Process Engineering Division – Instrumentation and Automation Section – Daily Topics – Topic No. 2021-01-14
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Process Engineering Division – Instrumentation and Automation Section – Daily Topics – Topic No. 2021-01-14: Discussion question: 357. What are the advantages of using the HART protocol or other similar protocols between control systems and field instruments and valves? Could you talk about any successful experiences or lessons learned?
An open communication protocol for HART-addressable remote sensor high-speed channels. HART communication uses a half-duplex mode of transmission; its feature is that it enables digital signal communication over existing analog signal lines, and it represents a transitional solution in the shift from analog systems to digital systems. HART specifies a series of commands that operate in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions commonly used by field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously.
The use of the HART protocol or other similar protocols between control systems and field instruments and valves enables timely monitoring of operational conditions on site. HART communication employs a half-duplex mode; its feature is that it allows digital signal transmission over existing analog signal lines, making it a transitional solution in the shift from analog systems to digital systems. HART specifies a series of commands that operate in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions commonly used by field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously.
HART (Highway Addressable Remote Transducer, an addressable remote sensor high-speed interface) is an open communication protocol introduced in 1985 by the American company Rosement; it is used for communication between field smart instruments and equipment in control rooms. HART devices provide communication with a relatively low bandwidth and moderate response times. After more than 10 years of development, HART technology has become highly mature abroad and has emerged as the industry standard for smart instruments worldwide. 1. Transmission principle of the HART protocol
The HART protocol utilizes FSK (Frequency Shift Keying) signals based on the Be11202 standard. It superimposes an audio digital signal with an amplitude of 0.5 mA onto a low-frequency 4–20 mA analog signal, enabling bidirectional digital communication at a data transmission rate of 1.2 Mbps. Since the average value of the FSK signal is 0, it does not affect the magnitude of the analog signal transmitted to the control system, thus ensuring compatibility with existing analog systems. In HART protocol communication, the main variables and control information are transmitted via 4-20mA analog signals; when necessary, additional measurement data, process parameters, device configuration, calibration, and diagnostic information are accessed through the HART protocol. 2. Three types of commands in the HART protocol HART communication uses a half-duplex mode; its feature is that it enables digital signal transmission over existing analog signal lines. It represents a transitional solution in the shift from analog systems to digital systems, and therefore possesses strong market competitiveness during this transition period, which has led to its rapid development. HART specifies a series of commands and operates in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions for the most commonly used field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously. 3. Advantages of the HART protocol: ① HART uses a unified device description language called DDL. Equipment manufacturers use this standard language to describe the characteristics of their devices, and the HART Foundation is responsible for registering and managing these device descriptions, compiling them into a device description dictionary. The master device utilizes DDL technology to understand the characteristic parameters of these devices, thereby avoiding the need to develop specialized interfaces for them. However, due to this mixed analog-digital signal system, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can utilize bus power supply, meets intrinsic safety and explosion-proof requirements, and can form a dual-master system with a handheld programmer and a management system host serving as the master devices. ②The HART protocol enables two-way transmission of digital information, while analog signals allow only one-way transmission of data, either from the device to the host (input) or from the host to the device (output). The HART protocol enables two-way transmission of digital information. This breaks away from the traditional approach where instruments could only receive control commands from the main unit – such as for valve control – and also allows them to transmit information about the status of the valves back to the main unit. Similarly, while in the past only process variables could be sent to the monitoring computer, it can now also receive information such as configuration settings. ③A large amount of information needs to be transmitted. Traditional analog and discrete devices can only communicate using a single process variable – making it difficult to find an easy way to determine whether the transmitted information is valid. Using HART makes it possible to obtain not only process variables, but also other types of information. Each HART device contains 35–40 standard information items, such as device status, diagnostic alarms, process variables, units, loop current, percentage range, manufacturer, and device label. Other information includes the ability of the host to query the HART device digitally in order to determine whether the device’s settings are correct and whether it is operating properly. This feature eliminates most routine inspection tasks and helps to detect process failures before they cause serious problems. ④Multi-variable processing is supported; in digital communication mode, a pair of cables can handle multiple variables. For example, a transmitter can process inputs from multiple sensors. 4 process variables can be handled in one message. In any field instrument, the HART protocol supports 256 process variables. ⑤Foundation management: When using HART, users are not constrained by any particular supplier or local \"standard\". This is because HART technology does not belong to any single company, nor is it under the control of a particular standard-setting organization. In fact, this technology is managed by the unaffiliated non-profit organization HART Communication Foundation. ⑥Widely applied: In the field of process industries, HART is currently the most widely used protocol in the world. Nearly several hundred products using HART technology are available from various suppliers. The wide range of products means that HART products can meet the needs of almost all process applications, and it is also possible to choose the most suitable one from a variety of dealers’ products. ⑦Full interoperability: Full interoperability means that HART-compatible products from any supplier can work together with the main system. It is compatible with HART devices; some host systems use uniformly formatted commands, while more advanced systems employ device descriptions to understand all HART information.
