iSensor Volt Free Contact (VFC) for iSensor & iAccess Controllers
Volt Free Contact Sensor: Monitor and Alert Open/Close Devices
The Advanced Datacentre Systems iSensor Volt Free Contact (VFC) helps you monitor devices. To enhance security auditing, this optional sensor tracks the physical open/close state of contacts. Instantly flagging potential issues within the data centre.
This sensor sends simple open or closed signals to your monitoring software. You can connect it to platforms like:
- NMS (Network Management Systems)
- BMS (Building Management Systems)
- DCIM (Data Centre Infrastructure Management)
Use it to check if a door is open, a switch is on/off, or a breaker has tripped.
Learn more about Environmental Monitoring by reading our Essential Guide to Environmental Monitoring in Data Centres.
Product Overview
What Is the iSensor Volt-Free Contact (VFC)?
The iSensor Volt-Free Contact (VFC) is a simple, reliable sensor that functions as a voltage-independent, mechanical switch. Unlike a traditional switch, it does not generate electrical power. Instead, this smart device makes it easy to share information. It sends updates about whether circuits are open or closed. This information goes straight to your IT, facility, or data centre systems. It uses standard communication methods that all these systems understand.
Our “dry contact” design solves a common problem. It stops voltage differences from causing issues. This means you can easily connect it to your existing systems. It works with infrastructure management platforms like NMS, BMS, and DCIM.
How Does the VFC Work?
The VFC connects to an iSensor or iAccess controller with a standard CAT 5/6 Ethernet cable. You can use cable runs up to 500 metres, which gives you plenty of installation options. The device uses a basic mechanical switching action. When a door opens, a panel triggers, or a linked system changes state, the contact either closes or opens. The controller reads this change and sends the event to your chosen platform.
You can set the device as Normally Open (NO) or Normally Closed (NC). This helps you match the sensor to different operational needs. The VFC also includes a 100ms anti-bounce time. This short delay stops rapid flickering of the switch from creating false alerts.
The VFC gives you a safe and isolated connection point. Because the contact is “volt-free,” it never introduces voltage into a circuit. You supply the voltage that drives the signal. This protects your systems from electrical conflicts and makes the VFC suitable for a wide range of equipment. Many teams choose dry contacts because they reduce risk, keep wiring simple and help avoid interference between systems.
Built for Real-World Data Centre Needs
Data centres rely on accurate and fast signalling. The VFC sensor supports this by keeping its design simple and robust. It uses an RS485 interface at 9600 baud rate, with an 8 data-bits, 1 stop bit, no parity configuration. This keeps communication stable and predictable. The device also runs on very low power: 5 V DC at 100 mA, with an internal 3.3 V supply that draws only 50 mA. This reduces heat, keeps energy use low and helps ensure long-term reliability.
Where You Can Use VFC Sensors
Facility teams often use the VFC sensors to track door contacts, security panels, equipment alarms, airflow switches, power events and many other binary signals. Because the device offers complete electrical isolation, it suits almost any system that outputs an open/close contact. You can also integrate it into safety systems, interlocks, threshold triggers or backup equipment.
Why Dry Contacts Help
The VFC iSensor converts simple dry contact inputs into clear, actionable data.
You gain instant visibility of critical events. This setup lets you spot problems early and maintain strict control. The VFC scales with ease, supporting long cable runs and flexible mounting options. Simple wiring ensures high compatibility. Deploy it immediately into any existing system.
