HART is a digital device, so this digital signal will superimpose on the analog transmiiter signal without disturbing it.
Post New Answer. An atmospheric storage tank has a diameter of 20 m and a height of 8m. It is half-full of liquid with the remainder of the space containing air normally at atmospheric pressure. If the connection to atmosphere is accidentally closed off and 10 cubic m of liquid removed, what happens to the internal pressure of the tank?
What are the possible consequences for the tank? Common Practice: This set of commands provides functions implemented by many - but not necessarily all - HART communication devices. Device Specific: Device specific commands represent functions unique to each device.
These commands access configuration and calibration information, as well as information about device construction. Information about Device Specific commands is available from device manufacturers. Among these features, we can point out the easy identification and verification of each HART device, easy verification of loop integrity and maintenance of device records as installed.
Less time spent in device commissioning results in cost savings. Before installation, a tag is usually inserted, along with other identification data and the configuration of each instrument going to the field. This information is usually provided when the device is requested by the master. After installation, the instrument identification, tag and descriptor can be easy verified by using a device configurator, which can be a handheld communicator or a PC using a modem connected to the device or the 4- 20 mA loop.
Some field devices provide information about their physical configuration. For example, devices can handle wet materials, ratings, or boundaries of different types. Physical data and other configuration data can be verified in the control room. The verification process is important for safety and in compliance with governmental regulations and ISO quality requirements.
The commissioning process can be further simplified by connecting a PC-based configuration application to each HART loop. With this centralized approach, there is no need to move the device from one endpoint configuration to the next during the commissioning of all devices on the network.
Once a field instrument has been identified and its configuration data confirmed, the integrity of the analog circuit can be verified using the loop test feature, supported by many HART-enabled devices. The loop test allows the analog signal of a HART transmitter to be set to a specific value.
This fixed value checks the integrity of the loop and ensures a proper physical connection between all network devices. Additional integrity can be obtained if the analog value is compared to the digital value reported on a device.
For example, something may have entered an offset to the analog value of 4 to 20 mA that was not counted in the control system. By comparing the digital value of the primary variable with the analog value, the integrity of the loop can be checked. Many HART configurators also keep records of device configuration data, so they can be restored for archiving or printing. In case of device replacement, this ensures configuration recovery, while facilitating record-keeping compliance.
This can be done using a permanent or temporary physical connection. The connection does not need to be at the device terminals. This feature can reduce the number of field trips, since the access can be made in the relay or termination panel. Among the many reasons to communicate with a specific device we can list:.
Some control and monitoring systems provide configuration resources for permanently connected devices. In order to configure a HART-enabled device using a temporary connection, you can use either a universal handheld configuration tool or a PC running a device configuration application and a HART modem.
For both cases, a power supply and a load resistor are also needed. They are available from suppliers around the world and are supported by FieldComm Group. However, on this case, extra or device specific commands will not be accessed, which can lead to a limited experience.
There are between 35 and 40 standard data items on all registered HART devices. Data can be accessed by any communicator or approved configuration tool. These items do not require a DD and usually include the basic functionality of the device. Accessing device specific data requires a current DD for that particular device as it provides the communicator with the information needed to fully access all of the device's specific features.
If equipped, a HART handheld communicator can also make it easier to maintain device configuration records. The configuration data of the installed device can be stored in memory or on a disk for later archiving or printing. A multi-meter can also be inserted in the loop as an additional checks. This loop check method also does not require a person to go to the field.
However, there is no indication if the valve is actually moving. You can also follow us on Facebook and Twitter to receive daily updates. Field Instrumentation Tips. Process Interlocks and Trips. Fieldbus Split Range Valves. Transmitter mA Limits. Recommended Articles. Very useful info sir. Salute u. Very Good web site i like that Reply.
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