HART Protocol With Reference To OSI Model

HART protocol

The HART (Highway Addressable Remote Transducer) Communication Protocol directly contributes to these business goals by providing cost savings in:

Commissioning and installation
Plant operations and improved quality
Maintenance

Products that use the HART protocol to provide both analog 4-20A and signals provide flexibility not available with any other communication technology.

The HART Communication Protocol is based on the Bell 202 telephone communication standard and operates using the frequency shift keying (FSK) principle.

The digital signal is made up of two frequencies: 1,200 Hz and 2,200Hz representing bits 1 and 0, respectively.

Sine waves of these two frequencies are superimposed on the direct current (dc) analog signal cables to provide simultaneous analog and digital communications. Because the average value of the FSK signal is always zero, the 4-20mA analog signal is not affected.

HART Data

Digital data

35-40 valuable data items standard in every HART device

Device identification

Device tag, suppliers, device type and revision, device serial number

Calibration data

Upper and lower range values, Upper and lower sensor limit, PV damping, last calibration date.

Process Variables

Primary variable plus secondary measurements and multivariable parameter.

Status/Diagnostic alerts

Device malfunction, configuration change, power fail restart, loop current fixed or saturated, primary and secondary variable out of limits, communication error