How to use PLC to control the heating furnace to realize free adjustment -

1, the introduction

electrical heating control is very common in industrial control project. Heating control in temperature control for see, in addition, some equipment need adjust heater power to meet the process requirements. The output power of the heater and current and the resistance of the heater itself through its two ends. In many applications, the heater power regulation, adjust the power supply voltage is used to realize common transformer method is easy to control, but increased the cost of inputs, not convenient automatic control, and in large amounts of heater power need adjust alone cannot be completed. Also used in running through to adjust the power to change the electrical resistance of the heater this way is difficult to implement in hardware.

2, hot bending furnace heating control requirements

in auto glass deep processing equipment, glass hot bending furnace heating control is the typical case of the heater power regulation control. To make flat glass bending furnace heating bent into a spherical automobile front glass, according to the different needs of the heating power is usually around the glass to a tuning a few bigger, heater power rating of 60% Around 100%, in order to make glass curved radian; And the glass in the middle of the heating power are usually get smaller, heater power rating of 0% 65%, smooth curve radian transition in the middle of the glass.

without using under the condition of transformer and other equipment, through experiment, the writer summed up the transistor output through solid state relay control heater based on PLC, conduction time, from the ground to adjust the output power of the heater new effective attempt. In fact, this way not only save the cost, and easy to control. The following theoretical analysis how to realize the use of PLC controller to control the freedom to adjust the heating power.

3, the control principle of

to illustrate its control principle, we first from the alternating current (ac). A cycle average cycle of zero current ( Or voltage) Is called alternating current ( Or voltage) , changing with time according to the sine law of sinusoidal alternating current. And most countries in the world in our country, the electric power industry standard frequency, the so-called '' power frequency 50 hz. According to the electric frequency sine formula f = 1 / t, shows that its cycle is zero. 02 s, its angular frequency for omega = 2 PI f = 100 PI, namely the power frequency sinusoidal 100 times a second to reach zero value ( Sinusoidal instantaneous value twice in one cycle is zero, the regulation between the instantaneous value from negative to positive change a value called the heap) 。 That is to say, in a 1 second of time, every increase 1 phase PI rad ( Radians) Half a cycle, sinusoidal, accounted for 1% of the whole 1 second time phase Angle. Can take 1 seconds time to experience this cycle is divided into 100 equal pieces, 1 per half cycle. So, if we can have a kind of controller, as a cycle to 1 second, in the 1 second time make the heater conduction only 0. 01 seconds, then its power output is 1% of the rated power of the heater; If within 1 second time make the heater only conduction 0. 02 seconds, then its output power will account for 2% of the whole heater power rating, and so on. Thus, through the conduction time control of the heater, can achieve the goal of the heater power regulation. This kind of controller can be realized by PLC controller high-speed transistor output. PLC transistor output unit through the output pulse cycle for 1 second, change the pulse state of 1 time, to control the conduction of the solid state relay time, the heater power to achieve PLC adjust freely. Figure 1

configuration 'online' operation interface

4, the control program of hot bending furnace heating is divided into several segments, and a certain period of heating wire distribution as shown in figure 1 configuration shown in 'online' operation interface. Figure of each article rectangle represents a fever wire, b1 ( bend1) The number of period of heat wire more than 120. Rectangular bar in the middle of the digital setting percentage for the power, the color of the rectangular bar and setting corresponding as a percentage of the power of the more incline to 100% when the closer it gets to the red color, so that the operator can visually check the overall distribution of the power setting.

in order to make configuration set can be realized, the heating power of the interface must be compiled for PLC control program accordingly. Here, we use mitsubishi q series PLC controller as the main controller, for example, to illustrate the control process of PLC.

figure 2 PLC control program diagram

, sm409 is 0. 01 seconds the clock, d4995 processing, the pulse of sm409 add 1 count when d4995 additive to the figures for 100, just for a second time, the qing 0 when d4995 is greater than 100; D6000 for heater 1 power set point, if the value is greater than the current d4995 numerical, and the power value greater than 0, y360 ( Heater 1) The output is 1, otherwise the output is zero. For example when d6000 value of 30 ( 30% of the rated power) is set to a heater D4995 to 0. 01 seconds incrementing count, when d4995 count value between 0 and 30, due to the number is greater than or equal to 30 in d6000 d4995 current value, y360 output status to 1; When d4995 count between 31-100, due to the value is less than 30 in d6000 d4995 numerical, y360 output state of 0. D6000 value range of 0-100 integer, by adjusting the value of d6000, can the heater 1 output power can be adjusted freely.

5, the complimentary heater power regulation with PLC control, has the advantages of simple circuit, convenient control, especially suitable for the occasion of a lot of heater, power regulation, and easy to realize automation control. The heater power regulation control in industrial equipment to provide reference.

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