MICRONOR
automation components
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7.
Theory of Operation
A functional block diagram is shown in Figure 11, showing the Switch Sensor, Optical Link
and Controller Module. The switch is connected by a duplex fiber optic cable of readily
available 50/125µm or 62.5/125µm multi-mode fiber. The transmit fiber guides steady
optical power from a near-IR light source to the optical switch. A second receive fiber returns
the light relaying if the switch is closed or open.
Controller
The light source power is held constant under normal operating conditions allowing for a
known system loss budget when designing a system. The optics within the switch itself are
designed to couple maximum light back into the receive fiber allowing for long distance and
chaining multiple switches.
The optical power is then detected by the Schmitt Trigger Photodetector and translated into a
logic signal depending on the power level. The photodetector operates with an active low
signal scheme allowing for a known failure state. If a fiber were to break, poor connection,
high loss, or depressed switch the controller would interpret those events as a failure or
‘EMERGENCY ON.’
The photo detector outputs a logic signal to the remaining logic circuitry which then interprets
high or low levels for the +24V and +5V digital outputs.
Switch
Digital Out
Logic
Circuitry
Relay
Contacts
Light
Source
Photodetector
850nm
1300nm
635nm
Figure 11 Block Diagram of Basic Theory of Operation for MR380 Fiber Optic E-STOP
