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HOBO

®

 U12 Temp/RH/Light/ 

External Data Logger 
(Part # U12-012) 

© 2003, 2004 Onset Computer Corporation 
Part #: MAN-U12-012, Doc #: 7661-B 

Inside this package: 

 

HOBO U12 Temp/RH/ 
Light/External Data Logger 

 

Mounting kit with magnet, hook 
and loop tape, tie-wrap mount, 
tie wrap, and two screws. 

 
 
 
Doc # 7661-B, MAN-U12-012 
Onset Computer Corporation 

Thank you for purchasing a HOBO data logger. With proper care, it 
will give you years of accurate and reliable measurements. 

The HOBO U12 Temperature/Relative Humidity/Light/External Data 
Logger is a four-channel logger with 12-bit resolution and can record 
up to 43,000 measurements or events. The external channel accepts a 
variety of sensors, including temperature, and split-core AC current 
sensors as well as 4-20 mA and voltage input cables (sold separately). 
The logger uses a direct USB interface for launching and data readout 
by a computer. 

An Onset software starter kit is required for logger operation. Visit 
www.onsetcomp.com for compatible software.

 

 

Specifications 

Measurement 
range 

Temperature: -20° to 70°C (-4° to 158°F) 
RH: 5% to 95% RH 
Light intensity: 1 to 3000 footcandles (lumens/ft

2

) typical; 

maximum value varies from 1500 to 4500 footcandles 
(lumens/ft

2

External input channel (see sensor manual): 0 to 2.5 DC Volts 

Accuracy 

Temperature: ± 0.35°C from 0° to 50°C (± 0.63°F from 32° to 
122°F), see Plot A 
RH: ± 2.5% from 10 to 90%, see Plot B; conditions above 
80% RH and 60°C (140°F) may cause additional error 
Light intensity: Designed for indoor measurement of relative 
light levels, see Plot D for light wavelength response 
External input channel (see sensor manual): ± 2 mV ± 2.5% of 
absolute reading 

Resolution 

Temperature: 0.03°C at 25°C (0.05°F at 77°F), see Plot A 
RH: 0.03% RH 

Drift 

Temperature: 0.1°C/year (0.2°F/year) 
RH: <1% per year typical; RH hysteresis 1% 

Response time 
in airflow of 1 
m/s (2.2 mph) 

Temperature: 6 minutes, typical to 90% 
RH: 1 minute, typical to 90% 

Time accuracy 

± 1 minute per month at 25°C (77°F), see Plot C 

Operating 
temperature 

Logging: -20° to 70°C (-4° to 158°F) 
Launch/readout: 0° to 50°C (32° to 122°F), per USB 
specification 

Battery life 

1 year typical use 

Memory 

64K bytes (43,000 12-bit measurements) 

Weight 

46 g (1.6 oz) 

Dimensions 

58 x 74 x 22 mm (2.3 x 2.9 x 0.9 inches) 

 

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

 

 

 

Plot A 

Plot B 

 

 

Plot C 

Plot D 

Connecting the logger 

The U-Family logger requires an Onset-supplied USB interface cable to 
connect to the computer. If possible, avoid connecting at temperatures 
below 0°C (32°F)

 

or above 50°C (122°F).

 

1.  Plug the large end of the USB interface cable into a USB port on the 

computer. 

2.  Plug the small end of the USB interface cable into the bottom of the 

logger as shown in the following diagram. 

 

If the logger has never been connected to the computer before, it may take 
a few seconds for the new hardware to be detected. Use the logger 
software to launch and read out the logger.  

Important: If you configure the logger to start with a button start, be 
sure to press and hold down the button on the front of the logger for 
at least three seconds when you want to begin logging.

 

If using an external sensor, be sure to plug it into the side of the logger 
before logging begins. Also select the correct sensor and activate the 
external channel in the logger software when configuring the launch. 

Important: If you select an external channel, but do not plug the 
probe in, false data will be recorded for that channel. 

You can read out the logger while it continues to log, stop it manually 
with the software, or let it record data until the memory is full. 

Refer to the software user’s guide for complete details on launching, 
reading out, and viewing data from the logger. 

Sample and event logging 

The logger can record two types of data: samples and events. Samples are 
the sensor measurements recorded at each logging interval (for example, 
the temperature every minute). Events are independent occurrences 
triggered by a logger activity. Examples of events recorded 
asynchronously during deployment include when the logger is connected 
to the host, when the battery is low, the end of a data file once the logger 
is stopped, and button pushes. 

Press the button on the front of the logger for one second to record an 
event. Both a button up and down event will be recorded. This is useful if 
you want to mark the datafile at a particular point. For example, if the 
logger is located in an incubator, you might press the button each time the 
door is opened.  

The logger stores 64K of data, and can record up to 43,000 samples and 
events combined.  

Using external sensors 

The external input channel has a switched 2.5 V output. This signal can be 
used to power a sensor directly or it can also be used to trigger an external 
circuit. An external sensor should draw no more than 4 mA total when 
powered. The switched 2.5 V output turns on about 15 ms before the 
external channel is measured and stays powered for 48 ms after it is 
measured, as shown in the following diagram. The striped bar shows the 
16 ms period during which the logger samples the input signal. 

 

15 ms 

16 ms 

48 ms 

Important:

 Press this 

button for 

3 seconds

 

when logger is 
launched with Button 
Start or press for 

second

 to record an 

event while logging 

USB interface 
cable plugged 
into logger 

Light 
intensity 
sensor 

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