Hart Communication

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HART Communication Protocol is increasingly widely used in the industry as the standard communication protocol for digital devices using analog 4-20mA current form. On the market today appear more and more devices used to convert measurement protocols. Which is the main cause communication feature allows two-way communication between the user and the sensors will contribute significantly improved information management systems for technological processes in the plant. At the same time reduce the cost of installation, commissioning, operation and maintenance of equipment, thereby increasing competition for manufacturers to use this equipment.

Overview of the HART Protocol

In so many years ago, the signal standards for measuring equipment in the plant is automated analog 4-20mA current form. Which corresponds to 4mA lower limit of the measuring device, and 20mA corresponds to the limit of the measurement equipment. Assuming a device for measuring pressure sensor is the measurement from 0-100 Psi, the output is 4mA will mean that pressure is placed on the device by 0, but when 20mA current signal is then mean pressure at the sensor of the measuring device is converted to 100 psi, and similarly, a 12mA current output device in the corresponding 50Psi pressure at the inlet. Due to the high anti-interference and not altered when transmitted over a long distance than the form of pressure measurement signal: 0-5VDC, 0-10 VDC, up 4-20mA current signal has been accepted and used widely in industry.

HART protocol is based on the principle of promoting the virtues of Vietnamese 4-20mA current signal for the sensor switch smart metering. It is particularly applicable to the device using the signal lines as traditional 4-20mA. HART protocol can retain the advantages of Vietnam 4-20mA current signal, while allowing the ability to communicate two-way digital signals without affecting the measurement of features 4-20mA signal. Unlike the signaling technology of other devices using HART protocol can be used with compatible systems using 4-20mA signal traditions, and thus provides the user a The only solution to resolve compatibility issues between legacy systems and new technologies. For reasons that are known as HART and upgrade the digitized communication signals using traditional 4-20mA.

The introduction and application of the HART protocol is a very important technology for both manufacturers and users, and the strides in innovation revolution in process control technology, through raising the ability of the devices to measure and control. It enables devices become "smart" more. At the same time bring the 4-20mA signal a new role tradition. In addition to continuing to allow the device to perform the function of measuring the current signal 4-20mA, HART enabled device capable of communicating and processing information related to variable measurement, device parameters, device configuration, calibration and auto-detection and error. From systems which give them control center information and tools to manage the system.

There are already a large number of equipment manufacturers and equipment renowned technology and that number will surely one day more. So in addition to the advantages of Vietnam's new technology, HART allows people to keep and continue to communicate with the devices present in the system. In addition, the use of HART devices have proven their superiority over Vietnam in fact the convenience, simplicity of installation, operation and maintenance, to dramatically improve the efficiency of the system and create conditions comply with international standards such as ISO 9000, OSHA, EPA, DOT ... At the same time contributing to reducing the cost and improving productivity. Currently there are about 4 million devices have been installed worldwide.

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What is HART protocol?

HART - Highway Addressable Remote Transducer - Temporary service is remote switching device speed by address. HART protocol uses standard Bell 202 Frequency Shift Keying (FSK) to implement digital signal based on the 4-20mA signal as shown in Figure 1 and 2. This allows two-way communication capability to transmit / receive additional information to / from smart sensors. Communication using HART communication speed 1200bps should not affect 4-20mA signal is transmitted on the same line and allows two or more of the data being exchanged between the system control / display center with sensors. Since the FSK signal is phase continuous and not interfere with the 4-20mA signal.

HART protocol is the traditional form of the master / servant (master / slaver), mean field devices (slaver) can only communicate with the Master. HART can be used in various modes of communication to transmit information from / to the smart sensors and control systems / monitoring center. HART offers two Master (primary and secondary) as shown in Figure 3. It allows secondary master as communication devices external calibration can be used to monitor / configure the slaver-sensing device without affecting the primary Master - Control Systems / Director monitoring center. The most common application of the HART communication mode Master / slaver with vieecj simultaneously transmit 4-20 mA signal as shown in Figure 4. HART protocol allows all the digital signal communication with field devices such as point-to-point or connected in series - multidrop. Figure 5 is an example of HART communication. Whatever can also upgrade to a higher speed communications, but often the mode of communication is point-to-point applies more widely.

