Two-wire system HART instrument device based on software decoding
By using a software-based decoding design and a microprocessor to perform signal processing on a two-wire HART instrument, the problems of hardware complexity and high cost in existing technologies are solved, achieving the effect of simplifying hardware and reducing costs.
Patent Information
- Application Number
- CN202423234397.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-26
- Publication Date
- 2025-12-26
- Estimated Expiration
- 2034-12-26
AI Technical Summary
Existing two-wire HART instrument designs require multiple chips, resulting in complex hardware and high costs.
The design adopts software decoding, which uses a microprocessor to realize signal processing, receiving and transmitting functions, reducing the dependence on hardware codec chips. HART signal processing is realized through signal separation, demodulation and modulation modules.
It simplifies hardware design, reduces costs, and significantly lowers communication error rates.
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Figure CN223729758U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to two line system instrument field, especially a two line system HART instrument device based on software decoding. BACKGROUND
[0002] Hart signal follows Bell 202 frequency shift keying (FSK) standard, is composed of two different frequency sine waves of 1200Hz and 2200Hz, and 1200Hz represents 1, 2200Hz represents 0, and in the conversion process of 1 to 0 or 0 to 1, the phase is continuous.
[0003] With the continuous development of domestic chips, the instrument localization is paid more and more attention, and localization can not only reduce cost, but also better protect intellectual property rights, but in some application occasions, for example, two line system Hart instrument, most designs adopt MCU chip, Hart Modem chip and DAC chip to realize the design of Hart signal and loop current, and the hardware is complex and the cost is expensive.
[0004] The two line system Hart instrument at present is basically composed of MCU chip, Hart Modem chip and DAC chip, the MCU chip completes the control measurement and other related functions of the whole instrument, the Hart Modem chip completes the encoding and decoding functions of Hart signal, and the DAC chip completes the loop power supply and loop current output functions, and the whole design needs three chips to complete the functions of the whole instrument, and the hardware is complex and the cost is expensive. UTILITY MODEL CONTENTS
[0005] The utility model aims at providing a two line system HART instrument device based on software decoding, and mainly solves the problems in the prior art.
[0006] In order to realize the above-mentioned purpose, the utility model adopts the technical scheme of providing a two line system HART instrument device based on software decoding, and is characterized by comprising a signal processing unit, a signal receiving unit, a signal sending unit and a power supply unit.
[0007] The signal processing unit is a microprocessor, the power supply unit is electrically connected to the signal processing unit, the input of the signal processing unit is connected to the signal receiving unit, the output of the signal processing unit is connected to the signal sending unit, and the signal receiving unit and the signal sending unit are connected to the instrument control loop.
[0008] Further, the signal receiving unit comprises a signal separation module and a signal demodulation module; the signal separation module is a direct current isolation capacitor, one end of which is connected to the instrument control loop, and the other end of which is connected to the signal demodulation module; the signal demodulation module is further electrically connected to the signal processing unit.
[0009] Further, the signal demodulation module comprises a first filter, a first voltage comparator and a second voltage comparator; the first filter is a low-pass filter; the input of the first filter is connected to the signal separation module, and the output thereof is connected to the first voltage comparator and the second voltage comparator; the output of the first voltage comparator is connected to the signal processing unit; and the output of the second voltage comparator is connected to the signal processing unit.
[0010] Further, the signal sending unit comprises a signal modulation module, a loop control module, a signal synthesis module and a loop current generation module; the signal processing unit is connected to the signal modulation module and the loop control module; the signal modulation module and the loop control module are simultaneously connected to the input of the signal synthesis module; the output of the signal synthesis module is connected to the loop current generation module; and the loop current generation module is connected to the instrument control loop.
[0011] Further, the signal modulation module is a first square wave generator, a second square wave generator and a second filter; the signal processing unit is connected to the first square wave generator and the second square wave generator; the output of the first square wave generator and the second square wave generator is connected to the input of the second filter; and the output of the second filter is connected to the signal synthesis module.
[0012] Further, the second filter is an RC charging and discharging circuit.
[0013] Further, the loop control module comprises a pulse width modulation direct current voltage output device and a third filter; the signal processing unit is connected to the input of the pulse width modulation direct current voltage output device; the output of the pulse width modulation direct current voltage output device is connected to the input of the third filter; the output of the third filter is connected to the signal synthesis module; and the third filter is a low-pass filter.
[0014] Further, the loop current generation module comprises a voltage-to-current converter and a current amplifier; the input of the voltage-to-current converter is connected to the signal synthesis module, and the output thereof is connected to the instrument control loop through the current amplifier.
[0015] Further, the current amplifier is a Darlington tube.
[0016] Further, the power taking unit is a direct current voltage converter; the direct current voltage converter is connected with the input of the instrument control circuit and the output is connected with the power input end of the signal processing unit.
