How to Choose the Right Data Logger for Temperature and Humidity Monitoring

In conservation, climate is everything. Few variables have as much impact on the condition of artworks, documents and artefacts as temperature and relative humidity: repeated fluctuations, undetected peaks or excessively humid environments are responsible for a large proportion of deterioration. Continuous monitoring is not an optional extra—it is the foundation of preventive conservation.

This requires data loggers: compact instruments that record temperature and RH over time and can be placed inside display cases, storage areas, cabinets or exhibition rooms. CTS offers five dual-channel models (temperature + humidity), all reliable but designed for different requirements. The first question should not be “Which one is the best?” but rather “How do I want to view and download the data?” Almost every other choice follows from this.

If the instrument is within easy reach. Direct-USB models (EL-USB-2 and EL-USB-2 LCD) are the simplest and most cost-effective: they plug directly into a computer’s USB port, with no cables or accessories required. The LCD version also includes a display for checking current, minimum and maximum values on site. They are ideal for display cases and storage areas where the logger can easily be retrieved. Please note that the sensor is sensitive to chemical vapours.

If you need large memory capacity and high accuracy. The HOBO UX100-003 downloads data via USB cable and offers the largest memory capacity—more than 84,000 readings—with logging intervals as short as 1 second and excellent temperature accuracy (±0.21°C). It is a robust solution suitable for fixed monitoring stations and transport applications.

If you do not want to open the display case. The HOBO MX1101 communicates via Bluetooth, allowing data to be downloaded remotely using a smartphone without moving the instrument or opening the display case. It also calculates the dew point. The HOBOmobile app is free; however, HOBOware software, sold separately, is required for more advanced analysis.

If continuous monitoring and alarms are required. The EL-WiFi-TH is the only model that provides real-time monitoring: data is automatically uploaded to the cloud, can be accessed from any device and can trigger email alerts when set thresholds are exceeded. It is ideal for critical environments. However, it requires Wi-Fi coverage and has a shorter battery life—or must be connected to mains power. If the Wi-Fi connection is lost, it continues recording data in its internal memory and synchronises automatically once the connection is restored.

General precautions for all models. None of these instruments is waterproof, so they must be protected from water and condensation. Battery life varies considerably—from 2–3 years for the EL-USB models to approximately 6 months for the Wi-Fi model—so batteries should be replaced before any critical monitoring campaign.

In summary

EL-USB-2 — Direct USB connection

Suitable when the instrument can be easily retrieved and an economical solution is required for multiple monitoring points.

• Museum storage area: several units distributed among shelving and cabinets, with data downloaded in rotation during routine inspections.
• Basic monitoring of an exhibition room: continuous temperature and RH recording at low cost, with monthly checks via computer.
• Large-scale monitoring campaigns: when many rooms need to be equipped on a limited budget, this model allows the greatest number of monitoring points.
• Pre-restoration environmental assessment: the logger can be left in place for several weeks to provide an overview of climatic conditions before work begins.

EL-USB-2 LCD — Direct USB connection + display

As above, but designed for situations where readings need to be checked on site without using a computer.

• Display case monitored by gallery staff: personnel can check temperature, RH and minimum/maximum values at a glance during routine inspections.
• Public exhibition room: rapid verification of environmental conditions before opening to visitors.
• Frequently accessed storage area: anyone entering can immediately check the current conditions without downloading the data.
• Training sessions and site surveys: useful for displaying current readings directly beside the artwork.

HOBO UX100-003 — USB cable

For users who need high time resolution, large memory capacity and high temperature accuracy.

• Transport and artwork loans: logging intervals as short as 1 second and ample memory make it possible to record every stage of a journey without interruption, including long-distance transport.
• Detailed thermal studies: fine analysis of temperature changes inside display cases or near heat sources such as spotlights or exposed walls.
• Fixed laboratory monitoring station: long-term, high-frequency data recording with scheduled downloads to a computer.
• Microclimate assessment: suitable when dense datasets are required to identify rapid fluctuations that longer logging intervals could miss.

HOBO MX1101 — Bluetooth

For situations where opening the display case or physically reaching the instrument would be difficult.

• Sealed display cases and enclosed microclimates: data can be downloaded by smartphone without breaking the seal or altering the internal environment.
• Hard-to-reach or elevated locations: instruments positioned high up or behind artworks can be read remotely.
• Churches and historic interiors: discreet monitoring without cables or invasive alterations to the installation.
• Dew-point monitoring: suitable where the risk of condensation must be assessed directly, such as near cold walls or in damp environments.

EL-WiFi-TH — Wi-Fi/cloud

For continuous monitoring of critical environments with immediate alerts.

• Storage areas containing high-value collections: email alerts when thresholds are exceeded allow action to be taken before damage occurs.
• Rooms with climate-control systems: real-time verification that environmental conditions remain within the required parameters.
• Centralised management of multiple environments: several sensors located in different rooms or buildings can be monitored from a single account—particularly useful for museum networks.
• Sensitive periods when no staff are present: during holidays, closures or overnight periods, the environment remains monitored remotely.
• Incoming loans: cloud-based data can be used to demonstrate to lenders that the agreed environmental conditions are being maintained.