Rosemount Model 1195/ProPlate/Mass ProPlate
5-22
Burst Mode
When configured for burst mode, the ProPlate provides faster digital
communication from the flowmeter to the control system by eliminating
the time required for the control system to request information from
the flowmeter. Burst mode is compatible with use of the analog signal.
Because HART protocol features simultaneous digital and analog data
transmission, the analog value can drive other equipment in the loop
while the control system is receiving the digital information. Burst
mode applies only to the transmission of dynamic data (pressure and
temperature in engineering units, pressure in percent of range, and/or
analog output), and does not affect the way other flowmeter data is
accessed.
Access to information other than dynamic flowmeter data is obtained
through the normal poll/response method of HART communication. A
HART-based communicator or the control system may request any of
the information that is normally available while the flowmeter is in
burst mode. Between each message sent by the flowmeter, a short
pause allows the HART-based communicator or a control system to
initiate a request. The flowmeter will receive the request, process the
response message, and then continue “bursting” the data
approximately three times per second.
Multidrop Communication
Multidropping transmitters refers to the connection of several
transmitters to a single communications transmission line.
Communication between the host and the flowmeters takes place
digitally with the analog output of the flowmeters deactivated. With the
HART smart communications protocol, up to 15 transmitters can be
connected on a single twisted pair of wires or over leased phone lines.
This feature can greatly reduce wiring costs.
The application of a multidrop installation requires consideration of the
update rate necessary from each transmitter, the combination of
transmitter models, and the length of the transmission line. Multidrop
installations are not recommended where intrinsic safety is a
requirement. Communication with the transmitters can be
accomplished with commercially available Bell 202 modems and a host
implementing the HART protocol. Each transmitter is identified by a
unique address (1–15) and responds to the commands defined in the
HART protocol. HART-based communicators can test, configure, and
format a multidropped flowmeter the same way as a transmitter in a
standard point-to-point installation.
Figure 5-8 on page -23 shows a typical multidrop network. This figure
is not intended as an installation diagram. Contact Dieterich Standard
product support with specific requirements for multidrop applications.
HART Comm. 1, 4, 3, 3, 3
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