3
The display light button is near the rotary switch control. Pushing that button will activate a
backlight on the LCD display which will remain on for 6 seconds. It will only be visible when the
instrument is in a dark area and should not be used excessively because it creates a large drain
on the batteries.
Note:
For best results in moving air, turn the instrument sideways (at 90 deg angle) to the air
flow. Air flow into the sensor will cool it, lowering its temperature, and changing the reading.
CHARGING THE BATTERIES
For the quickest charge (4-5 hours) use a 12-24 VDC adapter, 1 A. A 300 mA adapter, which is
more commonly available, will charge the batteries in about 8 hours (over night). The batteries
should last for 16-24 hours of continuous use (2-3 work days).
CALIBRATION
The A-22 uses a calibration concept that is somewhat novel: The ozone sensor is mounted on a
sensing board, called the SM-X, includes a microprocessor and EEPROM memory. The exact
calibration curve for that particular ozone sensor is burned into the EEPROM. The A-22 host
instrument adjusts the sensor readings for temperature and relative humidity based on data sent
from the sensor module.
In most cases, it is probably cheaper and faster to replace the SM-X sensor board with a freshly
calibrated one than to send the current old one back for recalibration. Also the SM-X board can
NOT be recalibrated in the field. It can only be done by a special computer at Eco Sensors, Inc. It
is more expensive to recalibrate the SM-X than to by a new precalibrated one because the
original SM-Xs are calibrated with semiautomatic equipment.
The SM-X calibration can be checked by the Eco Sensors OG-3 calibration checker. The
calibration is within 15% over the sensor's range. For the OG-3 to mate with the A-22 sensor, it
will be necessary to remove the orange protective “boot” that surrounds and protects the
instrument.
OUTPUTS TO EXTERNAL EQUIPMENT
The A-22 has a variety of outputs to external equipment. Referring to the jacks on the right side
of the instrument, these are:
AC Adaptor USB 2 Circuit output jack:
Tip: 0-2 VDC
Ring: 4-20 mA
