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COMMON ANALOGUE GROUNDING ISSUES
Correctly connecting the Intellivox to ground has several
benefits:
1. Safety. The GND terminal of the IEC mains connector
provides a direct low impedance path from the
metal parts of the chassis to ground. Always
connect this terminal.
2. Reduction of RF emission. Although the Intellivox
electronics module is well shielded and external
connections are decoupled to prevent RF emission from
the internal high speed digital circuits, this protection
will not work properly if the chassis is not connected to
ground.
3. RF Immunity. RF currents induced in the signal cables by
external RF fields are effectively shorted to chassis-
ground, provided that the cable screen (shield) is of
sufficiently low impedance.
In addition to the mains ground, the Intellivox connector
block has ground pins marked in 3 different ways. Each
serves a dedicated purpose and care should be taken that
they are not interchanged or connected to each other.
• Pins marked GND are connected internally directly to
the chassis of the Intellivox. There are GND pins on the
audio line input connector and the ambient SPL
mic/temperature sensor connector. These GND pins are
for connecting the screen (shield) of the audio and
sensor cables.
• Two pins marked AGND are fitted to the ambient SPL
mic and temperature sensor connector, and serve as a
signal reference only. AGND should not be connected
to any other ground pin (GND or DGND) on the chassis.
• The RS-485 connector has one pin marked DGND and is
intended as a terminal for the network cable screen
(shield). Since the RS-485 interface is optically isolated
(to prevent ground loops), DGND has no relation to the
chassis ground. DGND should not be connected to any
other ground pin (GND or AGND) on the chassis.
24
SOFTWARE AND FIRMWARE UPDATES
The WinControl application is freely available and can be
downloaded from the download area of our website;
http://www.jblpro.com. We advise installers, users and
engineers to check our site regularly for updates. Intellivox
firmware and DSP software upgrades will also be made
available through the website.
For further information about how to use WinControl please
refer to the WinControl Help files.
NETWORK CABLES
The type of cable necessary for correct operation of the
RS-485 network is twin twisted pair with each pair individually
shielded. Numerous cables of this type are readily available
and cables broadly meeting the specifications of the
example cable given below are likely to be suitable.
Example of a preferred cable type:
PARAMETER
Type
Characteristic impedance
Capacitance (core to core)
Capacitance (core to screen)
DC resistance (core)
DC resistance (screen)
JBL Intellivox Installation Manual
VALUE
BELDEN 'Datalene' series
No. 9729 2-pair
100 ohms
41 pF/m
72.5 pF/m
78.7 ohms/km
59.1 ohms/km
201401/IvxIM_v2.2
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