Source type and drain type current signal system conversion circuit supporting HART (Highway Addressable Remote Transducer)
By designing a source-type and drain-type current signal standard conversion circuit that supports HART signals, and using a voltage follower composed of a high-gain operation amplifier and transistor, the problem of incompatibility of different standard equipment is solved, high-precision signal conversion and stability improvement are achieved, and equipment waste is reduced.
Patent Information
- Application Number
- CN202422315454.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-23
- Publication Date
- 2025-09-05
- Estimated Expiration
- 2034-09-23
AI Technical Summary
The prior art has different standards of instruments and equipment in process control systems, which leads to difficulties in replacing and maintaining equipment, and the existing conversion products are not accurate and cannot meet the accuracy requirements of the control system.
A source-type and drain-type current signal conversion circuit that supports HART signals is designed, and a voltage follower composed of a high-gain operation amplifier and transistor are used to convert the current signal with high-precision through precision resistors and compensation resistors, which supports the barrier-free passage of HART signals.
It realizes high-precision conversion of signals, supports the normal passage of HART signals, reduces conversion errors, improves system stability and applicability, and reduces equipment waste.
Smart Images
Figure CN223308580U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to a conversion circuit, in particular to a source-type and leakage-type current signal format conversion circuit supporting HART. Background Art
[0002] Currently, control systems composed of DCS and PLCs dominate process control systems. Since industrial control equipment is developed by different companies and regions, while standards are becoming increasingly unified, compatibility and conversion issues between different formats are still inevitable. These include issues like active and passive AI signals, sinking and sourcing AO current signals, and NPN and PNP DI switch signals.
[0003] Common AO signal types include source and sink. Sink types are more common in equipment manufactured by Japanese and Taiwanese manufacturers, while source types are predominant in European and American equipment. Some manufacturers even design different models of equipment for both standards. The two signal formats are determined by the DCS manufacturer during circuit design, requiring different instruments to be used for matching with the actuators, and there are also significant differences in wiring.
[0004] Process equipment and facilities require long construction cycles, require significant investment, and have long lifespans. Many older devices can still function effectively with new technology and some process adjustments. Field instruments in control systems have a long lifespan, but centralized DCS systems, limited by component lifespans and computer technology, typically have a lifespan of no more than 10 years. After ten years, they can face numerous issues, including high hardware failure rates, difficulty sourcing spare parts, and slow hardware and software performance. It's common to find that original computer parts are no longer available, and the software system is incompatible with the new equipment. Therefore, DCS system upgrades are essential. Due to the differing standards used by different brands, incompatibility between upstream and downstream equipment standards is inevitable, significantly complicating system design, increasing maintenance and repair challenges, and even rendering interoperability impossible. This necessitates a standard conversion.
[0005] At present, the instrument and process control system generally adopts the method of replacing the instrument model to solve the adaptation problem. Many instruments that can still be used normally are discarded just because the signal matching is not appropriate, which will cause great waste.
[0006] Furthermore, neither domestic nor international signal conversion manufacturers offer direct products suitable for AO signal format conversion. Some manufacturers have developed signal isolation conversion products that draw power from the load circuit, meeting basic circuit conversion requirements. These isolation modules use a source input, a 4-20mA constant current source signal, with the power supply connected in series with the load. Based on circuit principles, the output closely matches the requirements of a sink-type circuit. However, the conversion accuracy of these circuit-powered isolation products is affected by load variations, limiting their use to less critical applications.
[0007] Existing passive isolation modules have poor load adaptability and cannot meet accuracy requirements. This is because the accuracy of these loop-powered conversion products is affected by load variations and reaches a range of ±0.1% / 100Ω. In control systems, load impedance is generally uncertain. Using this mode means that conversion accuracy is also uncertain and may exceed the range allowed by process control, which violates basic configuration selection principles.
[0008] Therefore, designing simple signal conversion equipment to conveniently convert signal formats is a new requirement put forward by process control systems.
[0009] To solve the above problems, the conversion of AO signals should meet five basic requirements: (1) maintain good tracking and signal response speed; (2) ensure conversion accuracy; (3) ensure stability; (4) support unimpeded passage of HART signals; and (5) control costs.
[0010] How to use a simple circuit to achieve the above five basic goals is the problem to be solved by the present invention. Summary of the Invention
[0011] In order to make up for the deficiencies of the prior art, the utility model provides a HART source and sink current signal format conversion circuit which has a simple design and can conveniently perform high-precision conversion on the signal inflow and outflow modes, while supporting the normal passage of HART signals.
