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2016 International Conference on Artificial Intelligence and Computer Science (AICS 2016) ISBN: 978-1-60595-411-0 Measurement and Calibrate for Analog Quantity Based on the Control of Mobile Frequency Convertor Bo SUN, Wei-sheng GUO and Gang CHEN* School of Automation and Electrical Engineering, Shenyang Ligong University, Shenyang, China 110159 Email: [email protected] *Corresponding author Keywords: Mobile frequency convertor, Embedded system, Distributed control system, Analog quantity measure. Abstract. There were too many required measurement analog quantities in the control system of mobile frequency convertor, design the extended circuit of multi-channel analog quantity measurement can complete the job accurately and promptly to this problem. Use remote-calibrate method, written analog quantity measure program of the embedded system, accomplish the measurement job of multiple channel analog quantity. The process of calibrate was fast, simple and preciseness, it can be applied to calibrate and check of measure analog quantity in the industry field. It’s easy to master for the relative engineering and technical personnel. Introduction In order to improve productivity, quality and reduce the manufacture costs, it is a general request to realize automation and intelligent of electrical equipment in the production of modern industry [1, 2]. The electrical devices typically select embedded and distributed control system design scheme to solve the complex control problems of industry field [3, 4]. The embedded analog measurement technology was one of core skills of distributed control system [5, 6, 7]. Measurement Circuit of Analog Quantity of the Control System Control system of mobile frequency convertor was a power generation and distributed system, which can provide power for the field electrical device. According to the consumption of load, control four motors electricity supply alone or parallel operation output electricity to the load. The system need to measure the voltage and current exactly, control the relays automatic switching, realize overload protection so as to guarantee the mobile frequency convertor operation normally and power supply safely. The required measurement analog quantities in the field were voltage signal, its range from 0v to 5v, select the MPU (Micro Processing Unit) XC2365 as the control core, configure peripheral circuit consist of the control terminal, form the control system of mobile frequency convertor finally. Due to control terminal need to measure 24 channels analog signals, the 10bit A/D converter of the microprocessor less than it, only have 15 channels, in order to ensure the precision, decrease the development costs, the researchers design multi-channel measurement circuits of the analog. The Control System Structure of Mobile Frequency Convertor The frame of embedded distributed control system as shown in fig. 1, it was composed of a main control board, a main control panel, two slave control boards and two slave control panels through MAX487 connect each other form the control system network. The control boards complete the control and measure function of switch value, the function of analog quantity measurement with actuators. The main control board can measure 8 analog channels at the same time; the two slave 516 control boards need to extra design multi-channel analog detect circuit measure 24 channels analog quantities respectively. The slave boards specially designed the multi-channel circuit for measure. In Fig. 1, the supervision computer connect each microcontroller with MAX487 too, use dotted line substitute the field-bus in the picture, if the connected control panel or board was free, the dotted line can be removed. The distributed control system was able to realize remote calibrate to the analog detect which came from the control boards; monitor the states of whole input and output switch value, the measure value of analog quantity. Besides, this system also can test the quality of circuit boards in the operation process of the control system; monitor the mobile frequency convertor online. Figure 1. Control system frame. The Single Circuit of Measure Analog Quantity One of the analog quantity measure circuits was shown in Fig. 2, it was composed of resistant R1, R2, R3, and two voltage followers. In this section, capacitor C1 and C2 filter the interference signal, diode D as the protection element to ensure the voltage didn’t over range. The relationship between output voltage Vo and the input VI as follows equation (1). VO R3 VI R1 +R2 R3 (1) The relationship between protect voltage VD and input voltage VI was shown in equation (2). VD R2 R3 VI R1 +R2 R3 (2) 517 Figure 2. The single measure circuits of analog quantity. Assign the three resistant R1, R2, R3 different value; keep the value of Vo in the linear area of operational amplifier composed of the voltage follower when the input voltage below 5v, made Vo according to the linear change of VI .The light emitting diode breakdown when VD is higher than 5v. Consequently, the amplitude of Vo was limited under 5v, guarantee the microprocessor operation normally. The Extended Multi-channel Circuit of Measure Analog Quantity Due to the required measurement analog of the slave controller was too much, select the analog switch chip HC4051 to finish the detect job, form the multi-channel extended circuit, as follow in figure. 