The HART protocol utilizes FSK (Frequency Shift Keying) signals based on the Be11202 standard. It superimposes an audio digital signal with an amplitude of 0.5 mA onto a low-frequency 4–20 mA analog signal, enabling bidirectional digital communication at a data transmission rate of 1.2 Mbps. Since the average value of the FSK signal is 0, it does not affect the magnitude of the analog signal transmitted to the control system, thus ensuring compatibility with existing analog systems. In HART protocol communication, the main variables and control information are transmitted via 4-20mA analog signals; when necessary, additional measurement data, process parameters, device configuration, calibration, and diagnostic information are accessed through the HART protocol. 2. Three types of commands in the HART protocol HART communication uses a half-duplex mode; its feature is that it enables digital signal transmission over existing analog signal lines. It represents a transitional solution in the shift from analog systems to digital systems, and therefore possesses strong market competitiveness during this transition period, which has led to its rapid development. HART specifies a series of commands and operates in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions for the most commonly used field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously. 3. Advantages of the HART protocol: ① HART uses a unified device description language called DDL. Equipment manufacturers use this standard language to describe the characteristics of their devices, and the HART Foundation is responsible for registering and managing these device descriptions, compiling them into a device description dictionary. The master device utilizes DDL technology to understand the characteristic parameters of these devices, thereby avoiding the need to develop specialized interfaces for them. However, due to this mixed analog-digital signal system, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can utilize bus power supply, meets intrinsic safety and explosion-proof requirements, and can form a dual-master system with a handheld programmer and a management system host serving as the master devices. ②The HART protocol enables two-way transmission of digital information, while analog signals allow only one-way transmission of data, either from the device to the host (input) or from the host to the device (output). The HART protocol enables two-way transmission of digital information. This breaks away from the traditional approach where instruments could only receive control commands from the main unit – such as for valve control – and also allows them to transmit information about the status of the valves back to the main unit. Similarly, while in the past only process variables could be sent to the monitoring computer, it can now also receive information such as configuration settings. ③A large amount of information needs to be transmitted. Traditional analog and discrete devices can only communicate using a single process variable – making it difficult to find an easy way to determine whether the transmitted information is valid. Using HART makes it possible to obtain not only process variables, but also other types of information. Each HART device contains 35–40 standard information items, such as device status, diagnostic alarms, process variables, units, loop current, percentage range, manufacturer, and device label. Other information includes the ability of the host to query the HART device digitally in order to determine whether the device’s settings are correct and whether it is operating properly. This feature eliminates most routine inspection tasks and helps to detect process failures before they cause serious problems. ④Multi-variable processing is supported; in digital communication mode, a pair of cables can handle multiple variables. For example, a transmitter can process inputs from multiple sensors. 4 process variables can be handled in one message. In any field instrument, the HART protocol supports 256 process variables. ⑤Foundation management: When using HART, users are not constrained by any particular supplier or local \"standard\". This is because HART technology does not belong to any single company, nor is it under the control of a particular standard-setting organization. In fact, this technology is managed by the unaffiliated non-profit organization HART Communication Foundation. ⑥Widely applied: In the field of process industries, HART is currently the most widely used protocol in the world. Nearly several hundred products using HART technology are available from various suppliers. The wide range of products means that HART products can meet the needs of almost all process applications, and it is also possible to choose the most suitable one from a variety of dealers’ products. ⑦Full interoperability: Full interoperability means that HART-compatible products from any supplier can work together with the main system. It is compatible with HART devices; some host systems use uniformly formatted commands, while more advanced systems employ device descriptions to understand all HART information.
