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Design of multi-engine speed simulator

Print View , by: iSee ,Total views: 16 ,Word Count: 2079 ,Date: Tue, 28 Jul 2009 Time: 3:57 PM

Signal generator as a measurement of electronic control systems the most common electronic control of measuring instruments, industrial control, teaching, scientific research of the basic instruments commonly used. While the market began to emerge a variety of signal generator, but it still could not shake off their bulky, buttons and more expensive, such as the shortcomings of systems engineering staff to go out to the driving force for debugging and maintenance of electronic control equipment inconvenience. Taking into account many factors, it is necessary to develop a simple structure and easy-to-use portable multi-functional simulator engine speed. It can not start the engine, the simulation for the site to generate and output the necessary speed (frequency) signal, given current signal to electronic control equipment (such as electronic governor, etc.) for debugging, can be significant savings so the cost of test (such as fuel costs, etc.), and high precision adjustment; the state of the boot can detect the frequency of the external signal (ie, engine speed signal at the scene), the numerical display and the system uses a battery-powered, so the more function of engine speed simulator will power the success of the development of systems engineering and technical personnel to conduct field tests of great convenience, and have a high practical value, economic value.

1 System Design

Multi-engine speed simulator system block diagram shown in Figure 1. It is mainly from the power supply, the frequency of signal generator, the frequency of signal conditioning, signal frequency measurement, the current signal generation, signal measurement and the current measurements show that such single-chip modules. By the frequency knob to adjust the output frequency of the standard adjustable square wave signal can be adjusted through the current knob adjustable output current signal to O ~ 20 mA, by the digital display, in addition it can detect the external input signal frequency. Mainly as a result of engine testing, so speed is the speed of measurement to another unique feature of the simulator.

Design of multi-engine speed simulator

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2 System Hardware Design

2.1 Signal Generator Circuit

(1) the frequency of signal generator circuit

Frequency signal generator circuit shown in Figure 2.

Design of multi-engine speed simulator

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The circuit module is a core component of selected LM331 voltage-frequency converter chips. It is produced by the United States NS high cost performance IC with adjustable frequency range, low non-linear, high-precision conversion can be characterized by single power supply, together with the surrounding circuitry to achieve V / F function. The frequency of the output signal can be used formula (1) calculated as follows:

fout = (Vin × R2) ÷ (2.09 × R1 × R3 × C2) (1)

Where: Vin units for V, that the U1 voltage conversion; R1, R2, R3 resistance unit Ω; C1 capacitor unit F; fout unit for Hz, the frequency of said output value of U1. Can be seen that the signal is proportional to frequency and Vin has a very good linear relationship, as long as the choice of the appropriate resistors and capacitors, and varistors W1 performance good enough, we can guarantee the stability of the output signal. Here used metal film resistors are resistors.

(2) current signal generator circuit

Current signal generator circuit shown in figure 3. The frequency of the circuit module and signal generator modules share a sliding rheostat W1. Wiring is as follows: J3-1, J3-2, J3-3, respectively, then the frequency signal generator circuit in the J1-1, J1-2, J1-3, through the selection switch to select the frequency, current regulation. Sliding rheostat regulating the value of w1 can be achieved in O ~ 20 mA current output. The circuit is a core component of the optional AD694. AD694 is a monolithic voltage-current converter (hereinafter referred to as V / I). Input voltage signal will be converted into standard O ~ 20 mA current signal, can be widely used in pressure, flow, temperature and other parameters of signal transmission, and the valve, regulator, as well as some commonly used process control equipment.

Design of multi-engine speed simulator

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2.2 the frequency of signal conditioning circuit

Frequency signal conditioning circuit shown in Figure 4. Due to the frequency signal generator circuit waveform is not generated by rules, subject to CD4013 for plastic processing, collection and finally single-chip LED display. If K1 closed, the short access to internal signals and, at this time can be achieved on the external pulse signal (for example, magnetic sensor from the diesel engine to the sinusoidal signal), because the T1 and the CD4013 will form the entire width of their ratio of 1:1 the square, the same can be collected in single-chip microcomputer. Note that the number of single-chip pulse calculation should take into account is the frequency of the pulse after the signal, so the software in terms of the doubling of the pulses.

