Salt furnace temperature-controlled cabinet design and implementation of

　　

Introduction

Surface treatment is machined, instruments and meters manufacture, electronics manufacturing and other industries in a very important aspect, it not only makes the production of products for beautiful, beautiful, and, more importantly, can be played on the products of corrosion, rust, corrosion-proof and protection.

So the surface treatment of the good and the bad, the direct impact on product reliability and service life. I plant for the surface treatment of salt furnace is the product in the early 1980s, can only rely on manual control, and the temperature display is not intuitive, control the process slow, produced product quality does not meet current requirements. Manufacture of salt furnace temperature control cabinet for salt furnace Automation control, so that old products through innovation to achieve the advanced level of the current industry, is the salt furnace control cabinet design total goals and requirements.

Technical performance and requirements

Control salt furnace tempering furnace and heating.

Transformer-contact fixed, in the furnace used in the process of increasing the current methods of control of furnace. Design, measurement, temperature range: 400 ¡æ _1200 ℃; temperature control accuracy: 5 ° c; measurement error: 3 ° c; thermocouple: Nickel-chromium-nickel-aluminum (SI) thermocouple; power: 3 phase 380V/, 165KW (per phase current 250A). Have set the temperature and measuring temperature display function, with operating voltage and current display. The digital display setting temperature and measuring temperature, voltmeter and ammeter displays operating voltage and current. Have emergency power failure, leakage protection, over-current protection, and other security measures.

The overall design and systems

　　

　　

Figure 1 salt furnace temperature-controlled Cabinet principle block diagram

Salt furnace temperature-controlled Cabinet principle block diagram shown in Figure 1, includes the following sections:

1. temperature control: temperature control by temperature regulator (temperature measurement and control circuits), salt furnace temperature signal by thermocouple input to a temperature regulator, temperature regulator on the input of the sample temperature signal and analog-digital conversion, display measurement results and comparison with the set temperature, temperature control signal output.

2. furnace control part: potentiometer, adjust the potentiometer change furnace manual voltage control pulse generation time, thereby controlling the solid state relay on, to achieve control of furnace current purposes.

3. pulse generation and delay circuit parts: transformers, rectifiers, operational amplifier, timer, circuit, generation and synchronization of 50Hz AC trigger signal, control of on-solid state relay.

Trigger signal generation time affected by temperature regulator and furnace signal control.

4. master parts: including control buttons, air switch, electromagnetic relays, solid state relays, fuses, displays current and voltage transformer and which control button has started, emergency power-off function, fuse to over-current protection, etc.

Specific circuit design

Temperature measurement and control circuits

Temperature measurement and control circuit diagram as shown in Figure 2, it is mainly composed of thermocouples, magnification adjustment, A/D conversion and connector, 8031 single-chip system and drive circuit.

Its work is, according to surface treatment on salt furnace temperature requirements through the keyboard on the control of the process for setting, the MCU first six Nickel-chromium-nickel aluminum thermocouples on the furnace temperature to be detected, and the data to detect for the appropriate handling, last MCU based on test results and design values of the margin size output control signal, the signal output via driver circuit, gave solid state relay control circuits, as well as through the relay circuit control salt furnace heating voltage and current size and time to salt furnace temperature control.

　　

　　

　　

Fig. 2 temperature measurement and control circuit block diagram

Solid state relay control circuits

Solid state relay control circuits, as shown in Figure 3, mainly by check zero circuit, sawtooth formation circuit and pulse forming circuit.

Solid state relay control circuits of a temperature regulator output signal or furnace manual signal is converted into control pulse, by three-phase alternating current solid state relay for control of breakover time, complete the input power of control. Its work is checked zero circuit on 50Hz, 220V power phase for testing, production and power phase of Sawtooth wave, sawtooth wave in sync pulse forming circuit and from the temperature control instrument to compare the DC signal, when sawtooth voltage is less than DC control voltage, sync pulse forming circuit output is pulse, the solid state relay breakover, power supply power to the load.

　　

　　

　　

Figure 3 solid state relay control module block diagram

DC control voltage to control synchronization pulse width, the width is large, thereby breakover time long control added to the salt furnace input power.

Other circuits

Other circuits mainly by current switch, contactor, the digital display working status indicator circuit, etc.

Software design

* Enter the parameters: temperature, insulation temperature ¢ alarm temperature, holding time.

* Auto-record the start time of the insulation temperature and holding time at the end of the alarm signal.

* Completion of data collection (should be at the complete multiple object data acquisition), and based on the collected data for display, and output control signal of the corresponding object.

* When the task finishes, you can print out the measurement of temperature and corresponding time (every 5 minutes and save time) that represents the relationship between temperature and time.

Software process as shown in Figure 4.

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Figure 4 software flowchart

Conclusion

Salt furnace temperature-controlled Cabinet developed and used to make the original salt furnace increase automatic control functions, and simple operation, high reliability.

Currently, this product has been applied to different Workshop 3 salt furnace, the product has reached the design specification requirements.

Reference documents:

1. Zhang is Mian, etc, the automatic detection, press

2. Liu Huibin etc, the measurement technology, Beijing Aerospace University Press

3. Wang Kwong hung, the automatic control system design, aerospace press

4. the MCS-51, principle and application of 96, Beihang University Publishing House

5. let Lee, measurement and control of the computer, Beihang University Publishing House