HART (Highway Addressable Remote Transducer, an addressable remote sensor high-speed interface) is an open communication protocol introduced in 1985 by the American company Rosement; it is used for communication between field smart instruments and equipment in control rooms. HART devices provide communication with a relatively low bandwidth and moderate response times. After more than 10 years of development, HART technology has become highly mature abroad and has emerged as the industry standard for smart instruments worldwide. 1. Transmission principle of the HART protocol
The HART protocol utilizes FSK (Frequency Shift Keying) signals based on the Be11202 standard. It superimposes an audio digital signal with an amplitude of 0.5 mA onto a low-frequency 4–20 mA analog signal, enabling bidirectional digital communication at a data transmission rate of 1.2 Mbps. Since the average value of the FSK signal is 0, it does not affect the magnitude of the analog signal transmitted to the control system, thus ensuring compatibility with existing analog systems. In HART protocol communication, the main variables and control information are transmitted via 4-20mA analog signals; when necessary, additional measurement data, process parameters, device configuration, calibration, and diagnostic information are accessed through the HART protocol. 2. Three types of commands in the HART protocol HART communication uses a half-duplex mode; its feature is that it enables digital signal transmission over existing analog signal lines. It represents a transitional solution in the shift from analog systems to digital systems, and therefore possesses strong market competitiveness during this transition period, which has led to its rapid development. HART specifies a series of commands and operates in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions for the most commonly used field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously. 3. Advantages of the HART protocol: ① HART uses a unified device description language called DDL. Equipment manufacturers use this standard language to describe the characteristics of their devices, and the HART Foundation is responsible for registering and managing these device descriptions, compiling them into a device description dictionary. The master device utilizes DDL technology to understand the characteristic parameters of these devices, thereby avoiding the need to develop specialized interfaces for them. However, due to this mixed analog-digital signal system, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can utilize bus power supply, meets intrinsic safety and explosion-proof requirements, and can form a dual-master system with a handheld programmer and a management system host serving as the master devices. ②The HART protocol enables two-way transmission of digital information, while analog signals allow only one-way transmission of data, either from the device to the host (input) or from the host to the device (output). The HART protocol enables two-way transmission of digital information. This breaks away from the traditional approach where instruments could only receive control commands from the main unit – such as for valve control – and also allows them to transmit information about the status of the valves back to the main unit. Similarly, while in the past only process variables could be sent to the monitoring computer, it can now also receive information such as configuration settings. ③A large amount of information needs to be transmitted. Traditional analog and discrete devices can only communicate using a single process variable – making it difficult to find an easy way to determine whether the transmitted information is valid. Using HART makes it possible to obtain not only process variables, but also other types of information. Each HART device contains 35–40 standard information items, such as device status, diagnostic alarms, process variables, units, loop current, percentage range, manufacturer, and device label. Other information includes the ability of the host to query the HART device digitally in order to determine whether the device’s settings are correct and whether it is operating properly. This feature eliminates most routine inspection tasks and helps to detect process failures before they cause serious problems. ④Multi-variable processing is supported; in digital communication mode, a pair of cables can handle multiple variables. For example, a transmitter can process inputs from multiple sensors. 4 process variables can be handled in one message. In any field instrument, the HART protocol supports 256 process variables. ⑤Foundation management: When using HART, users are not constrained by any particular supplier or local \"standard\". This is because HART technology does not belong to any single company, nor is it under the control of a particular standard-setting organization. In fact, this technology is managed by the unaffiliated non-profit organization HART Communication Foundation. ⑥Widely applied: In the field of process industries, HART is currently the most widely used protocol in the world. Nearly several hundred products using HART technology are available from various suppliers. The wide range of products means that HART products can meet the needs of almost all process applications, and it is also possible to choose the most suitable one from a variety of dealers’ products. ⑦Full interoperability: Full interoperability means that HART-compatible products from any supplier can work together with the main system. It is compatible with HART devices; some host systems use uniformly formatted commands, while more advanced systems employ device descriptions to understand all HART information.
