What is HART™ Communication Protocol and what are the benefits of HART when buying an SPX or Vertex sensor? Developed in the mid-1980’s, HART is an acronym for Highway Addressable Remote Transducer, and it enabled users to communicate over legacy 4-20 mA analog instrumentation. The benefits of choosing HART are Digital Capability, Analog Capability, Interoperability, & Availability.
Digital Capability allows access to all instrument parameters and diagnostics. Two common instrument parameters accessed are Upper Range Value (URV) and Lower Range Value (LRV). These values can be adjusted via HART handheld device to reflect accurate pressure reading at 4 mA. Example: if there is a 15 psig shift during start-up, a user can adjust the LRV so at 15 psig, the output will be 4 mA and span isn’t affected. It also allows the user to ‘turn down’ the pressure range. If a user has a 0-5000 psig sensor, they can adjust or turn down the URV to get closer to the actual pressure that the sensor will be seeing (more to follow on accuracy). It also allows for diagnostics of the sensors via failsafe conditions, which alert users that there could be a potential problem (see HART portion of SPX user manual for additional details).
As mentioned earlier, a HART device can enable a user to adjust pressure output ranges. When that is done, the published accuracy of the sensor is affected. Most of our SPX series sensors have a 5:1 turndown ratio; which means that a 0 – 5000 psig sensor can be turned down so at 0 psig, the output will read 4 mA (perfect world) and at 1000 psig, the output will read 20 mA. However, the accuracy will increase by a multiple of 5. Our SPX2242 series sensor has an FSO of 0.25% when operating at full scale (0-5000 psig). If the sensor was to be turned down to 0-1000 psig, the accuracy/resolution would be 1.25%.
For additional information on HART, please contact your Regional Sales Manager
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