What is the difference between 4 20mA and HART?
What is the Difference Between 4 20mA and HART?
Difference Between 4 20mA and HART Communication
4 20mA and HART are both quite popular in industrial instruments but serve very different roles in process control systems. They are vital to know for troubleshooting, calibration and smart integration of the instruments.
The 4 20mA signal is a popular analog communication protocol that is used to send a single process variable such as pressure, flow, level or temperature. In this system, the minimum value is 4mA and the maximum measurement range is 20mA.
HART is a digital communication system that is layered on the 4 20mA analog signal. This allows for additional device information to be provided without compromising the analog measurement signal.
Main Differences
- 4 20mA carries only single analog process value
- HART transmits both analogue and digital data
- 4 20mA is generally used for basic process control.
- HART provides diagnostics and remote configuration
- 4 20mA manual calibration tests
- HART allows online calibration and device monitoring
- HART provides sensor status, tag information and fault alerts
Real Plant Scenario
Many functioning plants still use 4 20mA loops of outdated transmitters to provide a stable signal. Modern smart transmitters are HART communicating to facilitate sophisticated diagnostics and predictive maintenance yet backward compatible with existing control systems.
HART enhances diagnostics and visibility of devices for instrumentation professionals. 4 20mA still very dependable for simple process measurement and control applications in severe industrial environments.