The HART protocol utilizes FSK (Frequency Shift Keying) signals based on the Be11202 standard. It superimposes an audio digital signal with an amplitude of 0.5 mA onto a low-frequency 4–20 mA analog signal, enabling bidirectional digital communication at a data transmission rate of 1.2 Mbps. Since the average value of the FSK signal is 0, it does not affect the magnitude of the analog signal transmitted to the control system, thus ensuring compatibility with existing analog systems. In HART protocol communication, the main variables and control information are transmitted via 4-20mA analog signals; when necessary, additional measurement data, process parameters, device configuration, calibration, and diagnostic information are accessed through the HART protocol. 2. Three types of commands in the HART protocol HART communication uses a half-duplex mode; its feature is that it enables digital signal transmission over existing analog signal lines. It represents a transitional solution in the shift from analog systems to digital systems, and therefore possesses strong market competitiveness during this transition period, which has led to its rapid development. HART specifies a series of commands and operates in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions for the most commonly used field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously. 3. Advantages of the HART protocol: ① HART uses a unified device description language called DDL. Equipment manufacturers use this standard language to describe the characteristics of their devices, and the HART Foundation is responsible for registering and managing these device descriptions, compiling them into a device description dictionary. The master device utilizes DDL technology to understand the characteristic parameters of these devices, thereby avoiding the need to develop specialized interfaces for them. However, due to this mixed analog-digital signal system, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can utilize bus power supply, meets intrinsic safety and explosion-proof requirements, and can form a dual-master system with a handheld programmer and a management system host serving as the master devices. ②The HART protocol enables two-way transmission of digital information, while analog signals allow only one-way transmission of data, either from the device to the host (input) or from the host to the device (output). The HART protocol enables two-way transmission of digital information. This breaks away from the traditional approach where instruments could only receive control commands from the main unit – such as for valve control – and also allows them to transmit information about the status of the valves back to the main unit. Similarly, while in the past only process variables could be sent to the monitoring computer, it can now also receive information such as configuration settings. ③A large amount of information needs to be transmitted. Traditional analog and discrete devices can only communicate using a single process variable – making it difficult to find an easy way to determine whether the transmitted information is valid. Using HART makes it possible to obtain not only process variables, but also other types of information. Each HART device contains 35–40 standard information items, such as device status, diagnostic alarms, process variables, units, loop current, percentage range, manufacturer, and device label. Other information includes the ability of the host to query the HART device digitally in order to determine whether the device’s settings are correct and whether it is operating properly. This feature eliminates most routine inspection tasks and helps to detect process failures before they cause serious problems. ④Multi-variable processing is supported; in digital communication mode, a pair of cables can handle multiple variables. For example, a transmitter can process inputs from multiple sensors. 4 process variables can be handled in one message. In any field instrument, the HART protocol supports 256 process variables. ⑤Foundation management: When using HART, users are not constrained by any particular supplier or local \"standard\". This is because HART technology does not belong to any single company, nor is it under the control of a particular standard-setting organization. In fact, this technology is managed by the unaffiliated non-profit organization HART Communication Foundation. ⑥Widely applied: In the field of process industries, HART is currently the most widely used protocol in the world. Nearly several hundred products using HART technology are available from various suppliers. The wide range of products means that HART products can meet the needs of almost all process applications, and it is also possible to choose the most suitable one from a variety of dealers’ products. ⑦Full interoperability: Full interoperability means that HART-compatible products from any supplier can work together with the main system. It is compatible with HART devices; some host systems use uniformly formatted commands, while more advanced systems employ device descriptions to understand all HART information.
