Abstract: Take TMS320VC33 DSP as the core, uses the pincer-like current transformer input and the voltage direct input, designed the voltage, the electric current, the power, the mains frequency, the electrical network power factor metering circuit, with power frequency electric quantity reflectoscope reflector which should design in practical application, the effect was good.
Key word: DSP electric quantity reflectoscope reflector Hardware design
One. Introduction
The modern enterprise uses electricity in the system, each kind of instruments and meters are obtaining more and more applications, but take the monolithic integrated circuit as the essence measuring appliance as a result of the speed and the precision question, has not been able to satisfy the people to a great extent to the information processing demand. The DSP software programming is flexible, the degree-of-freedom is big, the true-time operation speed, data-handling capacity goes far beyond the monolithic integrated circuit. This article take TMS320VC33 DSP as a core, designs one kind of processing speed and the accuracy high power frequency electric quantity reflectoscope reflector, satisfies people’s actual need.
Two. Circuit design
1. voltage sample followed electric circuit: Figure 1 is the electric circuit schematic diagram, for the system 0~400V voltage transforms to use in measuring
Figure 1. Voltage sampling circuit
Figure 2. Electric current sampling circuit
the 0~5V voltage signal, needs in the return route the shunt resistance. In order to increase the precision, takes winds through the resistance the electric current is 1mA, and the resistance temperature should be very small, therefore selects the precision big resistance. In order to guarantee that the differential pressure signal between 0~5V, chooses differential pressure resistance number R6=315K, R7=5K.
2. Electric current sample followed electric circuit: Figure 2 is its electric circuit schematic diagram, for the system 0~5A electric current transforms to use in the 0~10mA electric current which surveys, may realize the electric current signal transformation using the transformer, when the measuring signal is 5A, the primary side and the vice-coil proportion are 1:500. Component’s input is a voltage generally, must therefore transform the electric current signal as the voltage signal, only need in electric current output termination one 500 ohm resistance be possible the 10mA electric current transformation to be 5 volts voltages.
3. AD switching circuit: Uses AD73360 a/D switch, AD73360 is 6 channel analog input 16 serial bit programmable A/D switch which AD Corporation promotes. Because uses ∑-A/D the transformation principle, has the good anti-aliasing performance, front end therefore to simulates filter’s request not to be high, it can guarantee at the same time 6 group simulated signals the sampling, and retards in the conversion process is very small. This design uses the d-c coupling the single end input, Figure 3 is and the DSP circuit diagram.
Figure 3 AD and VC33 connection diagram
4. doubling circuit: In order to start a/D switch and measurement system’s frequency, in the system must have the doubling circuit. The sampling circuit sampling obtains sine wave after the OP-07 comparator turned the square-wave, in its one cycle only then two pulses, transform with this pulse enable A/D cannot meet system’s requirements far. Doubling circuit’s function is turns the square-wave more pulses, profile transformation like chart 4.
Figure 4 doubling circuit’s profile transformation chart
CC4046 in doubling circuit’s function is the frequency synthesis. Realizes frequency synthesis schematic diagram as shown in Figure using PLL 5.
Figure 5 realizes the frequency synthesis schematic diagram using PLL
If crystal birth’s frequency is fs, divides M after the fixed frequency dividing circuit obtains reference frequency fr, by fr=fs/M, is delivered on a phase comparator’s input end to do the comparison datum, produces frequency f0 after VCO is divided by a programmable frequency divider N to deliver on phase comparator’s another input end to carry on with fr the comparison, when after locking, then has: fs/M=f0/N Namely f0=N/M fs. In this design, M=1, N=360, fs is after the OP-07 comparison produces pulse frequency. The procedure frequency multiplier is composed of CC4046, it has 360 frequency divisions. After the frequency division signal enters 8253 counters, calculates the frequency based on the counter.
5 analog switch electric circuit: In measured when voltage and electric current, the frequency multiplier must distinguish and the corresponding voltage sampling circuit and the electric current sampling circuit is connected, needs an analog switch to carry on the choice, selects the analog switch is CMOS CC4053. The CMOS multi-channel analog switch electric circuit is composed of the address decoder and the multi-channel bidirectional analog switches, may through the exterior address input, after the electric circuit internal address decoder decoding, the connection and the address correspond a switch. It permits from the n line to 1 transmission or 1 to the n line signal separation, as well as permission signal and - string transformation. CC4053 is three group of two group analog switches.
6.CC4046 and 8253 connections: CC4046 when uses as the doubling circuit, its output signal frequency for its input signal frequency’s N time, the doubling circuit by the phase-locked loop and N enters the system counter to be composed, the counter inserts between the VCO output and the comparator. Thus, when the phase-lock ring lock fixed time, the counter output signal frequency and the phase-locked loop input signal frequency is equal, thus (i.e. the VCO output) obtains the frequency multiplication output signal in the counter clock input end. It with 8253 connection diagram as shown in Figure 6.
