1.535 Protection-Switch-1-To-1

The Protection-Switch-1-To-1 logical device provides a completely software based solution for a 1:1 redundancy switch. It saves the active chain (variable 'location') while the M&C is switched of and restores it at program start. This may cause a switchover at program start. For this reason, the Protection-Switch-1-To-1 logical device should only be used in applications where no position readback from the chain selecting switch is available. The Protection-Switch-NoSave-1-To-1 device provides the same functionality but relies in the switch position rather than saving the value.

The logical device monitors the fault states of a couple of devices, deriving from this the information whether to switch the (usually transmit-) chain.

As illustrated by the figure above, the redundancy switch reads up to four device fault variables for each chain and controls one switch. The latter not necessarily needs to be a waveguide switch as shown here. Any device may be configured to receive a command when the protection switch toggles the chain.

To control the switching behavior, the Protection-Switch-1-To-1 knows two configurable delay constants called 'switchDelay' and 'recovDelay'. Redundancy switch over takes place if these conditions become true at one time:

1. There was no switch over for at least 'recovDelay' milliseconds.
2. The opposite (actually redundant) chain states no fault.
3. There is a fault in at least one of the devices monitored for this (actually transmitting) chain for at least 'switchDelay' milliseconds.

When specifying the delay times, you should consider that the values become effective in steps of the IDLE time defined for the 'null' interface in the device setup. If the default value of 1000 msecs applies, all delays will be rounded up the next full second.

Redundancy switching is done fully symmetrically. There is no preferential chain. Hence the switch will not return to the initial position if the fault which caused the switch over disappears.

Operation Modes

As of version 2.02 / 080604 the Protection-Switch-1-To-1 device may be configured to act either in SW-ALWAYS or in SW-ONCE (single shot) mode.

SW-ALWAYS ist the default mode also used by earlier versions of the device. Like described above, the device will switch back to the first chain if the fault on this chain disappeared and the second chain shows a fault (eventually delayed by the recovDelay setting).

The SW-ONCE mode disables any further redundancy switching if the "switched" flag is set. This means the protection switch switches to the redundant chain and then inhibits itself. You have to click the "Reset" button at the device window to re-activate the device after a switchover.

Device window pages

The following table shows which device window pages are available with this individual device type. Tool-bar functions not mentioned here are described at the general description of device windows .

• --- This page controls the operational parameters of the device.
• --- The faults page. * --- The device info page.
• --- The maintenance page. The configuration parameters described below are set at this page.

Configuration parameters

At the maintenance page of the device window there are a couple of configuration parameter which must be set to interconnect the redundancy switch with the devices it shall monitor and control.

Fault definitions

The Protection-Switch-1-To-1 device defines a couple of individual faults to report the device's actual state. The fault conditions always are shown as LEDs at the first page if the device window. Depending on the individual fault configuration, these conditions also may be logged and summarized to a device fault for the redundancy switch. The table below describes the fault flags defined for the Protection-Switch-1-To-1 device.

• Single Fault --- Becomes true if at least one of the configured fault inputs becomes true. This also means that -- if the switch over already has occurred -- the protection switch actually is not able to compensate a possible fault in the remaining chain. Enable this fault if you want to be warned in this case.
• Double Fault --- In each chain at least one device reports a fault. The (transmit-) facility probably is not operable in this case.
• Path Select Switch --- This flag simply maps to the fault selected with the 'switchFaultId' configuration variable.
• Protection --- The protection switch raises (and latches) this fault flag if a switch over occurs. This fault maps to the 'switched' LED at the user interface. The flag is reset if you apply a 'RESET' command to the device (this command does nothing else for the Protection-Switch-1-To-1 device. Enable this fault if you want the switch over to be signaled as a latched fault.

Variables defined by this device driver