Introduction vacuum heat treatment is applied to manufacturing industry, in order to make the industrial products with good performance among the necessary working procedure, it is a branch of heat treatment, the main purpose is to prevent the workpiece oxidation and decarburization in the machining process.
Due to the application of programmable controller the microelectronics technology and computer technology, all kinds of control functions are implemented by software
, as long as change the program, can adapt to the change of the production process, and strong adaptability.
Thus can switch quantity control, analog control, also can got behind with the computer network, to realize hierarchical control.
PLC and small volume, light weight, compact structure, short development cycle, installation and maintenance workload is small.
Therefore, in the process of to transform traditional industries with microelectronics technology, the traditional relay control system, most of the replaced by PLC.
In this paper, it is through combining PLC and vacuum heat treatment furnace control system design, put forward the overall train of thought, and has carried on the system hardware and software design.
Working principle of the control system of 1 first of all, will be scheduled to work on the PLC
and controlled vacuum heat treatment of electricity, and ready to send signals to the industrial control machine.
Since then, the use of industrial control machine start control operation of the whole system.
Work process, the PLC on the one hand and the data communication between industrial control computer, on the one hand, control the normal operation of the vacuum heat treatment furnace.
When PLC receives the data extraction from the industrial control machine after the command, the collection situation of the vacuum heat treatment furnace, such as state of the vacuum degree in the furnace, the temperature, cooling water, and parts of switch state data is sent to the industrial control machine, such as when data is sent, PLC and continues to control the vacuum heat treatment furnace.
PLC to control the equipment mainly by contactor, solid-state relay and other electrical components of peripheral circuit to control the pressure valve, vacuum pump, the operation of the resistance wire and other components, gas operation, to limit and fault alarm.
And industrial control machine on the one hand, the received data processing and display, on the other hand, waiting for the arrival of the second clock interrupt signal, ready to send a command to extract data and receive from the data.
Control system is designed for a industrial control machine to connect two PLC, will extract each PLC data regularly, reciprocating PLC to control two work by turns.
2 control system of general layout equipment with PLC controller
as control core, industrial control computer as the monitoring and display.
Using thermocouple return temperature signal, through the comparison with the set value output controllable pulse to the solid state relay to control the temperature.
Return to vacuum using vacuum sensor signal, and then according to the vacuum values into the next phase of work, and drive the electromagnetic valve and vacuum furnace to achieve the required vacuum degree.
For circulating water sensor monitoring, when an alarm condition is processed in a timely manner.
By controlling the circulating water valve and circulating water pump open coordination of the whole factory all vacuum furnace water consumption.
Through PLC program control oven door line switches and rotary switches.
General layout diagram as shown in figure 1.
3 control system design control system consists of power supply
system, vacuum control system, the heating control system, the oven door switch cars in and out of the control system, circulating water control system.
The power supply system for manual operation.
In vacuum control system, for example introduces system design scheme.
Steps is to use PLC programming, by the mechanical pump, rhodes and intermediate vacuum pump, diffusion pump.
Take to reach a certain vacuum degree and the diffusion pump prepared a long time to open the diffusion pump, concrete principle as shown in figure 2.
2 system hardware design of PLC control system hardware is made up of PLC, input/output circuit and peripheral equipment, etc.
System according to the size of vacuum heat treatment process needs, vacuum heat treatment furnace of PLC sequence control system hardware is shown in figure 3.
because of the vacuum heat treatment furnace with closed loop control and PID control, communications, networking, etc. , so the control circuit is relatively complex, so the selection of large and medium-sized PLC can meet the requirements.
Because of this control system control object is a volume of 10 cubic meters of vacuum heat treatment furnace, adopting PLC type of S7 - is determined
300, vacuumizing system of external components even meet in figure 4.
Including NL1 -
BW1 VP13 for pneumatic valves -
BW5 for pump body cooler, PT1 -
PA3 for vacuum sensor, PD1 -
PD3 for pressure gauge.
By the mechanical pump NL1, NL2, NL3 primary vacuum, NZ1 intermediate vacuum, ND1, ND2 high vacuum.
3 PLC control system software design step
Making vacuum furnace operation plan.
According to the requirements of heat treatment process, the analysis of the thermocouple, and control input parameters, such as vacuum contactor and solid state relay output signal and the logical relationship between various operations, to determine the amount of need to detect and control method.
And design of each equipment in the vacuum furnace system operating content and operating sequence.
Can draw a flow chart accordingly.
Draw flow chart of vacuum and temperature control.
Set of PLC control system anti-interference measures, such as power supply isolation, peripheral circuit of photoelectric coupling.
Program, according to the input of the object as a thermocouple and the output signal as control pulse of the solid state relay and the selected model of PLC, allocate hardware resources, for the various relay ladder diagram or contact number, then according to the technical specifications, using ladder diagram programming.
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