Design the guide in proceeding control and PLC
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Summary: Programmable logic controller (PLC) In the process control system can be valid save time, reduce cost and energy consumption, simplify system design. Can know how to substitute the discrete circuit with modern IC from the development process of the manufacturing industry. These IC can simplify system design, expands the apparatus and monitors the function and ensures the security of the operating personnel. MAX15500/MAX15501, MAX5661 and MAX5134- MAX5139 are typical IC in the proceeding control is employed.
Brief introduction
Industrial control, factory automation and PLC (programmable logic controller) Develop mature technology, can save the time, material, energy and money effectively. But how to start Design a totally unattended factory to be an enormous project, give up when not probably starting the project yet.
This makes us remember an explorer of Africa many years ago, as he inquires a local clan man: “How to eat up an elephant ” ,This man sees explorers answer in surprise: ” we eat elephants just as eating anything other, one for once ” . Like other large-scale system development, the industrial control system can be divided into a lot of small-scale circuit. Now we begin to canvass the circuit after these are subdivided.
Control flow chart of the course
The assembling line is quite new invention and creation in the history of mankind, the similar innovative scheme emerges in the same period in a lot of countries. We will enumerate several examples among them, will explain how to perform and enter an intact automatic factory.
Samuel Colt (* manufacturers of U.S.A.) Showed a kind of common part in the middle period of the 19th century. Er early * needs to make the part of each rifle independently, then assemble. Mr. Colt has shown the common parts of 10 rifles, then pick these parts and assemble a rifle well from the case at random. In the initial stage of the 20th century, Henry Ford further expanded the production technology in enormous quantities. He adopts the stationary assembling plant, transports the spare part among factory by the truck. Employees only need to understand little assembly knowledge, only carry on the operation in the work afterwards too. In 1954, George Devol applied for American patent 2,988,237, this patent marks the birth of the first industrial robot, this robot is named as Unimate. The latter stage of the sixties of the 20th century, General Motors Use PLC (the programmable logic controller) Assemble the automatic gearbox of the car. Dick Morley known as father of PLC has produced first PLC for GM. His American patent 3,761,893 is the foundation of a lot of PLC (detailed information about above-mentioned quad bit inventor at present, please consult: www.wikipedia.org/; Please inquire about the relevant patent: http://patft.uspto.gov/netahtml/PTO/srchnum.htm) .
To which kind of extent briefly can proceeding control Fig. 1 provides a common home heater. Fig. 1. The electronic heater of the family expenses, a simple proceeding control example.
The part of the heater is sealed in a container, simplifies system communication. The concept can expand thermostatical heater that control distally to, communication distance in several meter about, usually adopt voltage control.
Now, we can consider a miniature simple process control system, which essential parts are needed in the factory illustrated in Fig. 2 Fig. 2. Telecommunication of the factory
Transmit collinear impedance, EMI and RFI (electromagnetism and radio interference) at a long distance Make the implementation of the control scheme of the voltage very difficult, in this case, the electric current loop can yet be regarded as the simple, valid solution. Knowing by the Kirchhoff’ law, any a little electric current is equal to the sum of a bit all more other electric current in the cycle in the electric current loop, therefore can offset the resistant influence of transmission line. Because the cycle impedance and bandwidth are lower (several hundred ohms, < 100Hz),EMI RFI
PLC basic principle
The cyclic(al) application of current control started in the Er early electric typewriter in the 20th century, it was 0- 60mA cycle that used at first, changed into 0- 20mA cycle later, PLC system took the lead in putting into 4- 20mA cycle. 4- There are a lot of advantages in 20mA electric current loop, regards 4mA as the electric current of lowest communication, the transmission line is disconnected (open a way) When trouble of detecting on this,need two pieces not to be can realize whether sensors distal supply power if wired only, about 3.5mA. 4- 20mA cycle can adopt the analogue communication, can adopt digital communication too.
