Vital relays have been a mainstay for switch
machine control in the field. While they have
established an enviable history of reliable
performance, vital relays require periodic
maintenance for this degree of reliability to be
achieved. Hitachi Rail STS has developed a cost-
effective yet equally reliable alternative: The SML-
110 High Voltage Solid State Switch Machine Lock
and associated PN-150SSR relay. The SML unit
can operate two high voltage switch machines at
the same time. The PN-150SSR replaces old-style
magnetic blow-relays. This new solid-state device
is housed in the familiar PN-style case for easy
installation in existing relay racks.
General Description
The SML-110 Switch Machine Lock is a vital
conditional power supply that provides power to a
switch machine. It delivers a nominal 120 Vdc output
with a limited current of 23 amps from an ac or dc
source when activated by a nominal 12 Vdc input.
This output is sufficient to simultaneously drive two
switch machines. To deliver an output voltage, the
SML-110 requires the presence of two out of three
inputs: Switch machine lock and either the normal or
the reverse position request. These inputs can be
relay contact closures or outputs from an interlocking
processor such as our MicroLok®II system. The
output voltage of the SML -110 is fed as an input to
the PN-150SSR Solid State Relay.
The PN-150SSR Relay routes the correct polarity
voltage that is required to operate the switch machine
to either the normal or the reverse position. In addition
to the voltage from the SML-110, PN-150SSR accepts
a second input, which is either the normal or the
reverse switch request. The input can originate from
relay contacts or a vital interlocking processor such as
MicroLok II.
Product Description
SML-110 Module
The SML-110 is contained in an assembled sheet
metal housing designed for mounting on standard
equipment rack relay mounting bars. Typically, the
unit is mounted with a combination rack mounting
plate/AAR terminal board that provides AAR terminals
for external wiring. A 12-pin male connector on the
rear of the unit permits plug connection of the SML
unit to the rack mounting plate. Major subassemblies
inside the SML-110 are mounted on a chassis shelf or
are attached to the underside of the aluminum heat
sink. Components are readily accessed by removing
a 1-piece, wrap-around shell on the housing. A single
LED on the front panel of the unit indicates the
presence of output power to drive the switch machine.
PN-150SSR Relay
In the typical SML-110/PN-150SSR installation, the
SML-110 Switch Machine Lock unit serves as a vital
conditional power supply that provides power to a high
voltage switch machine. The output voltage SML-110
is fed as an input to the PN-150SSR Solid State Relay
Package.
This new relay consists of two triacs (dual solid-state
relays) housed in a PN-150 relay case. These triacs
route the correct polarity voltage required to operate
the switch machine to either the normal or the reverse
position. Each of the solid-state relays provide the
equivalent of two Form A (normally open) contacts.
Functionally, the solid state relay modules consist of
two independent SCRs that are optically isolated from
the control. One of the solid state relay modules is
used to make motor connections to drive the machine
to the normal position and the other relay module is
used to make motor connections to drive the machine
to the reverse position. Two LEDs indicate which relay
is energized, normal or reverse.
