Didactum Knowledge Base · Didactum Devices
Dry Contact Expansion Unit
Overview of the device, connections, and technical data of the Didactum Dry Contact Expansion Unit – the CAN bus expansion module with 32, optionally 64, dry contacts for all Didactum monitoring systems with a CAN bus port.
What makes the Dry Contact Expansion Unit stand out
A simple, cascadable CAN bus expansion for IP-based monitoring of large numbers of dry contacts.
32 dry contacts
32 digital inputs for alarm and switching contacts as standard, expandable to 64 with an add-on board.
2× CAN port, cascadable
Two equivalent RJ12 CAN connections – up to 8 units can be chained per CAN bus branch.
Automatic detection
All connected contacts are detected automatically (Autosense) and displayed in the web interface.
Long range
Up to 225 m of cable length per CAN bus branch – ideal for large infrastructures and expansive buildings.
Flexible mounting
Can be mounted in a 19″ rack, on a desktop, or on a wall.
Compatible with all CAN-enabled systems
Can be used with any Didactum monitoring system with a CAN bus port, e.g. 50T, 100T, 300T, 500T, and 550T.
Low power consumption
Only 1 watt of power draw, powered via the CAN bus – optionally supplemented by the CAN-12V-1A power supply for larger chains.
Made in EU
Rugged housing, simple installation, German support included.
Typical application examples
- TCP/IP connectivity for existing systems and equipment with alarm or switching contacts
- IP integration of heating, ventilation, and air conditioning (HVAC) systems
- Integrating emergency power and fire detection technology into network monitoring
- Integrating building technology into SNMP-compatible management software
- UPS monitoring by coupling emergency power and battery systems
- Access and door monitoring for server cabinets and technical rooms
- Monitoring pumps, fans, and other building technology
- Scaling large infrastructures with extensive fault reporting technology
Connections & controls
All connections, LEDs, and switches on the front and back of the Dry Contact Expansion Unit at a glance.
The rear features the terminal blocks for the dry contacts, while the front houses the status LEDs for fault and operation indication, the two CAN ports, and the termination switch.
Rear – connections 1–2
Rear: terminal blocks for dry contacts 1–32 and the optional slot for 33–64.
Dry contacts 1…32
Terminal blocks for the 32 dry contacts included as standard.
Dry contacts 33…64 (empty slot)
Reserved slot for the optional "VT32 / Dry Contacts Board" that expands the unit to 64 dry contacts. The board is ordered separately.
Front – connections 3–6
Front: status LED for fault/operation, RUN/ERR status LEDs, CAN ports 1 and 2, and the TR termination switch.
Status LED (device fault / operation)
Indicates whether the device has a fault or is operating normally.
Status LEDs (RUN, ERR)
"RUN" shows the connection status to the main module, while "ERR" indicates that the connection to the main module has been lost.
CAN 1 / CAN 2
Two equivalent, digital RJ12 connections for linking to the main module, CAN sensors, or additional CAN expansions, with automatic detection.
TR termination switch
The switch closest to the CAN input. Set to "ON" for the last unit in the CAN chain. For long chains over 10 m, the terminator on the last unit should be set to "OFF." Note: The "FR" DIP switch (labeled "1") must always remain "OFF" — switching it to "ON" shuts the module down. It is used exclusively for programming purposes.
What's included in the delivery
Please check the delivery for completeness upon receipt and report any missing or damaged parts to your supplier immediately.
- Dry Contact Expansion Unit1 piece
- RJ12 patch cable, 2 m1 piece
- Quick guide1 piece
Available as an option: the "VT32 / Dry Contacts Board" for expanding to 64 contacts (factory installation available on request), as well as the "CAN-12V-1A" power supply for additional power on longer CAN bus chains.
Dimensions in detail
Technical data
Function
| Device type | CAN bus expansion module for dry contacts |
|---|---|
| Function | Adds additional dry contacts to Didactum monitoring systems |
| Integration | Flexible via the CAN bus, compatible with additional CAN sensors and expansions |
Inputs/outputs & communication
| Dry contact inputs (standard) | 32 (2-wire connection) |
|---|---|
| Dry contact inputs (max., with VT32 board) | 64 |
| CAN connections | 2× RJ11/RJ12 6P4C |
| Network interface | CANopen |
| Daisy-chain support | Yes, up to 8 units per CAN bus branch |
Expansion
| Expansion module | Dry Contacts Board (optional, sold separately) |
|---|---|
| Effect | Adds 32 additional contact inputs to the unit |
| Maximum configuration | 64 dry contacts per unit |
Power supply
| Power consumption | 1 watt |
|---|---|
| Supply | Via the CAN bus from the main module; for larger installations, the CAN-12V-1A power supply is recommended |
| Max. distance to main module | 225 m per CAN bus branch |
Environmental conditions
| Optimal operating temperature | -10 to +80 °C |
|---|---|
| Extended temperature range | -40 to +100 °C |
| Storage temperature | -40 to +100 °C |
| Operating and storage humidity | 0 to 95% |
Mechanics & mounting
| Dimensions (W × H × D) | 215 × 40 × 40 mm |
|---|---|
| Weight | approx. 0.77 kg |
| Status indicators | Red (fault), green (operation) |
| Mounting options | 19″ rack, desktop, wall mount |
General
| Country of manufacture | EU |
|---|---|
| Compatible systems | All Didactum monitoring systems with a CAN bus port (including 50T, 100T, 300T, 500T, 550T) |
Frequently asked questions
What is the Dry Contact Expansion Unit and what is it used for?
The Dry Contact Expansion Unit increases the number of dry contacts that can be connected to a Didactum monitoring system. Each unit provides 32 additional digital contact inputs and is suitable for IP-based remote monitoring of alarm and switching contacts in server rooms, building technology, and industrial facilities.
How many contacts does the unit support, and how can it be expanded?
As standard, the unit offers 32 inputs for dry/digital contacts. With the optional "Dry Contacts Board," this can be increased to up to 64 contacts per unit. Installation of the add-on board can be carried out at the factory upon request.
How is the unit connected to the monitoring system?
Thanks to CAN bus support in Didactum IP alarm systems, the unit is simply connected to one of the main module's two CAN bus ports. A 2 m RJ12 patch cable is included in the delivery. Up to 8 units can be chained per CAN bus branch, with each branch reaching a total length of up to 225 m.
What does the TR termination switch do?
The TR switch terminates the CAN dry contact unit and helps prevent interference signals on the CAN bus. The last unit in a serial CAN bus chain should always be terminated (TR "ON"); for chains longer than 10 m, the terminator on the last unit should be set to "OFF." The separate "FR" DIP switch is used only for programming purposes and must remain permanently "OFF," as the module will otherwise shut down.
How are the individual contacts configured in the system?
Once the unit is connected, all contacts are detected automatically (Autosense) and displayed in the web interface of the Didactum monitoring system. There, each contact can be individually named (e.g., "UPS System 1" or "Server Room Door"), its normal state (NO/NC) defined, and custom alarms or actions configured — such as an SNMP trap or SMS notification if an air conditioning unit fails.
Which Didactum monitoring systems is the unit compatible with?
The Dry Contact Expansion Unit can be connected to any Didactum monitoring system with a CAN bus port, including the 50T, 100T, 300T, 500T, and 550T models, as well as compatible PDU systems. All events are logged centrally in the syslog of the respective main system.
Questions about the Dry Contact Expansion Unit?
Our support team in Germany is happy to advise you free of charge on selection, setup, and CAN bus wiring.