Salient Features:

  • Ethernet: RJ45 (100BASE-T / 100 Mbit/s)
  • Configuration: Web, Telnet
  • Serial interface: 1x full RS-232/RS-485 serial port
  • Full RS-232 serial port: RxD, TxD, GND, CTS, RTS, DSR, DTR, RI, CD (115,200 Bd)
  • Inputs: 2 digital (dry contact) inputs
  • Outputs: 2 NO/NC digital (relay) outputs, rated 230V/16A 
  • Box-2-Box mode: Two units can be connected back-to-back over the network and tunnel the I/O and the serial port (peer-to-peer).
  • M2M protocols: http, Modbus/TCP, Telnet, TCP Server, TCP Client/Server
  • Support for programmers: HWg-SDK
  • Free HW VSP software: Virtual serial port for Windows (NT service, x64 systems). Supports up to 100 remote serial ports. HW VSP is the world's most popular virtual serial port for Windows!
  • HWg IPRC cmd utility: Command-line utility for remote control of outputs (Windows and Linux)


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IP Relay HWg-ER02b: Web relay + full serial port over IP

Ethernet relay, DIN rail, Web interface. Features 2x DI (dry contact input), full RS-232/485 serial port, and 2x DO (relay output, 230V/16A). 
Controlled over the web or Modbus/TCP. Two IP relays connected back-to-back can extend (“tunnel”) the serial port and I/O over a LAN.

IP Relay


Relay outputs can directly switch 230V/16A AC mains, dry contact inputs can be used e.g. for buttons. The device features a full RS-232/485 serial port for connecting e.g. a RFID or barcode reader. IP Relay is fully certified to control 110/230V and fits on a DIN rail.


Ethernet IO can be controlled over the Web, Modbus/TCP or Telnet NVT.

When the IP Relay is connected to a PC over the LAN, it can work as a serial converter that connects its RS-232 over Ethernet to a Virtual Serial Port (VSP). HW group offers HW VSP – a free virtual serial port application that supports up to 100 remote serial ports (support includes Windows 7 and x64 systems). Full RS-232 serial port controls all 9 signals.

Typical applications include remote power control, opening a remote gate over a LAN (relay output) and connecting a RFID card reader (RS-232).

  • 1x full RS-232 or RS-485 serial port (terminal server, virtual port)
  • 2x digital input (dry contacts)
  • 2x digital output (230V/16A relay output)

IP Relay comparison to previous generation

  NEW: IP Relay ER02b 
IP Relay ER02a
Housing Plastic DIN rail Plastic DIN rail
DI (Digital Inputs) 2 -
DO (Digital Outputs – 110/230V / 16A relay) 2 2
Ethernet 100 Mbps 10 Mbps
RS-232 9 wires 
(full serial port)
5 wires
Max fulltime serial baudrate 115,200 Bd 38,400 Bd
Web Interface
Modbus/TCP protocol


Full RS-232 serial port

  • IP Relay HWg-ER02b supports full RS-232 serial port in hardware
  • The HW VSP application (Virtual Serial Port) supports full serial ports
  • RFC2217 can be used for third-party SW implementations
  • IP Relay HWg-ER02b also supports 9-bit data transfer over the serial port
  • IP Relay HWg-ER02b can be used as an Ethernet com port (remote serial port)


  • Link two buttons/switches to a SW application.
  • Connect your RS-232 devices to your LAN – barcode / RFID scanners, serial printers, displays.
  • The remote relay output can, for example, open a door, turn on a horn, or disconnect power. It can be used also as web relay.
  • I/O can be controlled over Modbus/TCP from any SCADA system, independently of the serial line.
  • Remote power switch (power control) can switch 230/110V AC directly.


Box-2-Box mode – 1:1 (two units connected back-to-back over a LAN)

    • Extension of RS-232 or RS-485 over the network
    • DI at one device controls DO at the other device, 1:1 (peer-to-peer)


Digital I/O transport over the Ethernet (peer-to-peer)


Usage examples

  • Connecting a RFID reader over a LAN + remote reset of associated equipment
  • Connecting a barcode reader over the Ethernet + controlling DI and DO in an application
  • Remote UPS or diesel generator monitoring with RS-232 monitoring + remote start / test over the I/O
  • Vending machines
  • Security alarms
  • Access control systems
  • Barcode scanners in combination with LAN relay (remote I/O)


User software

    • UDP Config  – Configuring the IP address
    • Hercules – Configuration (IP address, Telnet configuration) + testing utility for Windows (Serial, UDP and TCP terminal)
    • HWg IPRC cmd – Command-line control of outputs
    • HW VSP – Free HW Virtual Serial Port for Windows. 
      IP Relay also supports the VSP Multi version – up to 100 virtual serial ports on a single PC.

For programmers

System topology

Web relay, rs-232 over Ethernet, remote relay, Ethernet IO

    • TCP/IP Server   [Telnet Client -> Server]
      I/O Controller, as a TCP server, listens for incoming TCP connections from a computer (a PC or a server). When the connection is established, data in the internal buffer are transmitted, and then bidirectional communication can take place, like a common "terminal server". 
      Binary inputs and outputs can be controlled with a M2M protocol that uses an extension of RFC2217 (NVT support must be enabled). 

    • TCP/IP Client/Server    [Telnet Server <- Client]
      I/O Controller has received some data into its internal buffer from the serial port (or has detected a change at the digital inputs) and attempts to send it to the server. The unit tries to establish a connection to the specified outgoing IP address and port. If unsuccessful, it waits for about one second in the TCP server mode and then tries to establish the connection again.
      Digital inputs and outputs can be controlled with a M2M protocol that uses an extension of RFC2217, as long as NVT support is enabled and the TCP connection is established. 

    • web relay configurationWEB   [Configuration] 
      Configuration and control of I/O over a WEB interface. It can be used as Web relay.
    • Modbus/TCP   [I/O control] Serial port cannot be controlled. Digital inputs and outputs are controlled using the Modbus/TCP M2M protocol.
    • VSP (Virtual serial port) The HW VSP software, when installed on a PC with Windows, creates a virtual serial port (e.g. COM7), and the serial port at the IP Relay then works as a physical port of your PC.
    • UDP/IP Data are sent as UDP packets, without delivery acknowledgments. The UDP mode uses a sophisticated “packetiser” that allows you to specify broad conditions about what should be sent from the serial line to the Ethernet, what should not, and when. Digital inputs and outputs cannot be controlled in the UDP mode.