Meriam MFT 4010 Modular Calibrator_HART Communicator - Manual (Page 57)

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MFT 4010 with HART
®
Communications
Overview
The MFT 4010 includes HART communication functions that allow the user to poll, configure and maintain supported
HART field device. The MFT 4010 uses a combination of Universal, Common Practice and Device Specific
commands to facilitate communication with a field device. Combining HART ability with the modular calibrator means
that technicians can use one device to perform device analog output trim adjustments (4 and 20 mA), trim the sensor,
re-configure the field device, or poll a device for basic information.
The MFT 4010 will communicate with any HART device through Universal and Common Practice Commands using
the standard Generic DOF (Device Object File) but must have the DOF for a specific HART device installed before it
can execute Device Specific Commands. Consult the list of available DOFs at
www.meriam.com . Click on the
“Available DOFs” button for an up to date list of HART devices.
HART COMMANDS
Three HART command types are used by the MFT 4010 to communicate with HART field devices. First,
Universal Commands
are primarily used to identify a field device by its model number and tag number and to
read process data from the device. This communication is often referred to as “polling”. The MFT 4010 can poll
any Hart Device. Second, Common Practice Commands are used for calibration and maintenance functions
that are common to many devices. An example of this would be to trim or adjust the analog output. Third,
Device Specific Commands
are used to handle functions that are unique to a particular device or manufacturer.
Examples of these commands include sensor zero, sensor trim, calibration curve characterization, density
inputs required for calculations made by the HART device or other configuration functions unique to the specific
device.
HART CONNECTIONS
HART connections are made using the two standard banana jacks (3/4” center) located at the bottom of the
MFT 4010. Refer to the following diagram. Polarity is not a concern for HART connections so both jack collars
are black. Meriam supplies a test lead kit (P/N A36744) complete with standard connector for each model MFT
4010.
MFT 4010 with HART®
Electrical connections are shrouded standard banana jacks (3/4” center) for 50
mA/volts measurements. HART
® loop connections are also standard banana jacks.
Since HART is polarity independent, the HART jacks both have black collars.
For low load loops (less than 250 ohm), a 250 ohm resistor will need to be added to insure reliable HART
communications. Meriam supplies a 250 ohm load resistor in the form of a standard adaptor (P/N A36821).
Refer to the following diagram for details on connecting the adapter. This method requires the loop be opened
in order to make the necessary connections.