Features & Benefits
- Connects via standard CAT 5/6 Ethernet cable
- Supports up to 500 metres of sensor cable
- Offers Normally Open (NO) or Normally Closed (NC) contact types
- Anti-bounce time of 100ms to reduce false triggers
- Maximum contact resistance: 2 kΩ
- Uses RS485 interface with 9600 baud, 8 data bits, 1 stop bit, no parity
- Compatible with both iSensor and iAccess controllers
- Requires only 5 V DC at 100 mA (very low power)
- Internal 3.3 V supply draws just 50 mA
- Provides isolated, “dry contact” switching for safe integration
Specification
Contact Inputs
- Type: Normally Open (N.O) or Normally Closed (N.C)
- Anti-bounce time: 100 mS
- Contact Resistance: 2k ohms max.
iSensor Port
- Interface: RS485
- Protocol: 9600 baud, 8 data bits, 1 stop bit, no parity
- Compatibility: iSensor & iAccess Controllers
DC Characteristics
- 5V Supply: 5 VDC @ 100 mAmps max
- 3.3V internal supply: 3.3 VDC @ 50 mAmps max
Frequently Asked Questions (FAQs)
What is a Volt Free Contact (VFC) sensor?
A Volt Free Contact (VFC), also known as a dry contact sensor, monitors whether a circuit or device is in an open or closed state without introducing electrical voltage into the system.
The iSensor VFC converts these status changes into monitoring data that can be sent to DCIM, BMS, or network management platforms.
What can a Volt Free Contact sensor monitor in a data centre?
The VFC sensor can monitor any device or system that provides a simple contact signal, including:
- Cabinet or room door status
- Security systems and alarm panels
- Power breaker or UPS alarms
- Airflow or cooling system switches
- Equipment fault or warning signals
- Mechanical or safety interlocks
This provides visibility of physical and operational events across the facility.
Why are volt-free contacts used in data centres?
Volt-free contacts provide electrical isolation, preventing voltage conflicts between connected systems.
This makes integration safer and more reliable when connecting monitoring platforms to third-party equipment or legacy infrastructure.
How does the iSensor Volt Free Contact work?
When a connected device changes state (for example, a door opening or breaker tripping), the contact switches between open or closed.
The iSensor or iAccess Controller detects this change and immediately reports the event to monitoring software or alerting systems.
Which controllers is the VFC sensor compatible with?
The Volt Free Contact sensor integrates directly with:
Once connected, status changes can be monitored remotely via SNMP, DCIM, NMS, or BMS platforms.
How is the Volt Free Contact sensor installed?
Installation is simple:
- Connect the sensor using standard CAT5 or CAT6 cabling
- Plug into an available controller sensor port
- Configure alarm or monitoring rules
The sensor supports cable runs of up to 500 metres, allowing flexible deployment across large facilities.
What is the difference between Normally Open (NO) and Normally Closed (NC)?
The VFC sensor supports both configurations:
- Normally Open (NO): Circuit closes when an event occurs
- Normally Closed (NC): Circuit opens when an event occurs
This flexibility allows compatibility with different equipment signalling methods.
How does the sensor prevent false alerts?
The device includes a 100ms anti-bounce delay, preventing rapid signal fluctuations from generating false alarms caused by switch vibration or electrical noise.
Can alerts be generated when a contact changes state?
Yes. When integrated with an iSensor or iAccess Controller, contact status changes can trigger:
- Email alerts
- SNMP traps
- DCIM or NMS notifications
This enables immediate response to security or equipment events.
Where are Volt Free Contact sensors typically deployed?
Common deployment scenarios include:
- Data centre rack security monitoring
- Remote or unmanned facilities
- Edge computing sites
- Power and cooling system monitoring
- Infrastructure alarm integration
Does the VFC sensor introduce voltage into connected equipment?
No. The sensor is electrically isolated and does not supply voltage, ensuring safe integration with existing equipment and preventing electrical interference between systems.
What is a dry contact sensor used for?
A dry contact sensor monitors external equipment without supplying voltage itself. It simply detects whether a device is on or off by opening or breaking a circuit. Because it is passive, it is essential for automation systems. For example, it can secure doors and gates. It can also detect water or smoke. Finally, it tracks the status of machinery
Get in touch today
To learn more about Volt Free Contact sensors or to discuss a requirement, please contact us.