PHYSICAL CONNECTION OF HART DEVICES & NETWORKS
HART signal is modulated by varying the loop current or by directly modulating a voltage onto the loop. Process transmitters vary the loop
Current 0.5 mA. For each type, the specification establishes signaling levels, device impedances, and internal filter requirements.
Current 0.5 mA. For each type, the specification establishes signaling levels, device impedances, and internal filter requirements.
DEVICE DESCRIPTIONS
Section demonstrates, considerable functionality is available using the standard HART commands that all field devices support. While these commands address routine, continuous systems requirements like acquisition of cyclical process data and online status and diagnostic monitoring, from time to time device-specific features and configuration properties must be accessed. Device descriptions (DDs) facilitate access to the occasionally needed device-specific features.
The Device Description Language (DDL) is a very powerful technology that provides significant benefits for the configuration and setup of device-specific features. Although DDs are an optional part of the HART protocol, most HART-compatible devices have a corresponding DD registered with the HCF.
The DDL is an object-oriented modeling language tailored to describing field devices, and DDs do this very well. DDL consists of three major functional areas:
1. Modeling the field device application layer data
2. Describing the commands used to transport that data
The Device Description Language (DDL) is a very powerful technology that provides significant benefits for the configuration and setup of device-specific features. Although DDs are an optional part of the HART protocol, most HART-compatible devices have a corresponding DD registered with the HCF.
The DDL is an object-oriented modeling language tailored to describing field devices, and DDs do this very well. DDL consists of three major functional areas:
1. Modeling the field device application layer data
2. Describing the commands used to transport that data
3. Specifying the standard operating procedures (SOPs) used for periodic maintenance.
CALIBRATING HART FIELD DEVICES
All field devices, regardless of the communications protocol they support, need periodic calibration. Calibration of HART devices includes calibrating the digital process value, scaling the process value into a percent of range, and transmitting it on the 4–20 mA current loop. HART devices use standardized commands to test and calibrate the loop current, re-range a field device, and even perform a
transducer trim.
A block diagram showing the processing steps associated with generating PV and will be used to illustrate the calibration process. Three blocks are used for data acquisition and communication of PV via the current loop. From left to right, these blocks include:
1. The Transducer block
2. Range block
3. DAQ block
transducer trim.
A block diagram showing the processing steps associated with generating PV and will be used to illustrate the calibration process. Three blocks are used for data acquisition and communication of PV via the current loop. From left to right, these blocks include:
1. The Transducer block
2. Range block
3. DAQ block
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