[0017] In view of the above technical features, the two-wire HART instrument device based on software decoding has the following obvious advantages compared with the prior art.
[0018] 1. The microprocessor is used for processing Hart signal, and hardware coding and decoding chip is not needed, so that the cost can be reduced, and the communication error rate is extremely low.
[0019] 2. The functions realized by the Hart Modem and the DAC can be integrated into a microprocessor, and the Hart Modem and the DAC are saved, so that the hardware design and the cost are further simplified. BRIEF DESCRIPTION OF DRAWINGS
[0020] Figure 1 is a system block diagram of a preferred embodiment of the two-wire HART instrument device based on software decoding of the utility model;
[0021] Figure 2 is an electrical connection schematic diagram of a preferred embodiment of the two-wire HART instrument device based on software decoding of the utility model;
[0022] Figure 3 is an electrical connection schematic diagram of the signal demodulation module in a preferred embodiment of the two-wire HART instrument device based on software decoding of the utility model;
[0023] Figure 4 is a signal processing schematic diagram of the signal modulation module in a preferred embodiment of the two-wire HART instrument device based on software decoding of the utility model;
[0024] Figure 5 is an electrical connection schematic diagram of the signal modulation module in a preferred embodiment of the two-wire HART instrument device based on software decoding of the utility model.
[0025] In the figure: 100 - signal processing unit, 200 - signal receiving unit, 300 - signal sending unit, 400 - power taking unit;
[0026] 210 - signal separation module;
[0027] 220 - signal demodulation module; 221 - first filter, 222 - first voltage comparator, 223 - second voltage comparator;
[0028] 310 - signal modulation module; 311 - first square wave generator, 312 - second square wave generator, 313 - second filter;
[0029] 320 - loop control module; 321 - pulse width modulation DC voltage outputter, 322 - third filter;
[0030] 330 - signal synthesis module;
[0031] 340 - loop current generation module; 341 - voltage current converter, 342 - current amplifier. DETAILED DESCRIPTION
[0032] The utility model will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the utility model and not to limit the scope of the utility model. In addition, it should be understood that after reading the content taught by the utility model, those skilled in the art can make various changes or modifications to the utility model, and these equivalent forms also fall within the scope defined by the appended claims of the present application.
[0033] In the instrument control loop, the HART current signal is a small voltage AC current signal, and the loop current is a high voltage DC signal. The HART current signal is superimposed on the loop current, and together through the instrument control loop is connected to each instrument. The HART current signal encodes various control information, and the size of the loop current itself constitutes a control signal for the instrument.
[0034] Please refer to Figure 1 and Figure 2 The utility model discloses a two-wire system HART instrument device based on software decoding. As shown, a preferred embodiment thereof includes a signal processing unit 100, a signal receiving unit 200, a signal sending unit 300 and a power taking unit 400.
[0035] The signal processing unit 100 is the core component of the utility model, is a microprocessor, specific model is GD32F103. It utilizes the power taking unit 400 and provides power support from the instrument control loop, according to HART protocol stack analysis completes the software decoding of HART current signal, and obtains HART response data. The power taking unit 400 is a DC voltage converter, specifically, it is a low noise low dropout linear regulator, meets 10 to 30V input, 3.3V output. It is connected to the voltage of 12V or 24V of the instrument control loop, after taking power from the instrument control loop, voltage conversion is carried out, and the voltage (3.3V) suitable for the signal processing unit 100 is obtained, as the power supply of the signal processing unit 100. The signal processing unit 100 is also connected to the signal receiving unit 200 and the signal sending unit 300. The signal receiving unit 200 is connected to the instrument control loop, separates the alternating current part and the direct current part in the loop current, thereby obtaining the HART current signal in the form of sinusoidal wave current. However, the signal processing unit 100 is a digital circuit, and cannot directly process the sinusoidal wave alternating current signal, therefore the signal receiving unit 200 also needs to further process the HART current signal, forms the digital signal in the form of square wave after demodulation, and then can be delivered to the signal processing unit 100. Similarly, the HART response data obtained by the signal processing unit 100 according to the protocol is also a digital signal, therefore needs to utilize the signal sending unit 300 to convert the HART response data from digital form to the HART current signal in the form of sinusoidal wave current again, and modulates to the loop current, so that the two-wire instrument connected on the instrument control loop can receive the HART response data.
