Development of computer automatic temperature cont

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Development of automatic temperature control of horizontal vacuum furnace computer

[Abstract] this paper introduces the application of DCS system composed of intelligent temperature controller with single chip microcomputer as the core and monitoring upper computer in the reconstruction of automatic temperature control of horizontal vacuum furnace, and gives the design principle and implementation method of its software and hardware, as well as the technical difficulties and treatment measures in the reconstruction. It is related to national defense, military industry, transportation, energy, medical health and other aspects

1 preface

k88-iia horizontal vacuum sintering furnace of blade branch of self hardening company is an automatic furnace temperature control system designed by powder metallurgy equipment company of Central South University of technology in 1993. Limited to the technical conditions of the equipment at that time, the host adopts a super small automatic control device composed of 286 compatible microcomputer and a/d and d/a boards developed by the company, without hard disk. Up to now, the system has the following serious defects:

1.1 the service life of the host is too long, and in the aging failure period, faults occur frequently, and floppy drives and color displays cannot be used normally

1.2 because there are no replaceable parts, once the system fails, it cannot be repaired

1.3 there is a serious "Y2k" problem in the system software

1.4 the operation is cumbersome and there is no Chinese prompt. The curve of furnace temperature in each zone should be input repeatedly for many times. Without Chinese prompt, the collaborative operation of printing, control and recording cannot be realized

1.5 the control and alarm functions of several test methods of vacuum impact testing machine have failed

1.6 the system has poor anti-interference ability and often crashes

1.7 the temperature of the second zone of the furnace body is always higher than that of the first and third zones, which cannot be corrected

in order to improve product quality, market competitiveness and strict process management, the original control system must be eliminated as a whole and replaced by a new popular industrial computer with standard configuration software and multi input and output temperature intelligent controller to realize automatic control of furnace temperature that meets the process requirements and heating characteristics

2 system design

2.1 hardware design of control system

according to the process technical requirements and the principles of reliability, economy and simplicity, The control scheme of the system is shown in Figure 1:

2.2 according to the range and polarity of the analog quantity and i/o quantity to be collected by the control system, determine the type selection of the temperature transmitter and the supporting process controller input acquisition mode that schools and enterprises work together to overcome the three difficulties, As follows:

input and output signal definition and range:

2.2.1 analog input: furnace temperature: 0-1600 ℃

temperature measuring element: B-type double platinum rhodium thermocouple

temperature transmitter output: 0-5vdc, There are three ways of vacuum degree:

range: 100-105pa

output signal: 0-5vdc/1k Ω

2.2.2 switching input:

2.2.1 start is to measure an unknown voltage signal button: three belt temperature controllers start and run at the same time power failure recovery button: when the controller is powered off, restart the unfinished program process recovery button: clear the currently running process curve, and the program returns to the initial non operational state cooling water flow detection switch:

if the cooling water detection switch is in the "off" state, the computer will give an alarm message, pause the execution of the program, and turn off the output completely. After the fault treatment is completed, press "power failure recovery" again to continue the unfinished procedure

2.2.3 switching value output: electric bell: 1 circuit, 220VAC; Relay control furnace temperature alarm signal lamp: 1-way, red, 24VDC automatic status indicator: 1 circuit, 24VDC manual status indicator: 1 circuit, 24VDC vacuum upper limit alarm indicator: 1 circuit, 24VDC process recovery indicator: 1 circuit, 24VDC insulation indicator light: 1 circuit, 24VDC water shortage alarm indicator: 1 circuit, 24VDC

2.2.4 analog output:

3 channels in total: 0-10madc

external input signal output to zk-200 thyristor voltage regulator for zero crossing trigger

2.3 the principle block diagram of the temperature process controller designed according to the above requirements is shown in Figure 2:

2.4 upper computer software design

the management software of the vacuum sintering furnace computer control system runs on the pwindows9x platform, and the operation interface is intuitive, friendly and convenient. The management and operation of the vacuum sintering furnace controller can be completed with a click of the mouse

the upper computer software mainly realizes the following functions:

2.4.1 real time display the working condition parameter table and operation curve of each vacuum furnace controller, and the operation status of each vacuum furnace controller is clear at a glance

2.4.2 monitor the operating parameters of each vacuum furnace in real time. When the parameters are abnormal, it will automatically switch to the alarm screen. The historical alarm record is saved on the computer for subsequent inquiry and printing

2.4.3 provide the function of querying and printing historical operation curve

2.4.4 real time bar chart and flow chart visually display the current operating parameters of the vacuum furnace

2.4.5 read and modify the operation curve of the vacuum furnace controller. The process curve can be saved in the computer, eliminating the cumbersome input in the future

2.4.6 read and modify operating parameters such as valve opening of vacuum furnace

2.4.7 authority management provides two pole password protection function to prevent irrelevant personnel from using related functions

2.4.8 the software provides database maintenance function

the upper computer software flow chart is shown in Figure 3:

2.5 temperature controller software design

the temperature controller software adopts 8031 single chip microcomputer macro assembly language programming, calls standard PID modules and various functional modules

its software control flow chart is shown in Figure 4

3 technical difficulties and solutions

3.1 the lead of the thermocouple of the original system adopts unshielded cable. In this reconstruction, the original cable is still used at first. However, in actual use, it was found that the detected temperature signal always drifted and fluctuated greatly, and the reason was not found at the beginning, thinking that it was because the modular temperature transmitter was unstable and had poor anti-interference ability. However, it was later found that it was added to the thermocouple after checking the thermocouple input end of the modular temperature change with fluke 192 digital oscilloscope

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