Hitachi SML-110, Quick Start Manual

To order, call 
1-800-652-7276 

sts.hitiachirail.com 

RSE-3A2

 p. 1 

Wayside Products

RSE-3A2 

Rev. 4-18 

SML-110 Switch Lock and PN-150SSR Solid-State Relay 

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.