calibrating and trimming instruments via hart agenda: what is hart? / history / signal / message...
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Calibrating and Trimming Instruments via HART
Agenda:• What is HART? / History / Signal / Message Frame• HART Command Structure• Connecting a HART Transmitter• Trimming Devices• Trimming Conventional Transmitter vs. HART Transmitter• Live Demo
What is HART?
HART = Highway Addressable Remote Transducer
A digital communication protocol designed for industrial process measurement applications.
Uses a low-level modulation (FSK) superimposed on the standard 4 to 20 mA current
HART History
Revision Year2.0 19873.0 19884.0 19895.x 1989 – still delivered today6.0 2001 – never introduced7.0 2007 – introduction of HART
wireless
HART Signal
HART Message Frame
HART Command Structure Three levels of commands• Universal commands• Common practise commands• Device Specific commands
Universal commands•Model ID•Tag ID•Description•Message•Date•Range Values•Instrument Limits•Process Measurements•Device Status
Common practice commands•Read Variables•Calibration (zero, span)•Initiate Self Tests•Serial Number•Time Constant Values
Device Specific commands•Model Specific Functions•Start, Stop, or Clear Totalizer•Select Primary Variable•Special Calibration Options•PID - SP, Tuning, Etc.
Connecting a HART TransmitterPoint-to-point
24V supply
+
_
ResistorTransmitter
HART Communicator
mA
mA
Polling address = 0 !=> HART + mA signal
HART
Connecting a HART transmitterMultidrop
24V supply
+
_
Resistor
Transmitters (max 15 pcs), fixed 4 mA current,Only PV output, different addresses (not 0 !)
HART Communicator
4 mA (fixed)
...
Addr=1 2 15
Trimming Devices
Communicators Smart Calibrators
MC5 Internal Connections
24V supply
+
_
ResistorTransmitter
HART Communicator
mA
mA
MC5
+24V
Ground
HART
HART vs. Conventional Transmitter (1of 2)
Conventional transmitter
Input 4 … 20 mA
Adjustments:• Zero• Span
HART vs. Conventional Transmitter (2 of 2)
HART transmitter
Input 4 .. 20 mA
Digital trim Analog trim
RangeTransfer Function
PV
PV
Input section Output sectionConversion
AO
AO
A/D D/A
Live Demo
Presented by:Ned Espy – Consulting DirectorBeamex, Inc.Office: 770-951-1927Mobile: [email protected]