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MHS
MHS

ALM Maintenance Hole Sensor

The Adtran ALM Maintenance Hole Sensor (MHS) is a completely passive, fiber-based monitoring solution designed to protect critical underground fiber infrastructure from unauthorized access, vandalism, sabotage, and other physical security threats. Integrated with the ALM fiber monitoring platform, it provides continuous real-time monitoring of maintenance hole lids without requiring local power or internal electronics.

Whenever a monitored maintenance hole lid is opened or closed, the ALM detects the change in sensor status, identifies the affected location, and generates an alarm. This gives operations teams early visibility of access events and enables a faster response to potential security breaches, helping reduce network risks and costly service disruptions.

Designed for demanding underground environments, the MHS features an IP68-compliant water- and dust-proof design and has no externally exposed moving parts. Its passive architecture eliminates battery replacement, local power requirements, and wireless communication dependencies, reducing maintenance requirements while also eliminating the opportunity to jam wireless monitoring operations.

Multiple sensors can be daisy-chained on a single fiber link over distances of up to 100 km, enabling scalable monitoring of geographically distributed underground assets. Combined with 24×7 centralized monitoring and email/SMS notification support through Adtran Ensemble Fiber Director, the solution provides reliable infrastructure protection for railway, utility and telecom fiber networks.

Applications:

  1. Maintenance Hole / Manhole Monitoring: Continuously monitors maintenance hole lids and detects changes between open and closed states.
  2. Underground Fiber Infrastructure: Protects critical underground fiber access points against unauthorized access and physical security threats.
  3. Railway Networks: Monitors underground access points associated with critical railway fiber communication infrastructure.
  4. Telecom Networks: Provides centralized monitoring of maintenance holes and underground fiber access points across distributed telecom networks.
  5. Utility Networks: Protects underground fiber infrastructure used by utilities without requiring power at each monitored location.
  6. Unauthorized Access Detection: Alerts operations teams when monitored maintenance hole lids are opened or closed.
  7. Vandalism & Sabotage Detection: Provides early awareness of access events that could indicate vandalism, sabotage, or interference with fiber infrastructure.
  8. Remote & Unstaffed Locations: Enables 24×7 centralized monitoring without batteries, local electronics, or wireless communication at the site.
  9. Large Distributed Networks: Multiple MHS units can be cascaded along a single fiber link for scalable monitoring across distances up to 100 km.

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ALM Maintenance Hole Sensor
Features Specifications FAQ Downloads



Features
  • Completely Passive Operation: Requires no local power supply or internal electronics, reducing operational and maintenance requirements at underground locations.
  • Real-Time Lid Monitoring: Detects changes in maintenance hole lid status and enables ALM to generate alarms when a monitored lid is opened or closed.
  • Precise Event Identification: ALM identifies which sensor has experienced the status change, allowing operations teams to quickly identify the affected maintenance hole.
  • IP68-Compliant Robust Design: The sensor is water- and dust-proof (IP68 compliant) and has no moving parts on the outside, making it suitable for underground environments.
  • Up to 100 km Network Coverage: Cascaded sensors can be deployed on fiber links of up to 100 km, enabling monitoring across large geographically distributed networks.
  • Multiple Sensors on a Single Fiber: Multiple MHS units can be daisy-chained on a fiber-optic cable providing scalable infrastructure protection.
  • No Wireless Dependency: No wireless communication or protocol setup is required at the monitored site.
  • Improved Security Against Jamming: The passive fiber-based design eliminates the opportunity to jam wireless monitoring communications.
  • 24×7 Centralized Visibility: Provides continuous location monitoring through Adtran Ensemble Fiber Director.
  • Email & SMS Notifications: Supports email and SMS event notifications, helping operations teams respond quickly to access events.
  • Wide Operating Temperature: Supports operation from -20°C to +75°C.
  • Long Mechanical Life: Specified for 20,000 cycles, supporting long-term deployment.
Specifications

Mechanical Specifications

 

