A1 mains input and fuses
REMOTE
CONTROL
FUSE T2A
220V-240V
∼
50-60 Hz
OVER
VOLTAGE
FUSE T8A
FAIL
FAIL
(4.0 E)
2-3
2.1.5. Mains overvoltage protection
To protect against mains overvoltage damage the A1 is fitted with
an efficient, self-resetting mains overvoltage protection circuit.
As soon as the mains supply voltage exceeds 265 V (115 V for the
100 V supply version) the overvoltage protection circuit responds
and isolates the mainframe power supply from the mains supply
leaving only a supervisory circuit active to monitor the mains sup-
ply voltage. The green POWER LED on the mainframe front panel
goes out and the OVER VOLTAGE LED on the mainframe rear pa-
nel comes on.
Only if the mains voltage drops below 255 V (111 V) is the mai-
nframe automatically reconnected to the mains supply and normal
operation resumed. This 10 V difference in the protection circuit
switching levels (switching hysteresis) prevents the mainframe from
cycling on and off with a fluctuating mains supply voltage.
The protection circuit will operate with any mains overvoltage up
to 400 V; allowing the A1 to survive connection across two phases
of a three phase supply.
2.1.6. Mains inrush current limiter
The mains inrush current limiter ensures a slow "start-up" for the
mainframe and allows several mainframes connected to the same
mains supply circuit to be switched on together without temporarily
overloading the supply circuit and causing a breaker to trip. The
inrush current at switch on is limited to 5 A (230 V version).
Note that repeatedly and rapidly switching a mainframe on and
off will overheat and stress the inrush current limiter circuit - a rear
panel fuse protects the circuit from damage.
2.1.7. Fuses
Two 20 mm delay fuses are fitted on the mainframe rear panel -
an 8 A fuse for the mainframe power supply and a 2 A fuse pro-
tecting the mains inrush current limiter. If either fuse should blow
then the red LED (FAIL) indicator next to the respective fuseholder
will light.
2.1.8. Remote control & monitoring
The A1 is fitted with a twin wire remote interface for various levels
of remote control and system supervision of the mainframe and its
controller module. The remote interface connection is opto-isolated
and floating.
Basic Remote
The Basic Remote is the simplest way to implement a remote control
system. A mainframe can be remotely powered on by simply ap-
plying an 18 - 28 VDC control voltage to the terminals of its re-
mote interface connector. Connecting a simple detector circuit to
the remote interface of a mainframe also allows remote warning of
a mainframe fault. Details of basic circuits for remote power cont-
rol and fault display are published in d&b technical information
bulletin TI 212.
