Dry Contact Transmission over IP Network with NetRelay

Within the scope of this project, a NetRelay-based communication system was developed to transmit dry contact signals between geographically separated devices over an existing IP network without installing dedicated long-distance control cables.

The system enables dry contact signals received from alarm panels, generators, UPS systems, fire alarm systems, pumps, sensors, door contacts and industrial machines to be transferred to a remote relay output over Ethernet, Wi-Fi, the internet or a VPN connection.

How Is a Dry Contact Signal Transmitted?

The dry contact output of the source equipment is connected to a NetRelay digital input. When a change in the open or closed state is detected, the information is transmitted over the network to a NetRelay device at the destination. The corresponding relay on the destination device opens, closes or generates a timed pulse according to the configured scenario.

This allows the physical contact state at one location to be reproduced as an actual relay output at another location, even when the two sites are many kilometers apart.

Point-to-Point Contact Transmission

Two NetRelay devices can be paired to establish a direct connection between a digital input and a relay output. When the input on the source device becomes active, the relay on the destination device is automatically activated. When the input returns to its inactive state, the relay returns to its predefined normal condition.

Multi-Site Central Communication

Using an MQTT infrastructure, multiple branches, facilities and field devices can communicate through a central system. A signal received by one NetRelay input can be transmitted to one or multiple remote NetRelay devices. Alarm and status information received from different locations can also be collected and monitored at a central control point.

Monitoring and Control

The real-time status of digital inputs and relay outputs can be monitored through centralized management software. Authorized users can remotely control relays, configure automated scenarios and record every contact state change with its timestamp.

Connectivity and Safety Scenarios

Project-specific fail-safe scenarios can be configured so that relay outputs maintain their current state, return to their normal state or switch to a predefined safe condition during a communication failure. Periodic connection monitoring can identify whether the remote NetRelay device is online and generate an alarm when communication is interrupted.

For internet-based applications, security measures such as VPN connectivity, user authentication and authorized MQTT connections can be implemented.

Application Areas

• Transmission of alarm and fault signals to a remote monitoring center
• Transfer of fire panel contact signals between buildings
• Monitoring the status of generators, UPS units and energy systems
• Remote triggering of doors, barriers and turnstiles
• Control of pumps, fans, sirens and lighting systems
• Transmission of flood, temperature and motion sensor alarms
• Transfer of machine status information between factories
• Control of base stations and remote field equipment
• Sharing alarm and contact information between branches
• IP-based communication as an alternative to long-distance control wiring

Project Advantages

• Uses existing Ethernet and Wi-Fi infrastructure
• Reduces the cost of long-distance control cabling
• Fast and real-time dry contact transmission
• Software integration through MQTT and REST API
• Ability to transmit one input signal to multiple destinations
• Logging of contact state changes
• Connection failure and device status monitoring
• Scalable and modular architecture