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5-14 Genius Modular Redundancy Flexible Triple Modular Redundant (TMR) System
User’s Manual –March 1995
GFK-0787B
Input Line Fault Detection in a GMR Application
The 16-circuit Genius blocks are capable of continually monitoring field circuits for input
short circuit or open circuit faults. The blocks detect On, Off, Short Circuit, or Open Wire
conditions on circuits set up as tristate inputs.
If a block is in a “non-GMR” mode, a resistor must be installed in the circuit to provide
Open Wire fault detection. However, if the block is in GMR mode, a zener diode is used
instead to detect short circuits. The diode is installed in series between the field switch
and the tristate input blocks, but physically at the field switch device. The Zener diode
rating is 6.2V.
V+
Block Setup for Tristate Inputs
Field
Switch
Zener
Diode
When a block is in GMR mode, the status and on/off state of a tristate input have
different specifications than they do in non-GMR mode.
Range
Non-GMR GMR
Range
Status Input Status Input
<30% VDC open circuit fault 0 off 0
>50%, < VDC+
–7V
Off 0 On 1
>VDC+ –4V On 1 short circuit fault 1
Range
Non-GMR GMR
Range
Status Input Status Input
<4V On 1 short circuit fault 1
>7V, <50% VDC+ Off 0 On 1
>70% VDC+ open circuit fault 0 Off 0
When used with a GMR block, a Genius Hand-held Monitor will correctly report a short
circuit fault instead of Open Circuit.
DC Source
Block
Tristate
Input
Thresholds
DC Sink
Block
Tristate
Input
Thresholds