SMAR HI302, Руководство пользователя

Страница: 15 / 92

HI302 - User’s Manual
2.5
These concepts are of fundamental importance when connecting different devices. For
example, in the connection shown below, depending on the internal actuator impedance, it
may be necessary to install a resistor in series with the power supply. This is done to
achieve the minimum impedance requirement (25
Ω ).
IMPORTANT
Whatever the topology used, it is important to keep a 25 Ω impedance. In the previous
picture, it is not necessary to connect an impedance in series with the power supply if
the impedance read by the HART channel is at least 25
Ω . In case the impedance is
lower than 25 Ω , improve its value to the minimum requirement. The connection above
allows the communication between the two devices.
HART Installation Topology
The HI302 comply with several applications, since the new ones to older installations,
where it is necessary to increase the HART device’s life span and preserve the
investment with the gradual introduction of the Foundation Fieldbus technology. Below are
some examples of connections. However, the applications are not limited to these
examples and should be considered separately.
Supply Voltage X Total Loop Impedance
The total impedance of the devices connected to a pair of cables and the cable
impedance should be between the operation limits complying with the loop supply voltage.
See the next graphic: