Detcon FP-524D-HRT - Manual (Page 30)

Model FP-524D-HRT
FP-524D-HRT Instruction Manual Rev. 0.1 Page 26 of 48
4. HRT Bridge
The HRT Bridge interface is an integral part of the Transmitter Module for the FP-524D-HRT. The sensor
utilizes the a 4-20mA output with the added HART interface information.
4.1 Description
The HRT Bridge PCA is a bi-directional digital communication interface that provides data communication
between the Model FP524D-HRT sensor and HART
® -enabled devices. The HART ® (Highway Addressable
Remote Transducer) Communication Protocol is a standard for sending and receiving digital information
across analog wires between smart devices and a control host or monitoring system. A host can be any
software application from a technician's hand-held device or laptop to a plant's process control, asset
management, safety or other system using any control platform.
The HART Communication Protocol makes use of the Bell 202 Frequency Shift Keying (FSK) Standard to
superimpose digital communication signals on the 4-20mA signal utilized by the FP-524D-HRT sensor. This
enables two-way communication and makes it possible for additional information to be transferred to and from
the sensor. This communication includes the ability for the Host to:
 Configure or re-configure the sensor
 Perform sensor diagnostics
 Troubleshoot the sensor
 Read additional information from the sensor
 Determine the sensor’s health and status
4.2 Connecting the HRT Bridge
The HRT Bridge connection to the Host utilizes the same 3-wire connection of power, power return, and mA
output as the typical FP-524D (Refer to Figure 8 Base Connector Board). Connect the 24VDC to the base
connector board terminal labeled ‘DC+’. Connect the 24V Return to the terminal labeled ‘DC-’, and connect
the 4-20mA to the terminal labeled ‘mA’. The 4-20mA signal from the HRT Bridge must be connected to a
load resistor to operate properly. If this signal is not terminated properly, the HRT Bridge, and the HART
Interface will fail to work properly.
4.3 Operation
When power is applied to the FP-524D with HRT Bridge, the HRT Bridge will go through a boot up sequence
that will last for approximately 30 seconds. During this time, the 4-20mA line will be held at 1mA. After the
boot up sequence the HRT Bridge will enter normal operation, and communication with the Host will begin.
A red LED (D7) Labeled “HART” on the HRT Bridge PCA will illuminate when the PCA is communicating
with the HART Host. (The HRT Bridge is part of the FP-524D-HRT Transmitter assembly.)
The 4-20mA signal from the HRT Bridge must be connected to a load resistor for HART communication to
operate properly. If this signal is not terminated properly, the HRT Bridge, and the HART Interface will fail to
work. Normal termination for the 4-20mA signal is accomplished by connection to a Host device, which will
have the correct load to terminate the signal properly.
If the HRT Bridge senses a fault in the sensor, it will take the 4-20mA signal down to 1mA. This 1mA signal
will signify to the Host that a sensor fault has occurred, and the Host should, in turn, flag an error with the
associated sensor.