Understanding Dry Contacts: Guide for Industrial Monitoring Systems

Understanding Dry Contacts: A Comprehensive Guide for Industrial Monitoring Systems

In industrial monitoring, dry contacts play a crucial role in system integration. They enable secure communication between devices without supplying power themselves, protecting sensitive systems from electrical interference. This article explains what dry contacts are, the types available, how isolation technology works, and how to choose the right modules for AKCP SensorProbe+ devices.

What Are Dry Contacts?

Dry contacts, also known as volt-free or potential-free contacts, are switches or relays that do not supply their own voltage or current. They open or close a circuit to indicate status changes without injecting energy into the monitored system. This isolation is especially useful when connecting external devices like alarms, UPS systems, or HVAC controllers, avoiding electrical hazards or interference.

Unlike “wet contacts,” which have voltage applied directly, dry contacts remain neutral until connected to an external circuit. Common uses include door monitoring, smoke detectors, or equipment failures. For example, a dry contact may close when a smoke detector triggers, sending an alert to monitoring software without voltage conflicts or ground loops.

Dry contacts are highly versatile, enabling integration of third-party systems into monitoring platforms such as AKCP SensorProbe+ network-enabled devices.

Types of Dry Contact Modules on AKCP Devices

AKCP offers several dry contact modules for their SensorProbeX+ base units. These modules expand functionality and support up to 30 dry contact ports on a single 1U rack device. Additional modules can be added via expansion units, allowing flexible configuration depending on the number and type of contacts to monitor.

• Isolated Contacts (D1i/D2i): For safe, general-purpose measurements on volt-free systems. Isolation protects against electrical interference and ensures safety. Ideal for standard monitoring where isolation is important, such as connecting sensitive equipment.
• I/O Contacts (D1/D2): Allow both output of dry contacts to control external devices and monitoring of volt-free inputs. Without additional isolation, suitable for simple applications such as activating relays or reading binary states.
• 20VDC Contacts (D1iV/D2iV): For DC signals between 5–20 V. Isolated versions provide protection while handling low-voltage signals, e.g., from power relays or control panels.
• 20VAC Contacts (D1ACV/D2ACV): For AC signals of 5–20 VAC. Monitor external AC inputs such as HVAC systems or older industrial controls. Isolation protects against electrical hazards.

Modules are available in 10 or 20 port versions (D1 = 10 ports, D2 = 20 ports), making AKCP SensorProbeX+ devices scalable for data centers or industrial applications.

How Isolation Technology Works in Dry Contacts

Isolation electrically separates the input (monitored side) from the output (monitoring device), preventing direct current flow. This protects against ground loops, voltage spikes, or interference that could damage equipment or trigger false alarms.

The most common method is optical isolation (opto-coupler), consisting of an LED and phototransistor in a light-proof housing:

• Signal Detection: When the dry contact closes/opens, a small current activates the LED on the input side.
• Optical Transmission: Light activates the phototransistor on the output side, switching the circuit without direct electrical connection.
• Isolation Barrier: High-voltage transients on one side do not affect the other.

Other isolation methods include magnetic (transformers) or capacitive coupling, but opto-isolation is reliable and cost-effective. In AKCP modules like D1i or D1iV, this technology protects inputs and is ideal for harsh industrial environments. It also extends the lifespan of connected systems by minimizing electrical stress.

How to Choose the Right Dry Contact Module for Your AKCP Device

The choice depends on your application and interface type. Steps:

1. Check the interface type: Volt-free or voltage signal? For volt-free systems, use D1i/D2i (isolated) or D1/D2 (basic I/O).
2. Check voltage range:
   • DC signals 5–20 V → D1iV/D2iV
   • AC signals 5–20 V → D1ACV/D2ACV
3. Prioritize isolation: In environments with potential electrical interference, high voltages nearby, or sensitive equipment, always select isolated modules.
4. Test and configure: Use AKCP software to configure alerts, check NO/NC states, and define thresholds.

Choosing the correct module prevents false alarms and protects equipment from damage.