Need calculation carefully in the traditional discrete device design, and the circuit takes up the larger space. Maxim has introduced several 20mA devices, can simplify system design greatly. We consider the typical PLC function at first. Fig. 3. PLC simplified block diagram
PLC is used for finishing a certain jobs or tasks. We measure a physical parameter first, deal with and carry on decision it, then the order, a certain physical device, carries on movements. According to this model, the left lower frame reveals signals are recuperated and exported, can adopt MAX15500/MAX15501 integrated circuit.
MAX15500/MAX15501 allows to be chosen the voltage control or long-range current control of the short range. Can be found out from Fig. 4, besides basic communication functions possessed in traditional points of cube cases, have joined new monitoring and protection function in the device. Fig. 4. MAX15500/MAX15501 exports recuperating device serial products, the device function includes: 12V provided for 1k loads reaction and exports, supplies 24mA electric current of 750, 100 µ 14 periods of build-up time of s, 40 µ 12 periods of build-up time of s.
The routing of factory is influenced by factors such as the movement, shaking,etc., may cause the open circuit with other interface units or short out. In order to guarantee apparatus and personal security, the need is gone on and monitored safely. When the cable fails, will have the spacing interval of segment before the system fails completely. Series MAX15500 can be monitored intelligently, different invalid states of management.
In view of the factory extreme EMI, RFI, power surging condition, the measure of any control must be reliable, can be free from interruption by external environment. Series MAX15500 include the open circuit of a minimum 260ms, short out for overtime, the mistake enough to avoid monitoring the noisy environment to cause calls the police this time cycle, and catch the transient cabinet fault enough. In addition, the device will latch the trouble and touch off an independent hardware interrupt pin and call the police, thus enable the fast response cable short trouboe of the processor. The register content that can read MAX15500 of the processor of bringing up the rear while receiving, obtain the accurate failure message, remove malfunction interrupt. Besides monitoring the state of the cable, the device offers other safe functions, for example, is it the excessive heating to control the environment through measuring the chip temperature. The adjustable power falls and measures the threshold very crucial to reliable system design, the mains voltage measures the threshold and can be regulated in 10V to 24V range, difference is 2V.
Safe for security system, it also has overcurrent protection, over the ground short circuit protection and is up to the overvoltage protection of 35V that MAX15500/MAX15501 exports. In order to meet customer’s demand, MAX15500/MAX15501 offers programming ultra quantum ability. Some users adopt 105% of the scale span, even 120% are tested or dealt with promptly(the system may be out of the partial fault or strong noisy environment) . MAX15500/MAX15501 adopts 32 pins, 5mm² TQFN capsulates, there are naked pads, improve heat abstraction.
It accords with HART® that MAX15500/MAX15501 exports the recuperating device; The standard, HART (the distal sensor of addressing of high speed) The agreement can bear the weight of the two-way digital signal on 4- 20mA control circuitry, is similar to 1200 baud rate, Bell 202 agreement used for fixing the telephone call.
MAX15500/MAX15501 also has independent SPI&-#; 8482; Bus line, has reduced the required opto-isolator of electrical isolation. What the device is adopted is the interface of special self-timed SPI, support the chrysanthemum chain agreement. When a plurality of SPI devices need controlling through the electrical isolation, this kind of mode contributes to the demand that reduces the control line and isolates the photosensitive resister.
