NTX-U20 ( GE D20 Upgrade )

Design Features

The Advanced Control Systems (ACS) NTX-U20 is a cost-effective and feature-rich upgrade solution for General Electric D20 I/O peripheral panels. The NTX-U20 mounts directly to the existing WESTERM 

termination boards, eliminating the need to disturb or replace any of the existing field wiring. For the utility, this means up to 60% cost savings over a traditional RTU replacement, since the work required to re-produce drawings, perform re-cabling and do extensive point checkout is vastly reduced. Existing installations can also be expanded through the addition of ACS I/O modules to the NTX host, or the use of ACS-designed replacements for the old WESTERM termination panels.    


Design Features:


  • Powerful, open-system architecture based on ARM 9E 32–bit RISC processor and Linux OS
  • Can be integrated with the ACS NTX-200 series substation controllers as the master, or with another substation control platform
  • Plugs directly into existing WESTERM termination panel - no need to touch the existing wiring
  • No changes to the existing SCADA system database are required when using the same master protocol
  • Replaces proprietary protocol between modules with DNP 3.0 – opening up the system for easy expansion 
  • Dual Ethernet ports support DNP3 or Modbus TCP/IP or UDP client, server or multiples of both; also functions as integrated 2-port integrated Ethernet switch
  • Large 14,000 point database capacity per module
  • Provides time synchronization via IRIG-B (un-modulated), GPS satellite clock, NTP or DNP3 protocol 
  • Easily expandable through the addition of ACS I/O modules to an NTX-series host controller, or through the use of ACS-produced replacement termination panels paired with additional NTX-U20 units
  • Available IEC 611131- and 61499-compliant logic virtual machine executes user-defined algorithms on any NTX-U20 module
  • Easily configured using our intuitive, Windows-based NTX Explorer application


Application and expansion:


The NTX-260 is typically used in a traditional centralized 19” equipment rack or cabinet. An NTX system controller with termination provides a combination of router and dual-serial ports, with a 10/100 BaseT Ethernet port gateway as the base communications. The router component acts as an NTX internal network controller, where the map of all physical to virtual data is stored. A binary output controller supports up to 256 external control relays with both momentary (varying contact voltage/current ratings support) and latch relays. The local input controller supports up to 256 16-point Analog Input modules, 512 32-point Digital Input modules and 16 external DC Analog Output channels. 




I/O requirements beyond the base 8-slot I/O motherboard for analog and/or digital input modules are configured in an external expansion I/O card File, with 8 or 16 additional I/O motherboard slots. The unit power supply and up to seven additional NTX Quad-Serial with Ethernet port gateways can be incorporated in the card file mid-plane system motherboard—for a total of 30 isolated EIA561 RS-232/RS-485 RJ45 serial ports and 8 high-capacity 10/100 BaseT Ethernet ports. The local I/O node controllers will use two of these slots when configured. 


NTX Explorer software makes it easy to configure or expand the type and number of ports and protocols communicating with the master stations or IEDs, defining local I/O points, and/or other components. 


Control Adapter Module


For sites that have hand-wired, heavy-duty relay panels or other control interfaces, ACS has developed an external adapter module for the NTX-U20/K and NTX-U20/C models. It has appropriately rated Form A and Form C relay contacts that emulate the original General Electric D20 isolated relay driver logic. These relay drivers can support external relay coils rated at 24 VDC, 48 VDC or 130 VDC of either polarity. We are also developing adapters for the various connector or terminal block interfaces supported in the original GE D20 K WESTERM base board, so all known external interposing relay installations can be accommodated beyond the basic KI relay modules.


Replacement Termination Panels

In addition to the NTX-U20/KT termination panel for the U20/K module, ACS also offers form-fit termination panel replacements for the following WESTERM panels:

   GE D20S (NTX-U20/DT)

   GE D20A (NTX-U20/AT)

   GE D20C (NTX-U20/CT) 



The NTX-U20/A panel is the retrofit module for the GE D20A. It replaces the WESDAC Analog Logic Panel with a form-fit NTX-U20 I/O Controller and a 32-point piggy-back Analog Input Module, providing plug-in interfaces to the original WESTERM Termination Panel. All analog inputs are differential and bi-polar. The NTX-U20/A utilizes a 16-bit A/D Converter. The calibration resistors and transient protection circuitry are maintained on the original WESTERM termination panel. The NTX-U20/A analog system is compatible with the original General Electric D20A peripheral panel inputs. Existing single or redundant 24 VDC or optional 48 VDC power supplies can be utilized or replaced as part of the upgrade.


The NTX-U20/D is the retrofit module for the GE D20S status input panel. It replaces the WESDAC Digital Logic Panel with a form-fit NTX-U20 I/O Controller, with a 64-point Digital Input Module providing plug-in interfaces to the original WESTERM termination panel. A variety of input types are configurable per point, including Status, SOE and accumulators. Each input supports time tagging of changes as detected to a resolution of 1ms. Contact wetting is provided from either the on-board General Electric D20 24 VDC or optional 48 VDC power supply, or an external supply (e.g. station battery, etc.) as originally configured.



The NTX-U20/K is the retrofit for the GE D20K, and replaces both the WESDAC Control Logic Module and the WESTERM base panel. The NTX-U20/K provides a 16x16 isolated high-current optical driver matrix that replaces the GE WESDAC D20K physical relay drivers. The matrix supports two strings of 128 relays each, with up to 256 control relays (128 trip/close pairs), using the original external WESDAC interposing relay panels. The NTX-U20/K supports assigning relay contact closure times in one–millisecond increments for each relay via DNP3.


All of the original external General Electric D20KI series interposing relay panels are maintained with the upgrade, and replacement interface cables are provided. A local/remote switch is also provided on the form-fit replacement termination panels. The single or redundant 24 VDC or optional 48 VDC power supplies may be utilized or replaced as part of the upgrade. 



The NTX-U20/C is the retrofit module for the GE D20C combination logic panel. It replaces the GE WESDAC D20C Combination I/O Logic Panel with a form-fit I/O Controller that includes a 16-point Digital Input Module, 16-point Analog Input Module (not an option with the NTX-U20/C) and an isolated high-current optical control relay driver controller for up to 32 interposing relay outputs (16 trip/close pairs).


The NTX-U20/C provides plug-in interfaces to the original General Electric D20C WESTERM termination panel for analog and digital input wiring connections, and a control relay cable for connection to external KI series momentary or latching interposing relay panels. The NTX-U20/C does not support analog outputs and pulse control (AGC). The NTX-U20/C supports assigning trip/close contact closure times in one–millisecond increments for each relay via DNP3.


More Information

For more information call 800.831.7223 or contact This email address is being protected from spambots. You need JavaScript enabled to view it.



ACS NTX-U20 ( GE D20 Upgrade ) controller Brochure PDF


ACS NTX-U20 Controller (GE D20 UPGRADE) Product Brochure