[0012] The utility model is achieved through the following technical solutions:
[0013] A HART-supported source-type and sink-type current signal format conversion circuit includes a signal input positive terminal, a signal input negative terminal, a power supply positive terminal, and a power supply negative terminal. The circuit is characterized in that: an input-side precision resistor is connected and installed between the signal input positive terminal and the signal input negative terminal, the signal input positive terminal is connected to the positive input terminal of an operational amplifier, the negative input terminal of the operational amplifier is connected to the output-side precision resistor via resistor A, and the output terminal of the operational amplifier is connected to the base of a transistor via resistor B; the emitter of the transistor is connected to the output-side precision resistor, the other end of the output-side precision resistor is connected to the power supply negative terminal, a compensation resistor is connected in parallel to the output-side precision resistor, and the output-side precision resistor and the compensation resistor are connected in parallel to the signal input negative terminal; the collector of the transistor is connected to a voltage-limiting resistor, and the voltage-limiting resistor is connected to the power supply positive terminal via a load current-limiting resistor.
[0014] This conversion circuit uses a precision resistor on the input side to convert a 4-20mA current signal into a 1-5V voltage signal at the front end. This voltage-to-current circuit then converts the voltage signal into a current signal. In this voltage-to-current circuit, the output of an operational amplifier is connected to the base of a transistor, the emitter of which is connected to the precision resistor on the output side. Simultaneously, the negative input of the operational amplifier is connected to the precision resistor on the output side via resistor A, and the collector of the transistor is connected to a voltage-limiting resistor. Combined with the load current-limiting resistor, this achieves the goal of voltage-to-current conversion.
[0015] The better technical solution of the present utility model is:
[0016] A capacitor is connected between the positive terminal of the signal input and the output side of the load current limiting resistor, which allows the HART signal to pass through unimpeded, making it easier for the system AO card to read the HART signal of the on-site load and perform equipment debugging.
[0017] The input side precision resistor and the output side precision resistor are both 250 ohm resistors, resistor A and resistor B are both 4.7k resistors, and the compensation resistor is a 10-100k resistor; it is suitable for the conversion problem of 4-20mA current signal.
[0018] The reason for the transistor current amplification causes a deviation between the designed current and the collector current. The relationship between the transistor's emitter current Ie, collector current Ic and base current Ib is Ie=Ic+Ib. Therefore, a shunt resistor is connected in parallel to the precision resistor on the output side to perform precision compensation and reduce conversion error. The higher the transistor amplification factor, the smaller the conversion error.
[0019] The system conversion circuit is loaded on a single-power supply multiplier amplifier chip. The amplifier chip has high gain, low power consumption, low input offset voltage and offset current, and is suitable for the load of the circuit.
[0020] The utility model has a simple circuit design and adopts a voltage follower composed of a high-gain operational amplifier to perform precise conversion of current formats. It has high conversion accuracy, supports barrier-free passage of HART signals, operates stably, and is suitable for wide promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The present invention will be further described below with reference to the accompanying drawings.
[0022] Figure 1 It is a structural diagram of the utility model;
[0023] Figure 2 Schematic diagram of the signal isolation conversion product structure for taking power from the existing load circuit;
[0024] Figure 3 Circuit schematic diagram of a signal isolation and conversion product that draws power from an existing load circuit.
[0025] In the figure, 1 is the input side precision resistor, 2 is the operational amplifier, 3 is the capacitor, 4 is the load current limiting resistor, 5 is the transistor, 6 is the voltage limiting resistor, 7 is the output side precision resistor, 8 is the resistor A, 9 is the resistor B, 10 is the compensation resistor, 11 is the signal input positive terminal, 12 is the signal input negative terminal, 13 is the power supply positive terminal, 14 is the power supply negative terminal, Ib is the base current, Ic is the collector current, and Ie is the emitter current. DETAILED DESCRIPTION
[0026] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, the following detailed description of specific embodiments of the present invention is provided in conjunction with the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.
[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of this invention are intended only to describe specific embodiments and are not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0028] The utility model is described in detail below with reference to the accompanying drawings: This embodiment includes a signal input positive terminal 11, a signal input negative terminal 12, a power supply positive terminal 13 and a power supply negative terminal 14. An input side precision resistor 1 is connected and installed between the signal input positive terminal 11 and the signal input negative terminal 12. The signal input positive terminal 11 is connected to the positive input terminal of the operational amplifier 2, and the negative input terminal of the operational amplifier 2 is connected to the output side precision resistor 7 through the resistor A8. The output terminal of the operational amplifier 2 is connected to the base of the transistor 5 through the resistor B9; the emitter of the transistor 5 is connected to the output side precision resistor 7, and the other end of the output side precision resistor 7 is connected to the power supply negative terminal 14. A compensation resistor 10 is connected in parallel to the output side precision resistor 7, and the output side precision resistor 7 and the compensation resistor 10 are connected in parallel to the signal input negative terminal 12; the collector of the transistor 5 is connected to the voltage limiting resistor 6, and the voltage limiting resistor 6 is connected to the power supply positive terminal 14 through the load current limiting resistor 4.