Because of the potential application serial multidrop configuration, the installed HART devices can be significantly reduced cost because many devices can be connected to a single pair of wires. However, this configuration is limited to the transmission parameters for analog 4-20mA is fixed. Therefore usually only use serial configuration in case of wiring required savings in long distance, then we can use a pair of wires for all signals instead of lots of wires running parallel pair as shown in Figure 6.

HART Command Set is organized into 3 groups and provides access to read / write information from / to the sensors:

Universal Command must be done by using HART devices and provide the ability to communicate between individual devices and the different caves using this technology. Universal Command provides the ability to access the general information useful for the operation of equipment such as manufacturer name, device name, model number, description, measurement range, measurement variables.

Practice commond Command provides functions can be done by a number of devices but not all.

Device Specific Command provides special instructions for each specific device.

Figure 7 lists the information can be obtained from the device on. The integration of HART is very tight because the state information is included in each of the core information and communication testing is done in a fast wizard continued. Each message can convey information related to 4 process variables and each device can handle 256 process variables.

Device Description Language (DDL) - Device Description Language, an improvement of HART technology in recent years have increased flexibility in the application of the device, shown in Figure 8. DDL provides equipment (slaver) capabilities allow the device to update the description with all the relevant information characteristics and thus can communicate with any Master that uses the same language. This helps to align the handheld devices (hand-held) can communicate with many devices of different vendors, just as long as you use the same language DDL.

The HART bring benefits?

The simplicity of the HART protocol has created favorable conditions for both manufacturers and users to get the experience and benefits of two-way communication capabilities of smart sensors using this technology. Ability to handle and much faster data transfer performance with remote capability, and error free detection devices, reduce the cost price, network installation serial capability, flexibility in configuration and change settings, digital signal processing is accurate nyh] NGX priority in Vietnam have been using the device HART technology. Also compatible with the 4-20 mA signal would make traditional investors to more easily upgrade the system while protecting previous investments in existing systems and can still be Vietnamese superiority of digital media technology.

Advantages of communication using HART technology has been proven through actual use in the cost of installation, commissioning, operation and maintenance. Devices using HART technology is widely used in various applications. From handling chemicals / petroleum, gas distribution systems, oil and the control station remote monitoring. Vietnam has shown the superiority in the data acquisition, supervisory control and maintenance. There were about 1.4 million works using this type of equipment. Below is a summary of the reasons for the success:

- With a large number is increasing constantly HART devices worldwide capacity, standard HART communication is "open" and is being standardized for industry. Users can freely choose the right product for your application and compatibility will always be guaranteed.

- Relatively easy to understand and use, HART provides access to a large amount of information in smart sensors, allowing HART devices can be equipped with more powerful tools such as algorithms PID control, self-blame, and features the new measure. And the communication between the devices nguou AVF is also very easy through the alignment of hand-held devices without affecting the normal operation of the device.

- HART technology solution without risk, for the operation and maintenance is very easy, all the worry about making sure to keep the system operating normally during maintenance is not required necessary because during the 4-20 mA signal remained constant, without removing / re-insert the device. In addition, two-way communication capabilities have contributed significantly to improving the operational efficiency of the plant.

- Finally, in case necessary and appropriate, using HART devices can be connected in serial configuration (Multidrop) to reduce the cost of installation.

In Vietnam, the technology for HART devices are widely used in industry, especially in the oil and gas sector, the common device is the Pressure Transmitter, Level Transmitter, Temperature Transmitter, Transmitter Density, Flow Transmitter ... Yokogawa (Japan), Emerson Process Managerment (American), the Flame / Gas / Smoke Detector Detronics of (American).

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