CIRCUTOR CVMk2 Series - Manual (Page 143)

143
CVM k2
OPERA
TION
143
CVM k2
COMMUNICA
TION
9 . MAINTENANCE AND CALIBRATION
CVMk2 does not require maintenance work since it is a completely static instrument.
Nonetheless, it is recommended to verify that the terminals are properly tightened.
9.1 MAINTENANCE
To increase the system's capacity with expansion cards before handling, modify
its connections or replace equipment; CVMk2 must be power OFF.
Handling the system while it is powered up is dangerous for the persons and the
equipment.
The RS-485 connection is made with screened but flexible twisted pair communication cable
with a minimum of three wires. Maximum distance between the master and the last peripheral
device is 1.200 metres.
For RS-485 connection over longer distances or where there are hi level of disturbances
environment, twisted screened cable should always be used.
RECOMMENDED CABLE
Flexible category 5 cable, 4 conductors x 0.5 mm 2 (AWG 20) shield. The shield should be
connected to ground in order to discharge noise that it may be induce. This cable can also use
conductors with 0.22 mm 2 cross sections (AWG 24), although the 0.25 mm 2 or higher, (AWG
23) is recommended.
No. OF PERIPHERAL DEVICES:
A maximum of 32 peripheral devices can be connected to the network, and amplifiers can be
used to extend the bus 1.200 additional metres.
Other considerations:
● Install the RS-485 BUS far away from electrical power lines.
● In facilities with long distances of RS-485 BUS, it is recommended to install components
to protect against overvoltages in the BUS (voltages induced in the BUS by atmospheric
discharges or ground potential differences).
● Do not make a star connection for the RS-485 BUS; i.e., do not make branches off the
bus. The connection between a group of 485 peripherals and the BUS should be as short
as possible.
● The analyzers GND should not be connected in the 485 BUS, i.e. system GNDs should
not be connected one to another in order to avoid currents circulating between grounds
at different potentials.
● The systems GND should neither be connected to the cable screen nor to the facility's
ground.
8.4. RS-485 NETWORK FEATURES