Rugged Ethernet IO Device with 4 Digital Inputs for Monitoring and Alarming​

Ethernet IO - Smart 4 Input Sensor
Smart 4 Input Sensor

Ethernet I/O

RLH Smart SeriesThe Smart Input Sensor is a Ethernet device with 4 digital inputs. The device allows for web based monitoring of the inputs and may be integrated into distributed control and network management systems to allow those systems to alarm and monitor field devices. Each of the Inputs can be individually configured to send customized emails and notifications when an event is recorded. The device supports a wide variety of protocols it is compatible with over Ethernet. Integration options supported are: SNMP Polling and Traps, Modbus TCP featuring addressable registers, and DNPv3 TCP for integration with utility and other automation control systems.

Contact Closure Over Ethernet

The RLH Smart Input Sensor has the ability to be paired with an RLH Relay Output Device. When using RLH’s System Link feature, the two devices become linked establishing a tunnel over an Ethernet network and will transport a digital output signal being received by the Input Sensor through the Ethernet tunnel to the linked Relay Output device. The System Link feature can be set up via: One to One, Many to One, and One to Many allowing for event distribution and consolidation as needed.

View the matching Smart 4 Relay Output


  • Rugged Design – Operating temperature, -40°C ~ 70°C
  • Intuitive embedded web interface for configuration
  • 4 inputs for multiple alarm monitoring
  • Supports SNMP 1, 2c, 3, & SNMP Traps 1, 2c
  • Supports DNP 3.0 over Ethernet
  • Supports Modbus over Ethernet
  • Use the System Link feature to Pair this device with a Relay Output for alarm transportation over Ethernet
  • Supports a One-to-Many Feature, Send alarms from one location to multiple Relay Output devices
  • Email alarms for the Inputs are customizable to your application
  • Advanced SMTP integration allowing for SSL and TLS based authentication
  • Event log with time stamps
  • Each digital input is optically isolated
  • System power ranges available: 24-48VDC or 125VDC
  • PoE Powered device – Can be powered by any IEEE 802.3af compliant PoE source
  • 10/100 Fast Ethernet Port
  • Limited Lifetime Warranty
  • Made in USA

Powering Voltage:
Standard Model – 24-48VDC
-A Model – 125VDC
-B Model – 12VDC

PoE Powered Device:
IEEE 802.3af compliant (Compatible with mode A & B PoE sources)

Power Consumption:
6 Watts (Maximum)

Protocols Supported:
DNP 3.0 TCP, Modbus TCP, SNMP Polling 1,2c,3, SNMP Traps 1, 2c, SMTP w/ TLS Authentication

System Link Response Time:
Typical 8ms, Maximum 45ms
One-To-Many (UDP) < 15ms Many-To-One (TCP) < 250ms

*Specifications listed are based on direct connections. Network overhead should be considered when calculating overall system response times.

Data Interface:
Ethernet (RJ-45)

Data Rate:
Fast Ethernet 10/100Mbps

Inputs 1~4:
Polarity Insensitive
Optical isolation 3.5kV
SM-IN4-DR-2 Dry: Sourcing Input (100 ohms maximum loop resistance)
SM-IN4-12-2 Wet: Sinking Input (5~15VDC / 5mA)
SM-IN4-48-2 Wet: Sinking Input (20~52VDC / 5mA)

LNK – System Link ON/OFF Status
Outputs – ON/OFF Status

System Alarm Output:
NO/NC Relay

Surge Protection:
Varistors & Automatic resettable fuses
DC Input Isolation 1.5kV
Voltage Reversal Protection

Powder coated steel and aluminum alloy
Physical Dimensions H 4.93” x W 1.20” x D 3.93” (125mm x 31mm x 100mm)

Mounting Style:
Standard DIN rail (T-35)
Wall Mount

Temperature -40°F to +158°F (-40°C to +70°C)
Humidity 95%
MTBF 175,000 Hrs. (Circuit Board level)

General Information


Contact Closure over Ethernet - One to One (TCP)
Contact Closure over Ethernet – One to One (TCP)
Contact Closure over Ethernet - One to Many (UDP)
Contact Closure over Ethernet – One to Many (UDP)
Event Consolidation - Many Inputs to One Output
Event Consolidation – Many Inputs to One Output
Wet or Dry Contacts – Integrated Solution
Wet or Dry Contacts – Integrated Solution


Lead Time: 1 Week*

For product questions, volume pricing and/or delivery outside of the US and Canada, please contact sales.


Smart 4 Input Sensor

Product configurationInputsInput TypePart numberPrice
4 Digital Inputs, 24-48VDC Digital Inputs4 Digital Inputs24-48VDCSM-IN4-48-2$395.00
4 Digital Inputs, 3-15VDC Digital Inputs4 Digital Inputs5-15VDCSM-IN4-12-2$395.00
4 Digital Inputs, Dry Contact Sensing Inputs4 Digital InputsDry Contact SensingSM-IN4-DR-2$395.00
  • For the 125VDC input power option, please note your part number, add -A to the end, and get your quote here
  • For the 12VDC input power option, please note your part number, add -B to the end, and get your quote here.

Smart 4 Relay Output

Product configurationOutputsOutput TypePart numberPrice
4 Relay Outputs, Normally Open4 Relay OutputsNormally OpenSM-OUT4-NO-2$395.00
4 Relay Outputs, Normally Closed4 Relay OutputsNormally ClosedSM-OUT4-NC-2$395.00
  • For the 125VDC input power option, please note your part number, add -A to the end, and get your quote here
  • For the 12VDC input power option, please note your part number, add -B to the end, and get your quote here.

*Lead times are estimates and may vary. You will be contacted within 1 business day to go over the details of your order. If you require a specific date, let us know!
*Days = Business Days

WarningWarning: This product can expose you to chemicals including arsenic, which is known to the State of California to cause cancer. For more information, go to

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