature sensing devices and controllers include: accurate display of workpiece temperature, minimum temperature adjustment, and generation of signals to start work after heating. For this application, a temperature sensing device and a double-click switch controller are sufficient. As its name suggests, the switch control method can be called all or nothing heating energy. When heating, the energy is always kept sufficient until a predetermined or given temperature is reached, and then the energy is turned off. The heating timer and appropriate relay allow a given temperature to be maintained for a certain period of time.

2. Proportional control method. Many progressive heating applications require maintaining a temperature for a long time. These include the quenching and tempering of steel plates and the annealing of wires. These tasks are completed by induction scanning methods. The growth of single crystal silicon is another application that requires strict temperature control, requiring very precise temperature maintenance to slowly extract the seed crystal from the solution. In these cases, another method called proportional control is often used.

Proportional control uses three operating quantities. These quantities are used to reduce temperature fluctuations. The function of the proportional column is to control the output air cooling control operation control generator signal. It is a proportional amount that is adjusted by adding the ratio of the workpiece temperature to the predetermined temperature value. In addition to the control amount, the proportional amount functions very much like a Switch controller. When the temperature reaches a predetermined temperature, the controller will reduce the input power of the coil to prevent overheating or underheating.

However, the proportional motion quantity itself cannot measure the heat required to maintain the temperature. Therefore, the temperature drop tends to oscillate. In order to stabilize the controller at the required temperature, each control quantity in the chain of speed and reset should be used. Speed refers to the speed of the predetermined temperature change of the workpiece temperature. A large change in the workpiece temperature will cause a large change in the control signal, and the amount of change is larger than just using a proportional amount. The reset function is to consider the time difference between the workpiece temperature and the set value. The longer the time, the greater the temperature difference.