[0036] Please refer to Figure 1 and Figure 3The signal receiving unit 200 is composed of a signal separating module 210 and a signal demodulating module 220. The signal separating module 210 is a DC blocking capacitor, which allows AC circuit signal to pass through but blocks DC circuit current, thus separating the AC current signal from the loop current on the instrument control loop. The separated AC current signal is sent to the signal demodulating module 220 for further demodulation. The signal demodulating module 220 is composed of a first filter 221, a first voltage comparator 222 and a second voltage comparator 223. The first filter 221 is a Salley-Key filter, which is a low pass filter with a cut-off frequency of 4000 Hz. The signal demodulating module 220 uses the first filter 221 to filter the AC current signal, allowing only the AC current signal related to the HART current signal frequency to pass, thus filtering out the noise in the AC current signal and leaving only the HART current signal. The HART current signal is sent to the first voltage comparator 222 and the second voltage comparator 223 at the same time. The first voltage comparator 222 is a simple voltage comparator that detects whether there is a carrier signal in the HART current signal. It works according to a set threshold voltage (140 mV): when the input voltage is less than the threshold voltage, the output is low; otherwise, the output is high. The output of the first voltage comparator 222 is connected to the interrupt processing module of the signal processing unit 100 (microprocessor), which is used to inform the signal processing unit 100 that the carrier signal has been detected and that the data signal should be captured. The second voltage comparator 223 is a zero-crossing detection voltage comparator, whose output flips every time the input voltage crosses zero: either jumping from low to high or from high to low. In this way, the second voltage comparator 223 converts the sinusoidal signal into a square wave form of the data signal and sends it to the input capture module of the signal processing unit 100. To save power and simplify logic, in this embodiment, the input capture module of the signal processing unit 100 is triggered to work by the interrupt processing module, i.e. it only starts to work after receiving a valid carrier signal. The signal processing unit 100 uses the input interrupt module and the input capture module to capture the interval time between edges, which corresponds to 1200 Hz or 2200 Hz in the HART signal, thus demodulating the HART signal.
[0037] The signal sending unit 300 is composed of a signal modulating module 310, a loop control module 320, a signal synthesizing module 330 and a loop current generating module 340.
[0038] Please refer to Figure 1 and Figure 4 and Figure 5The signal modulation module 310 is responsible for converting the digital form of HART response data given by the signal processing unit 100 into the sinusoidal voltage form of HART control signal. It is composed of a first square wave generator 311, a second square wave generator 312 and a second filter 313. The first square wave generator 311 generates a low voltage square wave, and the second square wave generator 312 generates a high voltage square wave. Both the first square wave generator 311 and the second square wave generator 312 are controlled by the signal processing unit 100. At each time a new HART control signal is generated, the signal processing unit 100 will make the first square wave generator 311 act earlier than the second square wave generator 312, so as to produce a leading low voltage square wave and a lagging high voltage square wave. The second filter 313 is an RC charging and discharging circuit. Through the characteristics of charging and discharging, it is known that charging or discharging is fast at the beginning, and then gradually slows down. In order to modulate a sinusoidal wave, multiple voltages need to be combined at a fixed time to form an irregular staircase wave, and then the staircase wave can be perfectly changed into a sinusoidal wave after charging and discharging. The combination of the leading low voltage square wave and the lagging high voltage square wave is used to form such an irregular staircase wave. After the RC charging and discharging circuit of the second filter 313 charges and discharges the input square wave, the frequencies inconsistent with the HART current signal are filtered out, and a sinusoidal wave with an amplitude of 3.3V corresponding to the voltage domain of the microprocessor IO is formed. Then, the 3.3V sinusoidal wave is reduced by 33 times through voltage dividing resistance to become a sinusoidal wave with an amplitude of 0.1, which is used as a HART control signal.
[0039] The loop control module 320 is composed of a pulse width modulation DC voltage outputter 321 and a third filter 322, which generates a DC voltage control signal for controlling the generation of DC loop current. The loop control information output by the signal processing unit 100 is a pulse width modulation signal, which is used as the control input of the pulse width modulation DC voltage outputter 321. When the pulse width modulation signal changes, the pulse width modulation DC voltage outputter 321 charges and discharges a number of RC circuits, so as to keep them at a stable DC voltage. According to the different duty cycles of the pulse width modulation signal, the amplitude of the output voltage signal also changes from 0 to 2.5V. Different amplitude voltage signals will finally correspond to different sizes of DC loop current in the loop current generation module 340. In order to ensure the stability of the control, the pulse width modulation DC voltage outputter 321 is connected to the third filter 322, which filters out the alternating component, thereby forming a DC voltage control signal with a size amplitude controlled by the signal processing unit 100.
[0040] The signal synthesis module 330 is an operational amplifier, the bias voltage of which is below 1mV, and the bias current of which is below 1nA. The operational amplifier constitutes an adding current, the input ends of which are connected to the signal modulation module 310 and the loop control module 320 respectively, and the HART control signal output by the signal modulation module 310 and the direct current voltage control signal output by the loop control module 320 are combined to form the loop current control signal in which the HART control signal (a sine wave with an amplitude of 0.1V) with small fluctuations is superimposed on the direct current signal (a direct current voltage of 0-2.5V).
