SMAR HI302, Руководство пользователя

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Installation
2.8
Maximum Cable Length
The user may choose from a shielded pair of twisted cables, a multi-pair of cables with a
single shield or a combination of these.
IMPORTANT
The shield can be overlooked if noise in the environment or any other interference do not
affect the communication.
Use a 24 AWG (0,5 mm) cable for lengths up to 5000 ft. For lengths in excess of 5000 ft
use at least a 20 AWG (0,8 mm) cable.
If a cable longer than 500 m is required, make a detailed analysis of the system to avoid
operation failures. According to HFC (HART Communication Foundation), the maximum
cable length depends on:
•
The cable’s resistance and capacitance,
•
The device’s resistance and capacitance on the HART channel, as well as the
additional equipment.
Due to the complexity of the subject, users should read the
HART Foundation
Communication
documentation, specially the
FSK Physical Layer
document.
Other devices in the Loop
The control loop may have additional devices, besides the HI302 and the HART devices.
See some common types as follow.
Portable Configurator
As we mentioned before, the HI302 operates as a master in most applications. So, there
is no problem in using a portable configurator, such as a HP301. Whatever the installation
topology, make sure to install a 25 Ohms impedance serial to the power supply. If no
active impedance or resistors are installed, the secondary master device will not
communicate.
Indicators and Converters in general
Indicators and converters are very common in industrial installations. They usually have
high impedance in the HART communication frequency (1200 to 2200 Hz). Sometimes
the introduction of such elements in the loop can prevent communication. However, there
is a simple and well known solution for this problem, by connecting a capacitor ranging
from 0.1 to 1
µ
F (100v at least) parallel to the device. This capacitor supplies an
impedance of hundreds Ohms parallel to the device’s impedance, allowing the HART
communication.
Switching On the HI302
When you turn on the module, the system will check some important hardware and
software components. If any errors are found, the module will not operate and the
FAILURE LED (red LED) will light..The HART LEDs (green LEDs) will blink slowly around
¼ Hertz. This check takes approximately 1 minute, so you should wait before checking
the HI302 in the Live List or watch for any value.