The multi-point temperature measures system design
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Foreword
In industrial production and daily life, the application of the detection system of the multi-point temperature is very extensive, for example the non-mutilative temperature electric in fire control is measured, the overheated trouble of the power equipment foresees that measures, the temperature of the air-conditioning system is measured, the excessive heating of the tool assembly of all kinds of transportation is measured, medical treatment and temperature test of diagnostic facility,etc.. To this situation, a kind of detection system of the temperature much based on AT89C51, digital temperature sensor more DSl8820 of this text design, this system utilizes the total collinear characteristic of DSl8820 form, can set up the sensor network conveniently, thus realize the measurement of the multi-point temperature. This system design is flexible, anti-interference is good, can carry on thermometry in the abominable work environment.
An overall structure
Detection system of the temperature designed. This system is mainly by AT89C51 one chip microcomputer, display circuit of the keyboard, display circuit of temperature, watchdog’s circuit, test circuit of temperature, serial port communication channel,etc. make up. The multi-point temperature of Fig. 1 measures the block diagram of the system hardware Structure chart within Fig. 2 DS18B20
2 hardware circuit
2. Test circuit of a temperature
The test circuit of temperature mainly adopts the temperature chip DSl8820, it is a line type digital temperature sensor that DALLAS Company produces, the temperature measurement range is – 55- +125 , examine the warm definition reachable O. 062 5 , it have micromation, low power consumption, high performance, better easy to buy characteristics such as the microprocessor,etc. antijamming capability, especially suitable to form the multi-point temperature to observe and control the system. Its internal structure.
DSl8820 has 4 master data parts:
(1)64 laser ROM. 64 laser ROM are successively 8 CRCs, 48 sequence numbers and 8 codes (28H) of family from high position to low order Composition;
(2)Temperature sensory element;
(3)Non-volatile temperature alarm flip-flop TH and TL, can pass user’s warning upper and lower limit of the software load;
(4)Dispose the register. Dispose one byte of register in scratch pad memory. DSl8820 converts the temperature to the number value of the corresponding precision according to the definition in this register when 0 works, its every definition. Fig. 3 DS18B20 disposes the register structure
In Fig. 3: TM is the mark bit of the test pattern, the load 0, can’t change when being dispatched from the factory; R0, Rl sets up the location for the thermometer definition, 4 kinds of corresponding definition of it are set out in Table 1, R0 while dispatching from the factory, R1 puts for default value: R0 =1,R1 =1 (namely 12 resolution ratios) ,Users can rewrite and dispose the register in order to obtain appropriate definition depending upon need. Table 1 disposes register structure and definition relation to express
The scratch pad memory is made up of 9 bytes, it assigns. After the temperature changes the order to release, through change resulting the intersection of temperature and value, leave O and one byte of scratch pad memory in in the form of base complement of two bytes. The one-chip computer can read this data through the single line interface, the low order is in the front while reading, after the high position, data format. The correspondent temperature is calculated: Look on as sign bit S =At the O, change binary digit into the decimal system directly; Act as S =At 1 o’clock, turn the base complement into true code first, and then calculate the decimal system value. Fig. 4 DS18B20 register reflects the image pattern
Because DSl8B20 is a digital temperature sensor of single wire, it does not basically need peripheral circuit to link with the one-chip computer with a line directly, Fig. 5 is the schematic diagram that a plurality of DSl8B20 links with one-chip computer through the monobus, in the picture, DSl8B20 adopts the power supply mode of the external source. Fig. 5 DSl8B20 examines the warm circuit
2. 2 keyboards and display circuit
What this system adopted is matrix type keyboard, make up 20 key sets altogether, mainly include 10 numerical keys and ” upgrade ” , ” lower limit ” , ” determination ” Wait for the function key. When it is pushed that there are keys, 8279 produces the interrupt signal to send into the one-chip computer, then turn to the corresponding function procedure.
Reveal that adopts film 75451 to link with 5 LED nixie tubes partly to realize the dynamic display, under the operating condition, are shown the variation of sign, ten’s place, the unit of the temperature value and the last one of radix point of temperature value of temperature value of channel number, temperature right sequentially from the left.
2. 3 power supply circuit
Because the one-chip computer working power is +5 V, and the bottom layer circuit power consumption is very little, adopting 7805 three terminal steady preform can meet the demands. Concrete circuit. Power circuit diagram of Fig. 6
2. Circuit of 4 watchdogs
Consider the work environment of the circuit board of bottom layer is relatively abominable, the chance of the one piece is interfered with by the ambient enviroment, some unpredictable abnormal functioning phenomena of flying, crashing etc. that therefore the procedure appears to run, staff members can not go to the scene to get up to the one-chip computer again either, are originally designed on the electromechanical way of one piece to add watchdog’s circuit of a piece of outside, inquire about the working condition of the one-chip computer regularly, once finding abnormality will delay time and get up to the one-chip computer again promptly, by the operation with safe and reliable security system. Its circuit. Watchdog’s circuit of Fig. 7
3 software design
The systematic software adopts the modularization method to carry on programming, mainly scanned by main program, nixie tube display program, keyboard and key set handler, temperature test procedure, interrupt control routine,etc. make up. Among them the main program finishes system initiation and calculates etc. the temperature that is gathered; Keyboard scanning circuit and the intersection of key set and handler realize the intersection of input and recognition and relevant to punish of key set of keyboard; The test procedure of the temperature mainly finishes being conveyed machine format treatment by the temperature chip, and judge and reveal; The display program of nixie tube finishes sending and counting to the display of the number, the display part of the control system; The interrupt control routine realizes and circulates the display function.
Systematic program flowchart. Systematic program flowchart of Fig. 8
4 concludes the speech
Can realize detection and control of the multi-point temperature with AT89C51 one-chip computer and DSl8B20 digital temperature sensor. Such characteristics as it is strong that the system has digitization of signal, hardware simplifying and antijamming capability, if can the intersection of extended interface and chip link with a corresponding one, can realize multi-channel measurement of temperature and control, in order to meet the need of industrial production.
