HOBO U23 Pro v2 Temperature/Relative Humidity Data Logger - U23-001

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IMPORTANT: This HOBO data logger requires HOBOware software and a communications device. See compatible items below.


The HOBO Pro v2 Temperature/Relative Humidity data logger is a weatherproof data logger with built-in temperature and relative humidity sensors. The Relative Humidity sensor provides superior durability in humid environments and is user-replaceable.

Optical Interface for data transfer





  • Weatherproof housing for use in outdoor or condensing environments
  • High accuracy
  • Replaceable Relative Humidity sensor provides fast response and superior recovery from condensing conditions
  • Small-diameter external sensor versions for measurements in tight spaces
  • Optic USB interface for fast and reliable download
  • Compatible with HOBOware and HOBOware Pro software for logger setup, graphing and analysis

The U23-001 Data Logger is for use in Outdoor environments

The U23-001 Data Logger supports the following measurements:

Temperature, Relative Humidity

Onset # U23-001
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HOBO U23 Pro v2 Temperature/Relative Humidity Data Loggers

Temperature Sensor
Operation range Internal sensors: -40° to 70°C (-40° to 158°F)
U23-002 external temperature sensor: -40° to 70°C (-40° to 158°F)
U23-003 and U23-004 external sensors: -40° to 100°C (-40° to 212°F), with tip and cable immersion in fresh water up to 50°C (122°F) for one year

Accuracy: ±0.21°C from 0° to 50°C (±0.38°F from 32° to 122°F); see Plot A
Resolution: 0.02°C at 25°C (0.04°F at 77°F); see Plot A

Plot A and Plot BResponse time
(typical to 90%)
U23-001 Internal sensor: 40 minutes in air moving 1 m/sec
U23-002 external temperature sensor: 5 minutes in air moving 1 m/sec
U23-003 and U23-004 external sensors: 3 minutes in air moving 1 m/sec; 30 seconds in stirred water

Stability (drift): < 0.1°C (0.18°F) per year

Relative Humidity Sensor (U23-001, U23-002 only)
Operation range 0-100% RH, -40° to 70°C (-40° to 158°F) Exposure to conditions below -20°C (-4°F)
or above 95%
RH may temporarily increase the maximum RH sensor error by an additional 1%

Accuracy: ±2.5% from 10% to 90% RH (typical), to a maximum of ±3.5% including hysteresis. See Plot B for full range.

Resolution: 0.03%

Response time
(typical to 90%)
U23-001: 40 minute in air moving 1 m/sec with protective cap
U23-002: 5 minutes in air moving 1 m/sec with protective cap

Stability (drift) < 1% per year typical

Operation range -40° to 70°C (-40° to 158°F)
Real-time clock ± 1 minute per month 0° to 50°C (32° to 122°F)
Battery 1/2 AA, 3.6 Volt lithium, user-replaceable (part # HP-B)

Battery life (typical use): 3 years with 1 minute or greater logging interval

Memory (non-volatile): 64K bytes memory (approx. 21,000 temperature and RH measurements)

Materials All models:
ASA styrene polymer housing and mounting clamp; polypropylene protective cap; Buna-N o-ring(s)
U23-001, U23-002 only: ASA styrene polymer RH sensor cap; modified hydrophobic polyethersulfone membrane

U23-001: No cables
U23-002: One 184 cm (6 ft.) PVC cable; sensor diameter 1 cm (0.38 in.)
U23-003: Two 184 cm (6 ft.) PVC cables; sensor diameter 0.5 cm (0.20 in.)
U23-004: One 184 cm (6 ft.) PVC cable; sensor diameter 0.5 cm (0.20 in.)

Environmental rating: Electronics housing is NEMA 6P equivalent (tolerant of brief submergence)
Units with RH sensors are NEMA 4 equivalent (splash-resistant)

Launch modes: Immediate start; delayed start

Logging interval: Fixed-rate or multiple logging intervals, with up to 8 user-defined logging intervals and durations; logging intervals from 1 second to 18 hours (refer to HOBOware software manual)

Offload modes: Offload while logging; stop and offload

Battery indication: Battery voltage can be viewed in status screen and optionally logged in datafile. Low battery indication in datafile.

U23-001: 57 g (1.5 oz)
U23-002: 118 g (3.1 oz)
U23-003: 138 g (3.7 oz)
U23-004: 102 g (2.7 oz)

Dimensions: Housing measures 10.2 × 3.8 cm (4.0 × 1.5 in.)

NIST certificate Temperature certificate available for additional charge

The CE Marking identifies this product as complying with the relevant directives in the European Union (EU).

Part Number
Graphing and Analysis
HOBOware Pro Mac/Win (USB cable included)
HOBOware Pro - Mac/Win Data Logger Software - Download Only
Part Number
Data Offload - Base Stations - Shuttles
Optic USB Base Station
HOBO® Waterproof Shuttle
Part Number
Replacement battery for U23 data loggers (sold individually)
Small Desiccant Pack (25-count)
Replacement RH Sensor
Replacement Relative Humidity Sensor for U23-001
Part Number
Carrying Case
Pelican Case
Compliance Certificate
Compliance Certificate
Data Offload Couplers
Replacement Coupler for HOBO Pro v2
Mounting Accessories
Clamp Kit for U23-001
NIST Certification
Setup Charge for NIST Traceable Certification
Please call 1-800-564-4377 to place an order.
NIST testing usually takes between 1-2 weeks.
NIST Temperature point certification
Please call 1-800-564-4377 to place an order. NIST testing usually takes between 1-2 weeks.
Solar Radiation Shield
Solar Radiation Shield (assembled)
Solar Radiation Shield
UV Protection Caps
UV Protection Caps for U23 Series Data Loggers
Documentation for the U23-001

Growing-Degree-Days-Assistant-Users-Guide-10574 logo
HOBOware® Growing Degree Days Assistant White Paper

Replacement Battery Kit for U23 Data Loggers - HP-B

15932-B-Testing-Sensirion-RH-Sensors-White-Paper logo
Testing Sensirion RH Sensors - White Paper - This white paper explains the recommended procedure for testing the accuracy of Sensirion relative humidity sensors in HOBO data loggers and sensors (models U12‐011, U14‐001, U23‐001, ZW‐003, ZW‐005, ZW‐007, UX100-011, and smart sensor S‐THB‐M002 compatible with several loggers).

U23-00x Manual

The following are associated resources for this product. In general users of this product can gain insight into its possible use by utilizing the resources below.