HART Fieldbus Flashcards
What does the acronym ‘HART’ stand for?
Highway Addressable Remote Transducer
What topologies are used with the HART protocol?
Point to point
Multi-drop
What topology(ies) can be used if a field device is configured to use simultaneous
analog/digital signaling?
Point to point topology
What topology(ies) can be used if a field device is configured to use digital-only signaling?
Multi-drop topology
If a HART field device has address 3, what type of signaling does this device use?
Digital signalling
If a HART field device has address 0, what type of signaling does this device use?
Simultaneous Analog/Digital
What is the data speed (in bps) for HART digital signaling?
1200 bps
What is the asynchronous frame structure for HART digital signaling?
8 Data Bits, Odd Parity, 1 Stop Bit
What cable types are recommended for HART wiring?
Shielded Twisted Pair
What address (or range of addresses) can be assigned to a HART field device to enable to use
simultaneous analog/digital signaling?
0
What address (or range of addresses) can be assigned to a HART field device to enable to use
digital-only signaling?
1-15
Calculate the maximum number of field devices that can be connected to a HART multi-drop
fieldbus network to limit the maximum current on the bus to 20mA
5
What Media Access method(s) is (are) used by HART?
Master/slave or burst mode
What connection topology must be used if Burst Mode is to be used?
Point-to-Point
What type of BCC character is used for HART digital signaling?
XOR checksum
What data does HART command code 2 request from a field device?
Reads PV in mA and as a percent of span
What SCADAPack ISaGRAF function block is used to read the PV (only) from a field device in engineering units?
hart1
For a point-to-point HART topology what is the minimum and the maximum loop resistance required?
230 to 1100 Ohms
What is the function of a secondary device in point-to-point HART topology?
Enables troubleshooting and device configuration
True/False. In a multi-drop system all devices have to be configured to digital ONLY signalling.
True. This is because the multi-drop system can host 3 or 4 devices and each device needs a unique address between 1 and 15.
What is an advantage of the multi-drop system over point-to-point?
Since only 1 pair of wires is required to run from control room to the field the wiring costs are much lower
What are the disadvantages of the multi-drop systems?
1) Slow update rate
2) No standard HART commands to write PV data to a valve positioner
3) The hardware in most controllers and HART multiplexers do not support multi-drop bus systems
4) No standard wiring devices available to make installations easier
Where can a multi-drop bus system be applied?
Applications that can safely tolerate slow response times such as tank level