Design of multi-engine speed simulator

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2.3 Serial A / D conversion circuit

Serial A / D conversion circuit shown in Figure 5. AD694 generated from 0 ~ 20 mA current, converted to O ~ 2. OV analog voltage signal, to connect to the CHO and MAXl44 port CHl. As the analog signal voltage range of O ~ 2. OV, therefore can be MAXl44 reference voltage set to 2.048V, this can improve the conversion accuracy, but also facilitate the conversion of the follow-up data processing. The 2.048 V reference voltage can be provided REFl91.

Design of multi-engine speed simulator

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Single-chip measurements show that 2.4 AT89C2051 Circuit

Measurements show that the core components of the circuit is AT89C2051 microcontroller, the circuit as shown in Figure 6. Watchdog reset them using MAX813L, to achieve power-on reset and procedures for monitoring (in the process to achieve); engine based on the actual number of teeth by artificial set of teeth, and by reading single-chip; MAX7219 to BCD decoder, since the role of display driver; microprocessor using Atmel's AT89C2051, with its internal procedures 2KB memory, 128 bytes of data memory, 15 I / O port, and two timers, adequate use of the multi-speed simulator.

Design of multi-engine speed simulator

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3 system software design

Software processes of the system shown in figure 7. It includes the frequency / speed measurement, serial A / D conversion value of reading, numerical display and related processing section.

Design of multi-engine speed simulator

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3.1 frequency / speed measurement software design

When a power circuit, MAX813L have a reset signal to single-chip reset, the program jump to the start address 0000h, the first MAX7219 internal registers and initialization, such as TO, T1, TMOD, then TO, T1, EXl open interrupted. statement on the cycle of Inquiry to MAX813Ltime interval should be less than 1.6 s, otherwise it will once again have a reset signal, to disrupt the normal operation of the procedure. P1.3 pin and then testing, if low, then the implementation of serial A / D conversion value of the reading process; if high, the falling edge single-chip signal is triggered at the interruption, opened T1 timing, TO count. When the T1 timer 1 s to the closure of TO, T1, read the TO value, and then on the TO, T1 open interruption, re-timing of pulses. Then calculated (T0 value multiplied by 2), to determine (when not more than 9999 or equal to O, when, as a legal and FLAG sign home), and then sent to MAX7219, after decoding by the LED display, and the frequency of indicator light to inform users that the frequency value, the necessary adjustments in accordance with intortum W1 (see Figure 2), so that the issue of the desired frequency generator signal value, which is the principle of measuring signal frequency; if the value is not legitimate, LED will be do not show or display O, at this time should be adjusted until the legitimate W1. External signal frequency measurement and display program with the former (the need to switch to reverse rotation to the input file). P2.7 pin if low, then measuring the speed of the engine needs to be in front of the frequency of speed values into the formula (2):

n = (f 60) / k (2)

Where: n for the diesel engine speed (r / min), f is the frequency of the measured value (Hz), k is the number of teeth of gear motor gun.

Single-chip reader can see the need for numerical teeth, and then calculate and determine the (n less than 9999), and sent to LED display. It must be noted that: the above mentioned first in 1 s time for the speed pulse signal to accumulate the number of counts, and then into the formula (2) the calculation speed. This measurement method is called frequency. When the engine operation in low speed, they have to use the measurement cycle: first measured the average pulse cycle, and then use division to calculate the frequency value into the speed formula to show after the jump circle of Inquiry, and then calculate the frequency value of the use of division, into the speed calculated to show after the jump circle of Inquiry, and continue to inquiries from time to time interrupted.

3.2 Serial A / D converter to read the value of software design

MAXl44 with the SCM as a result of a very simple interface, just three I / O lines can be, so the system uses SCM P1. O, P1.1, P1.2. CHID through the flag can be distinguished CHO and CHl channel, and then the high four shielding can be obtained actual A / D conversion data, the use of ANL R3, OFH high shielding 4. After the end of the program, R3 for the A / D conversion data of 12 high-4, R2 in the lower 8-bit, single-chip set and then use the conversion process (OFFFH corresponds to 2.048V, which is 20. 48 mA; 0000H corresponding to OV, that is, O mA), to display the current size.

Conclusion

The use of multi-functional device simulator engine speed less, low cost, convenient, easy to implement. Discovered through testing, as long as the resistance-capacitance low-temperature coefficient components, the output frequency, current is quite stable, and therefore cost-effective. The multi-speed indicated that the use of simulators, and its reliability and output stability, and easy to carry.


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