In smaller PCB (PC plate) Have and integrate more multi-functionally
Discrete, available voltage (unipolarity and bipolar) of design Or the Tap regulation circuit is that a pole has task of the challenge, especially as the designer knows that needs to control the variable gain of the scale span, while resetting level, 0mA and 4mA circuit demand to many kinds of the unipolarity and what the bipolar voltage is set up, will be to the complexity of the system and further understanding. Having simplified the function design in Fig. 5, because these functions have already been integrated inside MAX5661 electric current and voltage output DAC. Fig. 5. Simple functional block diagram of MAX5661
MAX5661 has solved the cube dividing case and designed the difficult problem through its function of programming, can choose the following parameter conveniently:
Output voltage
Unipolarity range: 0 to +10.24V, 25%
Bipolar range: 10.24V, 25%
Tap
The low-grade range of the unipolarity: 0 to 20.45mA
The top-grade range of the unipolarity: From 3.97mA to 20.45mA
The scale span outputs the gain to noise temperature ratio
Out-of-range with 10 definition or what the interval is adjusted to and up to 25%
Asynchronous to reset clear, or preset to 16 digits
These functions are offered design flexibility, when as the analog power supply, it is 13.48V to 15.75V to export the voltage range; At the time of Tap, the excursion of output voltage is: From +13.48V to +40V. The voltage output of the differentiating can measure to realize that measures long-rangely through the loading / reaction of the voltage out amplifier. The intersection of trouble and output break point out, open a way Tap, short out voltage output or state drive out. This function is driven by the voltage output of the current limiter; As to Tap, differential pressure detector monitors the Tap of overrunning. /LDAC pin is used for controlling asynchronous DAC to upgrade and many DAC synchronization systems.
The above-mentioned all functions are integrated in MAX5661 10mm x 10mm LQFP capsulate.
Utilize voltage and electric current to recuperate to offer much PLC to export
Obviously, can utilize lamellar MAX5661 16 devices to offer other additional functions, but, can consider other schemes in needing low resolution, low-cost PLC system, Maxim offers the definition as 6 to 16’s DAC, has more than 2500 kinds of different types devices. The passways of this series of products are chosen to include: 1 to 4 passways, 8 passways, 16 passways and 32 passways. The communication interface includes running side by side, high speed SPI and I² C I2C,etc.. In addition, can also choose fast build-up time ‘ < 1µs) (SOT23 QFN µMAX®) (= 1 LSB INL)
The high-accuracy DAC series products that Maxim was put out recently include MAX5134- MAX5137 and MAX5138/MAX5139, these DAC includes six buffer voltage outputs of available No.. All device adopt, supply power from +2.7V to the intersection of +5.25V and the intersection of form and power, offer Line 3 SPI/QSPI&-#; 8482; /MICROWIRE™ /DSP compatible serial interface.
MAX5134- MAX5137 is that a pin is compatible, software compatible 16 and 12 DACs. MAX5134 is 16 devices of four passways, INL is 8. MAX5135 is likewise four passways of DAC, the definition is 12, INL is 1; MAX5136 is 16 devices of double channel, INL is 8; MAX5137 is 12 devices of double channel, INL is 1. It offer being ultra small dimension (4mm² each section DAC) , 24 pins TQFN are capsulated, work and expand the temperature range of technical grade in – 40 degrees C to +105 degrees of C.
It is in MAX5138/MAX5139 for single channel, pin and software is compatible for DAC, it last small dimension (3mm²) , 16 pins TQFN are capsulated. MAX5138 is 16 DACs, INL representative value is 2; MAX5139 is 12 DACs, INL representative value is 0.25.
The high-accuracy basic reference of high-performance MAX5134- MAX5139 built-in 10ppm / degree C, can use the outside basic reference too, in order to support all over excursion output. Utilize one hardware input pin, control output of DAC set up, can output, locate 0 or intermediate value DAC during power up or reset. This characteristic has offered supplementary protection for the fact that it is employed that the valve drove or other needing to be in the inactive state transducer during power up. Hardware load DAC (/LDAC) The pin supports the upgrading synchronously of lamellar DAC. Serial interface offer / export by READY, simplify lamellar MAX5134- MAX5139, MAX15500/MAX15501, the intersection of MAX5661 and the intersection of device and control at the interlinkage.
Export PLC application as to No. 4 of the high cost performance, can choose MAX5135 four passways of 12 DACs and four passways of MAX15500 to export the nursing one’s health device.
Conclusion
High linear scale and outputting and recuperating the function to make these devices used in high accuracy control and instrument ideally of Maxim DAC. Maxim device offers a simple, wise choice to designer, can dispel the complicated, larger design of the discrete circuit to perplex. It means choosing voltage or electric-current driving at will to simplify and design, make the busy engineer can be absorbed in the key part of system design, reduce the waste, offer more valid high accuracy control and and then improve our environment.
