The principle:
Up to 16 PEM expansion modules can be connected to the RTU radio modules via an extension port to expand the number of inputs and outputs. Analog output modules are also available. Upon powering on the radio module, the port is scanned, and the RTU automatically detects the number of its I/O points.

Local Bus connection: 
The first expansion module is connected via the expansion port of the base radio module. The base module is linked to the first I/O module, and from the right socket, the connection can continue to the next I/O module. A 6-pin RJ connection cable is used for this purpose, typically 10 cm in length, with a maximum allowable length of 50 cm per cable.

Overview of Expansion Modules:

• PEM-04AO
  Expansion Module with 4 Analog Outputs:
  The 04AO module features 4 analog outputs with 0–10 V and 0–20 mA. The voltage and current signals control both outputs simultaneously.
• PEM-08AI
  Expansion Module with 8 Analog Inputs:
  The analog inputs are designed as current inputs and can be driven by 0–20 mA and 4–20 mA sensors. The input resolution is 12 bits.
• PEM-16DIO
  Expansion Module with 16 Digital Inputs and 16 Digital Outputs:
  Binary Inputs: The 16 galvanically isolated binary inputs (via optocouplers) can be used in groups of 4, configured as either positive or negative switching.
  Binary Outputs: The galvanically isolated PNP switching transistors (positive switching) can handle up to 500 mA and are designed for operation at 12 V to 24 V.
• PEM-16DI (32DI)
  Expansion Module with 16 (32) Digital Inputs:
  The module features digital inputs for voltages from 10 to 30 V DC. The galvanically isolated binary inputs (via optocouplers) can be used in groups of 4, configured as either positive or negative switching.
• PEM-16DO (32DO)
  Expansion Module with 16 (32) Digital Outputs:
  The modules feature 16 (32) digital outputs for switching voltages between 10 and 30 V DC.
• Power Supply Module PNT24
  Power supply module for integration into the extension module bus to provide power to expansion modules without their own power supply connection, supporting voltages of 12–24 V DC. Additionally, the module serves as an amplifier/repeater for all signal lines.
• Time Server PTS-100
  The PTS-100 generates a DCF-77 time signal from various reference sources and extends the standby time of central radio devices (TRM, RTU, and MDP) in case of reference source failure.
  
  Reference Sources for the Time Signal:
  
  • GPS (Global Positioning System), GPS antenna included in the scope of delivery
  
  • DCF-77, (Active DCF-77 receiving antenna available as an optional accessory) 
  
  • RTC (Real Time Clock) Integrated real-time clock for fallback in case all other sources fail