HART (Highway Addressable Remote Transducer, an addressable remote sensor high-speed interface) is an open communication protocol introduced in 1985 by the American company Rosement; it is used for communication between field smart instruments and equipment in control rooms. HART devices provide communication with a relatively low bandwidth and moderate response times. After more than 10 years of development, HART technology has become highly mature abroad and has emerged as the industry standard for smart instruments worldwide. 1. Transmission principle of the HART protocol
The HART protocol utilizes FSK (Frequency Shift Keying) signals based on the Be11202 standard. It superimposes an audio digital signal with an amplitude of 0.5 mA onto a low-frequency 4–20 mA analog signal, enabling bidirectional digital communication at a data transmission rate of 1.2 Mbps. Since the average value of the FSK signal is 0, it does not affect the magnitude of the analog signal transmitted to the control system, thus ensuring compatibility with existing analog systems. In HART protocol communication, the main variables and control information are transmitted via 4-20mA analog signals; when necessary, additional measurement data, process parameters, device configuration, calibration, and diagnostic information are accessed through the HART protocol. 2. Three types of commands in the HART protocol HART communication uses a half-duplex mode; its feature is that it enables digital signal transmission over existing analog signal lines. It represents a transitional solution in the shift from analog systems to digital systems, and therefore possesses strong market competitiveness during this transition period, which has led to its rapid development. HART specifies a series of commands and operates in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions for the most commonly used field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously. 3. Advantages of the HART protocol: ① HART uses a unified device description language called DDL. Equipment manufacturers use this standard language to describe the characteristics of their devices, and the HART Foundation is responsible for registering and managing these device descriptions, compiling them into a device description dictionary. The master device utilizes DDL technology to understand the characteristic parameters of these devices, thereby avoiding the need to develop specialized interfaces for them. However, due to this mixed analog-digital signal system, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can utilize bus power supply, meets intrinsic safety and explosion-proof requirements, and can form a dual-master system with a handheld programmer and a management system host serving as the master devices. ②The HART protocol enables two-way transmission of digital information, while analog signals allow only one-way transmission of data, either from the device to the host (input) or from the host to the device (output). The HART protocol enables two-way transmission of digital information. This breaks away from the traditional approach where instruments could only receive control commands from the main unit – such as for valve control – and also allows them to transmit information about the status of the valves back to the main unit. Similarly, while in the past only process variables could be sent to the monitoring computer, it can now also receive information such as configuration settings. ③A large amount of information needs to be transmitted. Traditional analog and discrete devices can only communicate using a single process variable – making it difficult to find an easy way to determine whether the transmitted information is valid. Using HART makes it possible to obtain not only process variables, but also other types of information. Each HART device contains 35–40 standard information items, such as device status, diagnostic alarms, process variables, units, loop current, percentage range, manufacturer, and device label. Other information includes the ability of the host to query the HART device digitally in order to determine whether the device’s settings are correct and whether it is operating properly. This feature eliminates most routine inspection tasks and helps to detect process failures before they cause serious problems. ④Multi-variable processing is supported; in digital communication mode, a pair of cables can handle multiple variables. For example, a transmitter can process inputs from multiple sensors. 4 process variables can be handled in one message. In any field instrument, the HART protocol supports 256 process variables. ⑤Foundation management: When using HART, users are not constrained by any particular supplier or local \"standard\". This is because HART technology does not belong to any single company, nor is it under the control of a particular standard-setting organization. In fact, this technology is managed by the unaffiliated non-profit organization HART Communication Foundation. ⑥Widely applied: In the field of process industries, HART is currently the most widely used protocol in the world. Nearly several hundred products using HART technology are available from various suppliers. The wide range of products means that HART products can meet the needs of almost all process applications, and it is also possible to choose the most suitable one from a variety of dealers’ products. ⑦Full interoperability: Full interoperability means that HART-compatible products from any supplier can work together with the main system. It is compatible with HART devices; some host systems use uniformly formatted commands, while more advanced systems employ device descriptions to understand all HART information.
