HOBO
®
U12 4-External Channel Outdoor/Industrial Data Logger
2
4-20mA Input Cable
This cable (part number CABLE-4-20mA) measures current
from 0 to 20.1 mA. Do not expose to current above 20 mA or to
negative current. Do not cut off the end of the gray cable where
it connects to the blue and yellow wires, as it contains the
precision resistor required for current measurement.
If you are using this cable outdoors, you will need to ensure that
the connection to your sensor or device is also weatherproof.
The connection between the gray cable and yellow and blue
wires is splash-proof, but not weatherproof.
Voltage Input Cable
The logger’s external inputs can accept the voltage input cable
(Onset part number CABLE-2.5-STEREO), which allows a
voltage to be recorded. The input line must not be exposed to
signals below 0 V or above 2.5 V.
If you are using this cable outdoors, you will need to ensure that
the connection to your sensor or device is also weatherproof.
Voltage Input Cable Connections
Wire Connection
Red
Switched 2.5 V output
White Voltage
input
Black Ground
Other External Sensors
Onset has a range of external temperature sensors, AC current
sensors, and cables for incorporating other sensors that are
compatible with the U12 4-External Channel Data Logger.
Measurement specifications for using Onset temperature and AC
current sensors with this logger are provided in the sensor
manuals. Visit www.onsetcomp.com for details on compatible
sensors.
Switched 2.5 V Output
The external input channels have a switched 2.5 V output. This
signal can be used to power a sensor directly, or it can be used to
trigger an external circuit. External sensors should draw no more
than 4 mA total when powered.
The switched 2.5 V output turns on about 1 ms before the
external channels are measured
and stays powered for 21 ms
after the external channels are
measured, as shown in the
diagram. The grey area shows
the 16 ms period during which
the logger samples the input
signals.
When using multiple voltage and/or current inputs, the (-) from
your current source(s) and the 0 V line of your voltage source(s)
are tied together at the logger. If these lines are at different
voltage potentials, this may cause inaccurate readings or even
damage your logger.
Keep in mind that these lines may also be tied to earth ground
through your PC interface cable when connected to your
computer. Special precautions may be necessary if any of your
voltage or current source common lines are not tied to earth
ground. Input isolators may be needed in industrial environments
to prevent errors caused by ground loops.
CAUTION:
Analog channel input cannot exceed 2.5
VDC. For sensor outputs up to 10 VDC, use appropriate
voltage adapter cable.
Attaching the Sensors
1.
Remove the white tabs holding the cover on and then
remove the cover.
2.
Using a 15 mm wrench, remove the dome nut for the
channel you wish to connect to.
3.
Pull the exposed end of the black rubber plug to remove it
from the fitting.
Do not throw these plugs away!
These
plugs are needed to maintain a weatherproof seal for
channels that are not connected to sensors or input cables.
4.
Slide the dome nut over the plug end of the cable. The dome
nut’s threads should face towards the case.
5.
Feed the plug end of the cable from the outside of the case
through the dome fitting of the channel you want to use
(refer to label on the logger’s cover) and plug it into the
corresponding port as shown in the diagram. If you have
difficulty inserting the plug through the fitting, a small
amount of dishwashing liquid can be used as a lubricant on
the plug. (Do not use O-ring lubricant.)
6.
Thread the dome nut back onto fitting and hand-tighten it.
Tighten an additional half-turn with a 15 mm wrench.
