Section 4
TM6564-C-00
26 April, 2011
4-2
4.4.
PROTECTION FOR DEVICES CONNECTED TO THE SCANNER
Some devices such as standard cells can be damaged if two relays on the same output line
are closed at the same time. The Guildline Instrument Limited scanners have three
methods to protected devices connected to the scanner inputs.
Two of the three protection schemes can be seen in Figure 4.1. The first one is in the logic
itself. The data at the selector is in six bit binary. Thus only one of the 64 relays can be
activated for any possible combination of the six input lines. If a failure should occur in
the bus interface, encoder or selector circuits, or if an incorrect message is sent over the
bus, no devices will be damaged because only one relay can be closed.
32 to 5
Line
Encoder
A / B
Selector
BUS
Inter-
Face
BUS /
Push-
Button
Selector
6 TO 64
Line
Decoder
and
Relay
Drivers
Logic
Control
Circuit
A Line
B Line
GPIB
Inputs
Rem ote
+5 or
+15V
A Close
Gate
To Relay
Clear Ckt
A
B
To Rear
Panel
32 B Relay Contacts
Series Protect Lines
B Clos e
Gate
32 A Relay Contacts
16 or 32 Front Panel
Relay Selector
Pus hbuttons
(16 or 32) A-Line
Relay Coils
(16 or 32) B-Line
Relay Coils
Figure 4-1: Functional Diagram of Scanner
Channel
Selector