[0041] The loop current generation module 340 is composed of a voltage-to-current converter 341 and a current amplifier 342. The input of the voltage-to-current converter 341 is the loop current control signal from the signal synthesis module 330. The voltage-to-current converter 341 converts the loop current control signal in voltage form into a current signal, which is then sent to the current amplifier 342 for amplification, so as to obtain the loop current in which the alternating HART current signal is modulated on the direct current loop current, which is transmitted to the two-wire instrument through the instrument control loop. In the embodiment, the voltage-to-current converter 341 is a voltage dividing resistor, and the current amplifier 342 is a Darlington tube working in the amplification zone. When the loop current control signal flows through the voltage dividing resistor, a current matching the loop current control signal is obtained, the intensity of which is in the order of microamperes, about 0-250uA±5uA. Then, the current is amplified by 100 times through the Darlington tube, so as to obtain the loop current in the order of milliamperes. Considering the power consumption of the instrument itself, the final loop current is about 4-25mA±0.5mA. The design that the power consumption of each stage of circuit in the two-wire instrument is reduced to the order of microamperes can effectively reduce the power consumption. The amplitude of the direct current voltage control signal determines the size of the direct current loop current. The voltage amplitude of the HART control signal determines the size of the HART current signal. The superposition of the direct current loop current and the HART current signal forms the loop current.
[0042] The above only describes the preferred embodiments of the present application, and does not limit the patent range of the present application. Any equivalent structure or equivalent process transformation according to the content of the present application specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection range of the present application.
Claims
1. A software-decoding based two-wire HART instrument device, characterized by, The application relates to a signal processing device, which comprises a signal processing unit, a signal receiving unit, a signal sending unit and a power taking unit; the signal processing unit is a microprocessor; the power taking unit is electrically connected to the signal processing unit; the input of the signal processing unit is connected to the signal receiving unit; the output of the signal processing unit is connected to the signal sending unit; the signal receiving unit and the signal sending unit are connected to an instrument control loop.
2. The software-decoding based two-wire HART instrument device of claim 1, wherein, The signal receiving unit comprises a signal separation module and a signal demodulation module; the signal separation module is a direct-current capacitor, one end of which is connected to the instrument control loop, and the other end of which is connected to the signal demodulation module; the signal demodulation module is further electrically connected to the signal processing unit.
3. The software-decoding based two-wire HART instrument device of claim 2, wherein, The signal demodulation module comprises a first filter, a first voltage comparator and a second voltage comparator; the first filter is a low-pass filter; the input of the first filter is connected to the signal separation module, and the output of the first filter is connected to the first voltage comparator and the second voltage comparator; the output of the first voltage comparator is connected to the signal processing unit; the output of the second voltage comparator is connected to the signal processing unit.
4. The software-decoding based two-wire HART instrument device of claim 1, wherein, The signal sending unit comprises a signal modulation module, a loop control module, a signal synthesis module and a loop current generation module; the signal processing unit is connected to the signal modulation module and the loop control module; the signal modulation module and the loop control module are simultaneously connected to the input end of the signal synthesis module; the output of the signal synthesis module is connected to the loop current generation module; and the loop current generation module is connected to the instrument control loop.
5. The software-decoding based two-wire HART instrument device of claim 4, wherein, The signal modulation module is a first square wave generator, a second square wave generator and a second filter; the signal processing unit is connected to the first square wave generator and the second square wave generator; the output of the first square wave generator and the second square wave generator is connected to the input of the second filter; and the output of the second filter is connected to the signal synthesis module.
6. The software-decoding based two-wire HART instrument device of claim 5, wherein, The second filter is an RC charging and discharging circuit.
7. The software-decoding based two-wire HART instrument device of claim 4, wherein, The loop control module comprises a pulse width modulation direct-current voltage output device and a third filter; the input of the pulse width modulation direct-current voltage output device is connected to the signal processing unit; the output of the pulse width modulation direct-current voltage output device is connected to the input of the third filter; the output of the third filter is connected to the signal synthesis module; and the third filter is a low-pass filter.
8. The software-decoding based two-wire HART instrument device of claim 4, wherein, The loop current generation module comprises a voltage-to-current converter and a current amplifier; the input of the voltage-to-current converter is connected to the signal synthesis module, and the output of the voltage-to-current converter is connected to the instrument control loop through the current amplifier.
9. The software-decoding based two-wire HART instrument device of claim 8, wherein, The current amplifier is a Darlington tube.
10. The software-decoding based two-wire HART instrument device of claim 1, wherein, The power taking unit is a direct-current voltage converter; the input of the direct-current voltage converter is connected to the instrument control loop, and the output of the direct-current voltage converter is connected to the power supply input end of the signal processing unit.