Parameter

Description

Specification

Unit

Dimensions (W × H × D)

MHS including wall mount

310 × 118 × 58

mm

Step protector

200 × 200 × 90

mm

Cycle Count

—

20,000

cycles

 

Optical Specifications

 

Parameter

Description

Specification

Unit

Reflect Band Wavelength

—

1638–1700

nm

Reflection

Closed state

> -5

dB

Opened state

< -10

dB

 

Long-Range Mode Performance

 

Parameter

Specification

Unit

Maximum Fiber Length

100

km

Maximum Fiber Loss (including all sensors on link)

32

dB

Minimum Spacing Between Sensors

200

m

 

Short-Range Mode Performance

 

Parameter

Specification

Unit

Maximum Fiber Length

20

km

Maximum Fiber Loss (including all sensors on link)

28

dB

Minimum Spacing Between Sensors

5

m

 

Environmental Specifications

 

Parameter

Specification

Temperature Range

-20°C to +75°C

IP Protection

IP68 Compliant

RoHS Compliance

Directive 2011/65/EU and Delegated Directive 2015/863 – Compliant
FAQ

What is the ALM Maintenance Hole Sensor?

The ALM Maintenance Hole Sensor (MHS) is a completely passive, fiber-based sensor designed for continuous monitoring of maintenance hole lids and underground fiber access points. Integrated with the ALM fiber monitoring platform, it helps detect unauthorized access and other physical security events.

How does the Maintenance Hole Sensor work?

Each MHS generates a reflection peak on the monitored optical fiber. When a maintenance hole lid is opened or closed, the sensor status changes. The ALM detects this change and generates an alarm identifying which sensor has been triggered.

Does the MHS require electrical power or batteries?

No. The MHS is a completely passive device and requires no local power supply or internal electronics, helping minimize maintenance and operating costs.

Can the MHS detect unauthorized access to maintenance holes?

Yes. The solution is designed to help detect access events associated with unauthorized access, vandalism, sabotage, and other security threats to underground fiber infrastructure.

Can the system identify which maintenance hole has been opened?

Yes. When a lid is opened or closed, ALM identifies which sensor experienced the change in status, allowing operations teams to determine the affected location and respond quickly.

What is the maximum monitoring distance?

The MHS supports a maximum fiber length of 100 km in long-range mode and 20 km in short-range mode.

Is the MHS suitable for underground environments?

Yes. The sensor has an IP68-compliant water- and dust-proof design and no externally exposed moving parts, making it suitable for demanding underground installations.

Where can the ALM Maintenance Hole Sensor be used?

The MHS is designed for protecting underground fiber infrastructure across railway, utility, and telecom networks, particularly where maintenance holes and underground access enclosures need continuous security monitoring.

Can multiple MHS units be monitored from a central location?

Yes. Multiple sensors can be cascaded along the fiber network while the ALM device at the central office continuously monitors the optical link. This enables centralized monitoring of geographically distributed maintenance holes.

Does the MHS support real-time notifications?

Yes. 24×7 location monitoring with email and SMS notification support via Adtran Ensemble Fiber Director, helping operations teams respond rapidly to access events.

Is the MHS vulnerable to wireless jamming?

The MHS does not depend on wireless communication or communication protocols at the sensor location. According to the brochure, its passive design therefore eliminates the opportunity to jam the monitoring operation through wireless interference.

What temperature range does the MHS support?

The specified operating temperature range is -20°C to +75°C, supporting deployment across a wide range of environmental conditions.

Does installation require any additional components?

Yes. The MHS does not have an integrated coupler. Installation requires an additional 95/5 coupler, typically spliced into an OSP enclosure near the maintenance hole. The MHS includes a 7-meter fiber-optic cable for connection to the coupler's 5% port.

What MHS variants are available?

Two variants are available based on the mounting/activation distance: 25 mm and 35 mm. Both include a wall-mounting bracket, and optional matching step protectors are available to help protect the sensor when the maintenance hole lid is removed.

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