Figure 6 4046 and 8253 connection diagrams
7. serial port correspondence realization: In order to expand measuring appliance’s function, enables the measuring appliance to facilitate carries on the data exchange with the superior machine, designed a RS-232 standard serial interface for the measuring appliance, TMS320VC33 has not received the transmission data the function, therefore 8251 took VC33 a serial channel. Because the RS-232 level and the TTL level are incompatible, therefore needs to add MAX232E to take the level switch electric circuit. 8251A takes the programmable correspondence connection component and VC33 constitution serial as shown in Figure 7.
Figure 7 8251 and VC33 constitution serial interface chart
The figure shows: 8251A, the RESET equisignal and the VC33 phase looks carefully the company, 8251A D7~D0 and VC33 low 8 bit data main line D7~D0 is connected. 8251A selects patches or strips of land as worth saving for seed the signal to provide by address decoding electric circuit 74LS138 Y5, is connected with address bus’s A0, uses in the selecting data mouth and the control mouth. After the VC33 clock passes through 8253 frequency divisions, delivers 8251A and the end, takes the 8251A receive clock and the transmission clock.
8. Voltage transformation circuit design: As a result of 8251 TXD and RXD signals and PC machine serial port voltage not symbol, therefore added voltage switch MAX232 between this. Its connection diagram like chart 8. Its interior mainly changes to by one 5V the 10V electricity
Figure 8 MAX232 and RS-232 connection diagram
Presses the multiplier, changes 10V to - the 10V voltage changer as well as two transmitters and two receiver composition. When use only need in exterior connect 4 electric capacities, through the internal double sufficient electric pump voltage changer, may realize pressure-rise and the voltage polarity inversion, transforms 5V ±12V, by takes driver’s power source. Has realized TTL and the EIA232C level transformation not only through this kind of chip, moreover may simultaneously complete between positive and negative logical the transformation, uses is convenient.
9. the memory expands: Am29LV800B is a 8M position, 3.3V dodges the fast memory, this memory has the 1M byte or the 512K16 bit word. 16 bit word data appear on DQ15-DQ0; The byte wide data appears on DQ7-DQ0. This component only needs the single 3.3V power source to be possible to complete reads, the programming and the cleaning operation. May also use a standard EPROM programmer programming and the cleaning component.
Figure 9 AM29LV800B and TMS320VC33 linking
This component is with the AMD 0.32 µ m technology manufacture, but also has the characteristic which the bypass unlocking programming and the online block protection/do not protect. The standard component provides 70, 90 and the 120ns access time, enables the high speed microprocessor operation not to wait.
Regarding reads and writes the functional device only to need the single 3.3V power source power supply. The interior produces with the adjustment programs and cleans the voltage which the operation needs. According to the AM29LV800B pin’s characteristic, it links as shown in Figure with TMS320VC33 9.
This design selects patches or strips of land as worth saving for seed the signal using the PAGE1* achievement, namely 2 (400000h~7FFFFFh) guides from the VC33 guidance to dodge saves, is because TMS320VC33 happen to maps this part of addresses exterior memory .VC33 to read as the high level, but the AM29LV800B output enables OE# effectively is the low level, must therefore add on a complementer between R and OE#. W# may with WE# direct connected, memory’s replacement pin is directly connected with the VC33 replacement pin, causes when is the VC33 replacement, dodges saves the component also to reposition, finishes the preparation for the read-write. Examines RY/BY with the XF0 achievement the status byte, because uses the character the form, therefore meets directly BYTE the high level.
In addition, the electric circuit also includes by the MAX706 design reset circuit, the watch-dog electric circuit, the monitor, the keyboard electric circuit and so on. , realizes the voltage, the electric current, the power, the mains frequency, the electrical network power factor survey. The user may carry on the man-machine conversation conveniently through the keyboard, realizes each kind of function; May see promptly through the monitor the metrical data, may preserve the empirical datum through the expanded memory unit, through asynchronous serial passes the same other computers which may facilitate unguardedly to carry on the information transmission and the data exchange completes each kind of function together. With power frequency electric quantity reflectoscope reflector which should design in practical application, the stable property, the effect is good.
Reference
[1] TMS320C3x User `s Guide Texas Instruments 1998
[2] long righteousness Lei Tianyou Cai Li Li. Floating point DSP principle and application University of Electronic Science and Technology of China publishing house 2003
[3] the MCS-51/96 series monolithic integrated circuit principle and writes using Beijing Aeronautical institute Publishing house Sun Hanfang Xu Aiqing
[4] AD Corporation ADC component data detailed list
[5] electrical energy measurement foundation China Measurement Publishing house Zhang Youshun and so on writes
Thank you so much for the information…