The HART protocol utilizes FSK (Frequency Shift Keying) signals based on the Be11202 standard. It superimposes an audio digital signal with an amplitude of 0.5 mA onto a low-frequency 4–20 mA analog signal, enabling bidirectional digital communication at a data transmission rate of 1.2 Mbps. Since the average value of the FSK signal is 0, it does not affect the magnitude of the analog signal transmitted to the control system, thus ensuring compatibility with existing analog systems. In HART protocol communication, the main variables and control information are transmitted via 4-20mA analog signals; when necessary, additional measurement data, process parameters, device configuration, calibration, and diagnostic information are accessed through the HART protocol. 2. Three types of commands in the HART protocol HART communication uses a half-duplex mode; its feature is that it enables digital signal transmission over existing analog signal lines. It represents a transitional solution in the shift from analog systems to digital systems, and therefore possesses strong market competitiveness during this transition period, which has led to its rapid development. HART specifies a series of commands and operates in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions for the most commonly used field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously. 3. Advantages of the HART protocol: ① HART uses a unified device description language called DDL. Equipment manufacturers use this standard language to describe the characteristics of their devices, and the HART Foundation is responsible for registering and managing these device descriptions, compiling them into a device description dictionary. The master device utilizes DDL technology to understand the characteristic parameters of these devices, thereby avoiding the need to develop specialized interfaces for them. However, due to this mixed analog-digital signal system, it is difficult to develop a communication interface chip that can meet the requirements of various companies. HART can utilize bus power supply, meets intrinsic safety and explosion-proof requirements, and can form a dual-master system with a handheld programmer and a management system host serving as the master devices. ②The HART protocol enables two-way transmission of digital information, while analog signals allow only one-way transmission of data, either from the device to the host (input) or from the host to the device (output). The HART protocol enables two-way transmission of digital information. This breaks away from the traditional approach where instruments could only receive control commands from the main unit – such as for valve control – and also allows them to transmit information about the status of the valves back to the main unit. Similarly, while in the past only process variables could be sent to the monitoring computer, it can now also receive information such as configuration settings. ③A large amount of information needs to be transmitted. Traditional analog and discrete devices can only communicate using a single process variable – making it difficult to find an easy way to determine whether the transmitted information is valid. Using HART makes it possible to obtain not only process variables, but also other types of information. Each HART device contains 35–40 standard information items, such as device status, diagnostic alarms, process variables, units, loop current, percentage range, manufacturer, and device label. Other information includes the ability of the host to query the HART device digitally in order to determine whether the device’s settings are correct and whether it is operating properly. This feature eliminates most routine inspection tasks and helps to detect process failures before they cause serious problems. ④Multi-variable processing is supported; in digital communication mode, a pair of cables can handle multiple variables. For example, a transmitter can process inputs from multiple sensors. 4 process variables can be handled in one message. In any field instrument, the HART protocol supports 256 process variables. ⑤Foundation management: When using HART, users are not constrained by any particular supplier or local \"standard\". This is because HART technology does not belong to any single company, nor is it under the control of a particular standard-setting organization. In fact, this technology is managed by the unaffiliated non-profit organization HART Communication Foundation. ⑥Widely applied: In the field of process industries, HART is currently the most widely used protocol in the world. Nearly several hundred products using HART technology are available from various suppliers. The wide range of products means that HART products can meet the needs of almost all process applications, and it is also possible to choose the most suitable one from a variety of dealers’ products. ⑦Full interoperability: Full interoperability means that HART-compatible products from any supplier can work together with the main system. It is compatible with HART devices; some host systems use uniformly formatted commands, while more advanced systems employ device descriptions to understand all HART information.
An open communication protocol for HART-addressable remote sensor high-speed channels. HART communication uses a half-duplex mode of transmission; its feature is that it enables digital signal communication over existing analog signal lines, and it represents a transitional solution in the shift from analog systems to digital systems. HART specifies a series of commands that operate in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions commonly used by field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously.
The use of the HART protocol or other similar protocols between control systems and field instruments and valves enables timely monitoring of operational conditions on site. HART communication employs a half-duplex mode; its feature is that it allows digital signal transmission over existing analog signal lines, making it a transitional solution in the shift from analog systems to digital systems. HART specifies a series of commands that operate in a command-based manner. It has three types of commands. The first type is called general commands, which are commands that all devices understand and execute ； The second category is known as general behavior commands; the functions they provide can be implemented in many field devices (though not all of them). These commands include a library of functions commonly used by field devices ； The third category is known as special device commands, which are designed to enable special functions in certain devices. Such commands can be made available for use by the community, or they can be exclusive to the company that developed them. In a field device, these three types of commands are usually found to exist simultaneously.