[0029] The standard conversion circuit of the present invention uses a high-gain, low-power, low-input offset voltage and offset current, single-current multiplier amplifier chip LM324 as a load. The front end of the standard conversion circuit uses a 250-ohm input-side precision resistor 1 to convert the 4-20mA current signal into a 1-5V voltage signal, and then uses a voltage-to-current circuit to convert the voltage signal into a current signal. The above conversion process forms a source-drain conversion based on the load and power supply positions.
[0030] The source input of the present invention is a constant current source circuit. Since one side of the load current limiting resistor 4 is already connected to the positive terminal 14 (DC24V) of the power supply, the load current limiting resistor 4 cannot be directly connected in series between the emitter of the transistor 5 and the 250 ohm output-side precision resistor 7, but must be placed on the collector input side of the transistor 5.
[0031] Since the load current limiting resistor 4 and the output side precision resistor 7 are respectively on the collector and emitter sides of the transistor 5, the currents are not equal. The deviation is the base current Ib. Therefore, the influence of Ib is reduced by shunting the current with a parallel compensation resistor 10. The compensation resistor ÷ 250 is equal to the transistor amplification factor, which can just shunt Ib.
[0032] This is because transistor 5's current amplification causes a deviation between emitter current Ie and collector current Ic. The relationship among emitter current Ie, collector current Ic, and base current Ib is Ie = Ic + Ib. Therefore, a compensation resistor 10 (a 10-100k resistor) is connected in parallel with output-side precision resistor 7 to provide precision compensation and reduce conversion error. The higher the transistor's amplification factor, the smaller the conversion error, thus achieving precise conversion of voltage signals to current signals.
[0033] The utility model connects a capacitor 3 between the signal input positive terminal 11 and the output side of the load current limiting resistor 4, which allows the HART signal to pass through without obstruction, making it easier for the system AO card to read the HART signal of the on-site load and perform equipment debugging.
[0034] The resistor A8 and the resistor B9 of the present invention are both 4.7k resistors, which are used to set chip pointers in the circuit of the present invention, thereby improving the gain and stability of the operational amplifier 2.
[0035] As attached Figure 2-3 As shown in the figure, existing signal isolation and conversion products that draw power from the load circuit can meet basic circuit conversion requirements. The input of this isolation module is a source type, a 4-20mA constant current source signal. The power supply is connected in series with the load. From the circuit principle, the output is close to the requirements of a sink type circuit. However, the conversion accuracy of this type of isolation product with circuit power is affected by load variations, and it can only be used in non-critical applications where precision is not a priority.
[0036] In contrast, the present invention provides a simple current conversion circuit that can conveniently perform high-precision conversion on the signal inflow and outflow mode, while supporting the normal passage of HART signals. It mainly solves the problem of converting the direction of the 4-20mA current signal, from source type to sink type, and uses a voltage follower composed of a high-gain operational amplifier to perform precise current conversion, and improves the conversion accuracy through precision compensation resistors.
[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.
Claims
1. A HART-supported source-to-sink current signal format conversion circuit, comprising a signal input positive terminal (11), a signal input negative terminal (12), a power supply positive terminal (13) and a power supply negative terminal (14), characterized in that: An input side precision resistor (1) is connected between the signal input positive terminal (11) and the signal input negative terminal (12), the signal input positive terminal (11) is connected to the positive input terminal of the operational amplifier (2), the negative input terminal of the operational amplifier (2) is connected to the output side precision resistor (7) through the resistor A (8), and the output terminal of the operational amplifier (2) is connected to the base of the transistor (5) through the resistor B (9); the emitter of the transistor (5) is connected to the output side precision resistor (7), the other end of the output side precision resistor (7) is connected to the negative terminal of the power supply (14), the output side precision resistor (7) is connected in parallel with the compensation resistor (10), and the output side precision resistor (7) and the compensation resistor (10) are connected in parallel to the signal input negative terminal (12); the collector of the transistor (5) is connected to the voltage limiting resistor (6), and the voltage limiting resistor (6) is connected to the positive terminal of the power supply (13) through the load current limiting resistor (4).
2. The HART-supported source-sink current signal conversion circuit according to claim 1, wherein: A capacitor (3) is connected between the signal input positive terminal (11) and the output side of the load current limiting resistor (4).
3. The HART-supported source-sink current signal conversion circuit according to claim 1, wherein: The input side precision resistor (1) and the output side precision resistor (7) are both 250 ohm resistors, the resistor A (8) and the resistor B (9) are both 4.7k resistors, and the compensation resistor (10) is a 10-100k resistor.
4. The HART-supported source-sink current signal conversion circuit according to claim 1, wherein: The relationship among the emitter current Ie, the collector current Ic and the base current Ib of the transistor (5) is Ie=Ic+Ib.
5. The HART-supported source-sink current signal conversion circuit according to claim 1, wherein: The system conversion circuit is loaded on a single-power supply multiplication amplifier chip.