Fluid Components Intl ST51A - HART Operation; Process Data Operation; ST51 A;ST75 A;ST75 AV HART Process Data Organization; ST51 A;ST75 A;ST75 AV Process Variable Slots

OPERATION ST51A/ST75A/ST75AV Mass Flow Meters
36 Fluid Components International LLC
HART Operation
HART (Highway Addressable Remote Transducer) is a communication protocol that superimposes a low level digital data signal on a 4-20 mA
current loop. The primary function of the instrument’s HART interface is to present process data via process data commands 1, 3 and 9.
The ST51A/ST75A/ST75AV does not implement the HART Burst mode. A HART master that supports HART 7.0 and higher is required. If
using a HART communicator, a unit that supports HART 7.0 or higher is required (i.e. Emerson 475 Communicator). Connect the
installation (factory/plant) HART wiring to the instrument as described in HART Connection, page 22.
Process Data Operation
The ST51A/ST75A/ST75AV implements HART 7.0 while maintaining compatibility with earlier versions of the HART protocol. However,
HART commands 1 and 3 have been simplified to only report the primary variable Flow. Use command 9 to access the full suite of
available dynamic variables including temperature, totalizer, and others.
ST51A/ST75A/ST75AV HART Process Data Organization
This section describes how the instrument process data is organized under the HART command 9. For details on command 9 see the
HART Specification “Universal Commands Specification” HCF_SPEC-127, Revision 7.1 and the command 9 description on page 42.
ST51A/ST75A/ST75AV Process Variable Slots
Table 10 below lists the instrument’s 6 process variables that are read by HART command 9, with each process variable assigned a slot number.
Not all the variables described in this section are available in all configurations of the flow meter. For example, the Flow Totalizer may be
turned ON or OFF.
The process variables include 3 flow classes or types of which only one class of flow is active at a time.
Table 10 – ST51A/ST75A/ST75AV HART Process Variables
Slot #
Process Variable
HART Variable Code
Description
Device Variable Code
Device Variable
Classification
0
Volumetric Flow
1
Primary Variable
0
66
1
Volume (Totalizer)
Secondary Variable
1
68
2
Mass Flow
1
Primary Variable
2
72
3
Mass (Totalizer)
Secondary Variable
3
71
4
Velocity Flow
1
Primary Variable
4
67
5
Temperature
Tertiary Variable
5
64
Note: 1. Only one flow variable active at a time.
Primary Variable Classifications
The instrument can provide flow data in unit types that span several HART classifications. Commands 50 and 51 are used to read and set,
respectively, which flow variable will be mapped to the primary variable. The PV device variable classification can only be one of the following:
● 0: Volumetric Flow
● 2: Mass Flow
● 4: Velocity Flow
Since only PV is used in this manner, command 50 returns 250 for SV, TV, and QV. The setting of the device variable classification determines
which class of flow-related variables is valid, and therefore displayed as implemented when variable slots are read by command 9.
Device Description Files
A Device Description (DD) file lets the HART handheld or host software application fully configure any HART device for which it has a DD
installed. The ST51A/ST75A/ST75AV DD files are available for download from the FieldComm Group website:
https://fieldcommgroup.org/registered-products/
Search by Manufacturer (Fluid Components International LLC) to find the instrument’s files under the product name: FCI ST51A/ST75A
Series. The posted DD files are contained in a zip archive with FCI’s manufacturer ID and product device type hex values embedded in the
filename (e.g., hart.0000a6.a67e.zip).