The SITE-LOG LRHT-3 is a compact 2-channel, battery-powered, standalone data logger designed for accurate monitoring of relative humidity and temperature using an external 3-foot sensor probe.

The logger provides:

• 1 relative humidity channel
• 1 temperature channel
• External 3-foot digital temperature and RH sensor probe
• 8 MB non-volatile flash memory
• USB and TTL-level serial communication
• Configurable alarm and excitation-control outputs
• Long-term standalone data logging

The external sensor probe allows temperature and relative humidity to be measured away from the logger enclosure, making the LRHT-3 particularly useful where the sensing location is difficult to reach or where the logger electronics should remain outside the monitored space.

The aluminum enclosure and conformally coated PCB provide additional protection for industrial, laboratory, and field applications.

Relative Humidity and Temperature Measurement

The LRHT-3 simultaneously measures:

• Relative Humidity: 0–100% RH
• Temperature: −40°C to +70°C (−40°F to +158°F)

Published measurement accuracy is:

• Temperature: ±0.2°C at 25°C
• Relative Humidity: ±2% RH from 20% to 80% RH

The high-accuracy digital sensor makes the LRHT-3 suitable for environmental, laboratory, research, storage, HVAC, and other applications where temperature and humidity must be monitored together.

External Temperature and Humidity Sensor Probe

Unlike the LRHT-1, which uses an internal sensor, the LRHT-3 uses an external 3-foot temperature and relative-humidity sensor probe.

The probe connects to the logger through a terminal-block connector and allows the sensing element to be positioned separately from the logger enclosure.

This configuration is useful for applications such as:

• Environmental chambers
• Incubators
• Cabinets and enclosures
• Storage areas
• HVAC ducts
• Equipment compartments
• Laboratory test setups
• Locations where the logger should remain outside the monitored environment

The LRHT-3 uses a Sensirion digital relative-humidity sensor. 

Standalone Operation and Long-Term Recording

The LRHT-3 operates independently after configuration and stores measurements in 8 MB of non-volatile flash memory.

The memory provides storage for approximately 4 million readings and retains recorded data for more than 20 years.

Logging can be configured for:

• Immediate start
• Delayed start
• Field push-button activation

When memory becomes full, the logger can either:

• Stop recording, or
• Continue recording in FIFO mode

The built-in 3.6 V lithium battery provides up to approximately 10 years of operation at a 1-minute sampling interval, depending on operating conditions and configuration. 

USB Communication and SiteView Software

The LRHT-3 connects directly to a Windows PC through its Plug & Play USB interface.

SiteView software provides tools for:

• Logger configuration
• Data download
• Real-time temperature and humidity viewing
• Graphing
• Alarm configuration
• Custom calibration
• Custom equations
• Data analysis

The logger also includes an AUX RJ11 interface for TTL-level serial communication.

USB and AUX communication support automatic baud-rate detection from:

2400 to 115200 bps.

Alarm and Excitation Control

The LRHT-3 provides configurable alarm and control functions for applications requiring more than basic data recording.

Each channel supports two programmable alarm thresholds.

The available output terminals can be configured for:

• Alarm output
• Excitation control

The onboard status LED provides visual indication of normal sampling, alarm conditions, and low battery status. 

Remote Access and Network Integration

Although the LRHT-3 is a USB-based data logger, it can also be accessed remotely over an Ethernet network by connecting it to a Microedge Smart-Hub.

Smart-Hub acts as a communication gateway and allows connected USB data loggers to be accessed through:

• SiteView
• SiteView-Web
• SiteView SDK
• Pluto

Smart-Hub also provides:

• RESTful Web API
• Modbus TCP Gateway

This allows LRHT-3 temperature and relative-humidity data to be integrated with third-party software, PLCs, HMIs, SCADA systems, building-management systems, and other industrial monitoring platforms.

Rugged Industrial Design

The LRHT-3 is housed in a durable aluminum enclosure.

The PCB is conformally coated to provide additional protection against moisture, corrosion, and mildew.

Its operating environment is:

−40°C to +70°C (−40°F to +158°F)

and:

0–95% RH, non-condensing. 

KEY FEATURES

• Relative Humidity and Temperature Measurement
  Simultaneously records RH and temperature.

• External 3-Foot Sensor Probe
  Allows temperature and humidity to be measured away from the logger enclosure.

• Sensirion Digital RH Sensor

• 0–100% RH Measurement Range

• −40°C to +70°C Temperature Range

• High Temperature Accuracy
  ±0.2°C at 25°C.

• High Relative Humidity Accuracy
  ±2% RH from 20% to 80% RH.

• 8 MB Non-Volatile Flash Memory
  Stores approximately 4 million readings.

• 1 Second to 12 Hour Sampling
  External power is required when the sampling interval is less than 5 seconds.

• Up to 10 Years Battery Life
  Based on a 1-minute sampling interval.

• USB Communication

• TTL-Level Serial Communication
  AUX RJ11 interface with automatic baud-rate detection from 2400 to 115200 bps.

• SiteView Software Support

• Programmable Alarm Thresholds

• Alarm Output and Excitation Control

• Remote Network Access through Smart-Hub

• RESTful Web API through Smart-Hub

• Modbus TCP Gateway through Smart-Hub

• Rugged Aluminum Enclosure

• Conformally Coated PCB

  
  

TYPICAL APPLICATIONS

The LRHT-3 is suitable for:

• Laboratory temperature and humidity monitoring
• Environmental chambers
• Storage facilities
• Warehouses
• HVAC monitoring
• Equipment enclosures
• Cabinets and controlled spaces
• Incubators
• Research
• Product testing
• Manufacturing environments
• Museum and archive monitoring
• Building environmental monitoring
• Long-term temperature and humidity logging
• Remote environmental monitoring through Smart-Hub

DOCUMENTS

• SITE-LOG Relative Humidity Data Logger (LRHT-3) Specifications
• SiteView Specifications