MRV Communications LX-4000 Series - Manual (Page 43)

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Alternative Port Capabilities
Alarm Inputs use the LX-Series input circuits (DSR and CTS) to detect level transitions. These input
circuits sit at the 0V level when left unconnected and can accept a voltage input in the range of ±10V.
Figure 20 - Typical Alarm Inputs Connections
An external voltage within the range of ±10V is required in order for a change to be detected when the
contact opens or closes. Typically, an LX-Series Control Output is used to provide the controlling
voltage for the Alarm Inputs, but it is not required. An external voltage could be used as long as it is
within both the ±10V limits and the limits of the contacts or semiconductor used in the circuit. A
common Signal Ground is required. Refer to Figure 20 for typical implementations.
Important design issues to remember are:
• Electro-mechanical contacts must be rated up to 10V and 3.5mA.
• The inputs present a nominal 5K Ohm impedance but can vary from 3K to 7K Ohm.
• Input levels must be 0.6V or lower to guarantee a low state and 2.4V or higher to guarantee a
high state.
• LX-Series products do not support the use of TXD as the controlling voltage for Alarm Inputs.
DTR or RTS must be used.
• DTR or RTS can provide the controlling voltage for up to 2 Alarm Inputs each.
• A common Signal Ground is required. Twisted pair connections are recommended to reduce
sensitivity to noise.
Note that provisions for handling alarm contact bounce and alarm flooding are available in the IR-
7104 Alarm Manager family only.
Control Output Setup and Usage
The LX-Series can be configured to provide two low voltage/low current Control Outputs per port
using the DTR and RTS output signals. Typically the Control Output is used as the controlling
voltage for the LX-Series Alarm Inputs. In another case you can design an interface to transition
from the output signals to a higher capacity circuit to implement a control subsystem. An example
circuit is shown in Figure 21.
Important design issues to remember are:
• Special design attention is required when using Control Outputs in a control subsystem.
• Upon a restart or power up the states of DTR and RTS will transition several times as the LX-
Series begins its start-up initialization.