Hart Variables - Siemens SIMATIC ET 200SP Manual

HART function

4.4 HART variables

4.4 HART variables
Introduction
Numerous HART field devices make available additional measured quantities (e.g. sensor
temperature).
A maximum of four HART variables supported by the connected field device can be cyclically
read per channel with activated HART functionality. The HART variables are read automatically
with HART command 3 (for field devices with HART rev. 5 and 6) or with command 9 (for field
devices with HART rev. 7 or later).
These four HART variables per channel are always stored in HART variable data record 121
and can be read at any time. See section HART variable data record (Page 58).
In addition, a maximum of 4 HART variables can be configured directly in the input address
space of the AQ 4xI HART analog module. The HART variables are assigned to a channel in
the properties dialog of the module. The parameter assignment uses parameter data record
140, see section Parameter assignment and structure of the HART mapping parameters
(Page 55). This allows you to easily work with process values directly from the field device as
input data in the automation device.
Address assignment
Provided you map HART variables in the input address space of the module by means of the
configuration tool or selection of the appropriate configuration, 20 bytes are always additionally
allocated for the HART variables.
Configuration of HART variables
You can configure up to 4 HART variables for each channel. When configuring, you select
these from the four HART variables provided by each channel:
● PV (Primary Variable)
● SV (Secondary Variable)
● TV (Tertiary Variable)
● QV (Quaternary Variable)
When HART mode is enabled, the analog module cyclically reads the variables provided by the
connected field devices independently and makes them available in the configured input
address space. You specify during parameter assignment which variables are supplied by a
field device.
Each HART variable consists of a 4-byte value and a quality code byte.
Quality code
The quality code describes the process status of the corresponding HART variable.
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Analog Output Module AQ 4xI HART HF
Manual, 05/2019, A5E35098013-AA