2. Use three switch value output terminals of MPU to drive the high-speed latch HC373, according to the built-in address selection interface A, B and C equate different values to choose the analog channel, transfer the signal to the A/D module which attach to the single chip finish the 8 channels analog quantities convert to digital signal in chronological order. The relationship between values of pin A, B, C and selected channel was shown in Tab. 1. Design the extended circuit measure 24 channels analog signals just need MPU XC2365’s three A/D pins, the rest were used for switch value input terminals. Table 1. the relationship between A, B, C and selected channel. The address select pin of HC4051 A B C INH 0 0 0 0 0 1 0 0 The selected channel X0 X1 0 0 1 1 1 1 1 1 0 0 1 1 0 1 0 1 0 1 0 0 0 0 0 0 X2 X3 X4 X5 X6 X7 It takes some time for the channel shift of chip HC4051, other hardware circuit operation also generate time delay, when the microprocessor send instruction to the latch HC373 select channel, the timer of single chip will delay few microseconds, wait for the voltage of selected analog channel 518 became stable, then begin A/D conversion, the delay time of the control system of mobile frequency convertor was 10ms. The Calibrate Method of Measure Analog Quantity Calibrate was method that develop relevant norm to transform the pending measured quantity into digital quantity; the output signal was easy to process by MPU. The process of calibration just like a ruler, researchers uses it to detect the analog. Method of Two-point Calibrate As in figure 2 and equation (1) shows, Vo and VI satisfying the linear relationship. Base on this, VI with the A/D conversion value Lzy of Vo also satisfy the linear relationship too. Their linear relationship can be inferred on the basis of Law that two points determine a line, then formulate measure standard and detect the analog. Figure 3. The linear relation diagram of A/D. The linear relationship diagram between VI and Lzy as shown in Fig. 3. When VI take different values Uzmax and Uzmin, the relevant A/D conversion value Lzy of MPU XC2365 equate logic full value Lzmax and logic zero value Lzmin .The relational expression as equation (3). When VI U z max , then Lzy Lz max (3) When VI U z min , then Lzy Lz min Download the program which write by C language to the MPU, send the value of Lzmax and Lzmin to the calibrate array of Flash for storage, it reminds worker the calibrate process of current analog quantity measure was over. Measure Analog Quantity In the initialization process of microprocessor, if logic full value Lzmax and logic zero value Lzmin was read out from the calibrate array, the next step detect the analog was begin, transfer the input voltage VI to the relevant logic value Lzy , define the logic slope as the follow equation (4). KL Lzy Lz min (4) Lz max Lz min The measure value Uzy of analog quantity VI was calculated by equation (5) as follows. U zy K L (U z max U z min ) U z min (5) 519 The calculate equation of relative error δ between measure value Uzy and the required analog VI as follows equation (6). U zy VI VI 100% (6) The Remote Calibrate of Measurement Analog Quantity Remote calibrate was a method that the monitoring computer exchange information with the control terminal, issuing the instruction of calibration to microprocessor, and achieve it by particular slave control board. The monitoring computer serial communication with the main control board and the slave control board under the control of computer program, the format of data frame was shown in table 2. In order to avoid wrong actions, the analog quantity realize remote calibrate need three rigorous requirements. 1) Connect reference voltage Uzmax or Uzmin at the input of the measurement analog circuit, Uzmax match the calibrate of logic full value Lzmax, and Uzmin correspond to the calibrate of logic zero value Lzmin . 2) The calibrate demand was sent by the main control board or the slave control board, if the specific digital input terminal which link the pull-up resistors was pushed down to low level. The measurement analog in this paper select the method above. 3) When the monitoring computer send out data to the control boards in the format of Tab. 2, point out the logic full value calibrate or the logic zero value at the same time. Table 2. The format of data frame. Header 5bytes Direction 1byte Instruction 2bytes Check 1byte The main control board and slave board realize two-points calibrate of the analog and answer the monitoring computer when the above conditions were satisfied. The Experiment of Measure Analog Quantity of the Mobile Frequency Convertor Researcher design a upper computer software on the monitoring computer with visual basic language, communicate with the each control box. Supervise and control the system, achieve the remote calibrate of measurement analog quantity. When calibration begins, set the reference voltage Uzmax and Uzmin equate 5v and 2.5v respectively, use the method in this paper, if the precision of A/D conversion was 10bit, the relative error of main control board should below 0.4%, the slave below 0.5%. Conclusions Study and summarize the remote calibrate of measurement analog quantity via design the embedded and distributed system of the mobile frequency convertor, the conclusions as follows. 1) Use the extended circuit of multi-channel measure analog quantity can save the microprocessor resources, cut down the design cost of control system. Obtain better detect precision of analog quantity, if the program wrote more reasonable after practice. 2) The two-point calibrate emphasize the process of calibration, when the hardware circuit of measure analog quantity was finished, without modification. This method also can apply in other embedded system to measure the analog. 3) The process of remote calibrate was fast, simple and accurate, it can be applied to calibrate and check of measure analog quantity in the industry field. It’s easy to master for the relative engineering and technical personnel, made the equipment maintenance convenient. 520 Reference [1] Robert P. 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