Luoyang Judian Metal Hot Processing Equipment Co., LTD is mainly engaged in the manufacture of complete sets of equipment in the metal thermal processing industry and the integration of the entire production line.
In industrial furnaces, to produce high-quality products, several physical and chemical quantities must remain essentially constant or operate according to a predetermined program. These quantities include temperature, pressure, gas composition, and indirectly, flow rate. The principles of automatic control apply to all of these quantities. Therefore, it is best to briefly discuss these principles before discussing the control of each individual quantity.
The quantity to be controlled (such as temperature or pressure) is called the controlled variable. The variable that itself changes and can change the controlled variable is called the independent variable. In some processes, there are several independent variables.
industrial furnaces
Automatic control is achieved by inducing a force (directly or indirectly) from the controlled variable. This force is balanced by gravity, mechanical spring force, or a corresponding force generated by gas or electromagnetism. The element that generates the balancing force can take many different forms. If the value of the independent variable changes, the value of the controlled variable also changes, disrupting the balance between the induced force and the opposing force. A slight difference between the two forces triggers a mechanism to operate, attempting to return the controlled variable to its original value, called the "setpoint" or "control point."
shows a very simple control system. The water level in a water (or other liquid) tank is the controlled variable. At the setpoint, the upward force exerted by the water on the float exactly balances the weight of the float. At the setpoint, the inflow and outflow of water are equal. If the drain valve (the independent variable) is opened wider, the water level drops below the setpoint, reducing the upward force exerted on the float. The float drops, increasing the inflow of water until the water level rises to a value close to the setpoint. The two drain valves constitute the two independent variables.
The setpoint is usually adjustable, allowing the controlled variable to be changed as needed. In Figure 96, the water level is adjusted by bending the float stem or changing the length of the connecting rod between the float stem and the valve stem.
