Overview
Theory of Operation
Theory of
Operation
HART Board
The HART board serves as an intelligent pass-through between the
“external” HART world and the gauge. It has three responsibilities:
● Maintain a local copy of all gauge setup data for fast retrieval.
● Offer real-time access to the gauge’s process and alarm data.
● Translate incoming HART requests to the equivalent native gauge
requests, collect the data, and send the response to the HART
requestor.
On the gauge side, the HART board co-opts the gauge’s RS232 port and
talks to it in logic levels in the usual ASYNC format. On the HART side,
the HART telemetry is “mixed” with the gauge’s 4–20 mA current out.
The HART master (usually the 275/375/later field communicator) talks to
the gauge over its current loop.
LevelPRO DD The LevelPRO DD is designed to offer access to the gauge’s process data
and basic setup functions, including:
● Primary measurement setup
● Process alarms
● Additional measurements
● Current output settings
● Gauge fine tuning
● Action items (gauge restart, erase memory)
As practical, the DD menu structure mirrors that found in the gauge. The
DD menu flowcharts appear in Appendix A.
Gauge Once the HART board is installed, the gauge enters a special mode of
operation by:
● Overriding all user RS232 selections and setting the port to 96007E1,
Blind Mode, data streaming inhibited.
● Disabling all RS232 setup menus in the gauge user system.
● Enabling HART board software watchdog, which monitors HART
board data requests. The watchdog will raise a system fault alarm if
there were no requests received in a one-minute interval.
1-2 LevelPRO HART Operation Guide Thermo Fisher Scientific