7
DATA INTERPRETATION
2.3 HEATER POWER SUPPLY
Apogee oxygen sensors are equipped with an internal resistance heater. The heater is
designed to maintain the temperature of the sensing element at approximately 2 °C above
ambient temperature in condensing (100% relative humidity) environments (e.g., soil).
Heating the sensing element keeps condensation from forming on the membrane, which
would block the oxygen diffusion path and result in artificially low oxygen measurements
for an extended period of time. To operate the heater, a continuous 12-VDC supply should be
attached to the heater leads.
Apogee oxygen sensors purchased from METER for use with METER ZENTRA series data
loggers come with a special cable addition that splits the sensor cable into a stereo
connector that connects to the data logger and a separate heater cable. A continuous
12-VDC supply should be applied across the red (positive) and black (negative) leads of this
heater cable.
If mains power is available, the 12-VDC supply can be a simple “wall wart”. If mains power
is unavailable, a 12-V battery is appropriate and a solar panel and charge controller can be
used to maintain battery charge. Under most conditions, a small battery (7 A
· h) with a 5-W
solar panel is sufficient to heat multiple oxygen sensors. There are many battery, charge
controller, and solar panel options available online and from local retailers.
3. DATA INTERPRETATION
Apogee oxygen sensors used with the ZENTRA system report gaseous oxygen concentration
in units of percent (%) and the internal sensor temperature in units that are configurable by
the user.
4. TROUBLESHOOTING
This troubleshooting section details possible major problems and their solutions. If the
problem is not listed or these solutions do not solve the issue, contact
Table 2 Troubleshooting
Problem
Possible Solution
Sensor not responding
Check power to the sensor and logger.
Check sensor cable and stereo plug connector integrity.
Check that the SDI-12 address of the sensor is
0
(factory default).
Check this with ZENTRA Utility by going to Actions, select Digital
sensor terminal, choose the port that sensor is on, and send the
?I!
command to the sensor from the dropdown menu.
