Reference Manual

00809-0100-4697, Rev EA October 2011

Rosemount 848T

DEVICE DESCRIPTIONS

BLOCK OPERATION

Instrument- Specific Function Blocks

Alerts

Device Descriptions (DD) are specified tool definitions that are associated with the Resource and Transducer Blocks. Device descriptions provide the definition and description of the function blocks and their parameters.

To promote consistency of definition and understanding, descriptive information, such as data type and length, is maintained in the device description. Device Descriptions are written using an open language called the Device Description Language (DDL). Parameter transfers between function blocks can be easily verified because all parameters are described using the same language. Once written, the device description can be stored on an external medium, such as a CD-ROM or diskette. Users can then read the device description from the external medium. The use of an open language in the device description permits interoperability of function blocks within devices from various vendors. Additionally, human interface devices, such as operator consoles and computers, do not have to be programmed specifically for each type of device on the bus. Instead their displays and interactions with devices are driven from the device descriptions.

Device descriptions may also include a set of processing routines called methods. Methods provide a procedure for accessing and manipulating parameters within a device.

In addition to function blocks, fieldbus devices contain two other block types to support the function blocks. These are the resource block and the transducer block.

Resource Blocks

Resource blocks contain the hardware–specific characteristics associated with a device; they have no input or output parameters. The algorithm within a resource block monitors and controls the general operation of the physical device hardware. The execution of this algorithm is dependent on the characteristics of the physical device, as defined by the manufacturer. As a result, the algorithm may cause the generation of events. There is only one resource block defined for a device. For example, when the mode of a resource block is “Out of Service (OOS),” it impacts all of the other blocks.

Transducer Blocks

Transducer blocks connect function blocks to local input/output functions. They read sensor hardware and write to effector (actuator) hardware. This permits the transducer block to execute as frequently as necessary to obtain good data from sensors and ensure proper writes to the actuator without burdening the function blocks that use the data. The transducer block also isolates the function block from the vendor–specific characteristics of the physical I/O.

When an alert occurs, execution control sends an event notification and waits a specified period of time for an acknowledgment to be received. This occurs even if the condition that caused the alert no longer exists. If the acknowledgment is not received within the pre-specified time-out period, the event notification is retransmitted, assuring that alert messages are not lost.

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Emerson 848T manual Device Descriptions Block Operation, Instrument- Specific Function Blocks Alerts, Resource Blocks

848T specifications

The Emerson 848T is a state-of-the-art temperature transmitter designed for accurate and reliable temperature measurement in various industrial applications. This device has gained recognition for its advanced features and robust performance, making it a popular choice among engineers and technicians in the field.

One of the key highlights of the Emerson 848T is its unique dual-channel capability, which allows it to seamlessly monitor two temperature sources simultaneously. This functionality is particularly beneficial in processes where multiple temperature points need to be assessed, optimizing efficiency and reducing the need for additional equipment. It supports various sensor types, including thermocouples, RTDs, and resistance temperature detectors, making it versatile for different applications.

The 848T is equipped with sophisticated digital processing technology, which enhances its accuracy and stability. It features a 24-bit analog-to-digital converter, ensuring precise measurement and minimizing drift over time. Moreover, the device boasts a wide operating temperature range, accommodating ambient conditions from -40°C to 85°C. This durability makes it suitable for harsh environments commonly encountered in industries such as oil and gas, pharmaceuticals, and power generation.

Another significant characteristic of the Emerson 848T is its configurable output options. Users can choose from a range of output signals, including 4-20 mA, which provides a standard interface for integration into existing control systems. Additionally, it offers a HART communication protocol, allowing for easy configuration, calibration, and diagnostics through a digital interface. This feature enhances the transmitter's usability, enabling operators to perform adjustments without direct access to the device.

The device is designed with user-friendliness in mind. Its intuitive setup procedure and robust graphical user interface simplify the commissioning process, ensuring that even those new to the technology can easily navigate the system. An integrated LCD display provides real-time readings and status information, facilitating monitoring at a glance.

In summary, the Emerson 848T temperature transmitter combines reliable performance, user-friendly design, and advanced digital technologies. Its dual-channel capability, wide sensor compatibility, and adjustable output options make it an essential tool for achieving precise temperature measurements in various industrial settings. With these compelling features, the Emerson 848T stands out as a leading choice for professionals seeking accuracy and efficiency in their temperature monitoring applications.