System integration iTEMP TMT162
30 Endress+Hauser
7.2 Device variables and measured values
The following measured values are assigned to the individual device variables:
Device variable code Measured value
0 Sensor 1
1 Sensor 2
2 Device temperature
3 Average of sensor 1 and sensor 2
4 Difference between sensor 1 and sensor 2
5 Sensor 1 (backup sensor 2)
6 Sensor 1 with switchover to sensor 2 if a limit value is exceeded
7 Average of sensor 1 and sensor 2 with backup
The device variables can be queried by a HART
®
master using HART
®
command 9 or
33.
7.3
Supported HART
®
commands
The HART
®
protocol enables the transfer of measuring data and device data between
the HART
®
master and the field device for configuration and diagnostics purposes.
HART
®
masters such as the handheld terminal or PC-based operating programs (e.g.
FieldCare) need device description files (DD, DTM) which are used to access all the
information in a HART
®
device. This information is transmitted exclusively via
"commands".
There are three different types of command
•
Universal commands:
All HART
®
devices support and use universal commands. These are associated with the
following functionalities for example:
– Recognition of HART
®
devices
– Reading digital measured values
• Common practice commands:
Common practice commands offer functions which are supported and can be executed by
many but not all field devices.
• Device-specific commands:
These commands allow access to device-specific functions which are not HART
®
standard. Such commands access individual field device information, among other
things.
Command No. Designation
Universal commands
0, Cmd0 Read unique identifier
1, Cmd001 Read primary variable
2, Cmd002 Read loop current and percent of range
3, Cmd003 Read dynamic variables and loop current
6, Cmd006 Write polling address
7, Cmd007 Read loop configuration
8, Cmd008 Read dynamic variable classifications
9, Cmd009 Read device variables with status
11, Cmd011 Read unique identifier associated with TAG
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