Toxalert Tox-CO/ANA - Manual (Page 2)

BACKGROUND:
The Model Tox-CO/ANA uses the most current techology in sensors and electronics resulting in a stable
and long life unit. The heart of the electronics is a microprocessor with 12 bit analog input resolution and
8 bit analog output resolution.
The Model Tox-CO/ANA uses tin oxide semiconductor technology for carbon monoxide sensing. These
sensors are internally heated to sense gas. In the Model Tox-CO/ANA the heater is microprocessor
cycled to enhance the detection of carbon monoxide over other background gases. Readings are taken
every two and one half minutes at the end of heating cycle. Then the sensor is heated to a higher tem-
perature for self cleaning. After the cleaning phase, the sensor is returned to the sensing temperature.
The heater current is microprocessor controlled and monitored to compensate for any long term drift in
the sensors internal parameters to ensure long term stability and repeatability of readings.
Since the tin oxide technology sensor is sensitive to the ambient gas temperature and humidity, compen-
sation for gas temperature and humidity are included in the operating software of the microprocessor.
Factory calibration is performed in a triple point technique, at 50, 200 and 400 ppm of carbon monixide
concentrations with normal temperature and humidity. The software in the Model Tox-CO/ANA auto-
matically compensates the output signal for changes in ambient relative humidity and temperature. Cali-
bration can be checked at any time by using the optional field calibration check kit. This kit utilizes a
known CO gas sample.
The microprocessor system includes self diagnostic, self restarting, and remote failure reporting. The
self diagnostics allow the microprocessor to determine that the entire software code is 100% intact upon
power up and at other periodic intervals. If there were a failure in the code, the model Tox-CO/ANA will
lower the output signal below 4 milliamps to signal the controller using the signal that maintenance is
required. The same lowering of the output signal occurs should the microprocessor determine a failure in
any other components in the system including the carbon monoxide sensor itself. In the event that a
severe electrical disturbance occurs that caused the Model Tox-CO/ANA to malfunction, the micropro-
cessor will restart without human intervention, and if all code is found to be intact, will resume normal
operation. The Model Tox-CO/ANA is also tolerant of power line transients.
The Model Tox-CO/ANA shows its operating status with several LED (light emitting diode) indicators.
Indicators used are: +5V power on, +15V power on, system operating normally, and system in calibra-
tion.
The Model Tox-CO/ANA is designed for easy installation. The electronics and sensor are removable
from the cabinet as one unit for easy shipping and installation. The Tox-CO/ANA is mounted in a metal
cabinet with a hinged, key locking door.
Codes require that the ventilation fans run continuously in enclosed parking areas unless a carbon
monoxide monitoring system is employed to control the fans.
Uniform Building Code Section 705 - In all parking garages, other than open parking
garages as defined in Section 709 (b), used for storing or handling of automobiles operat-
ing under their own power and on all loading platforms in bus terminals, ventilation shall
be provided capable of exhausting a minimum of 1.5 cfm per square foot of gross floor
area. The building official may approve an alternate ventilation system designed to ex-
haust a minimum of 14,000 cfm for each operating vehicle. Such system shall be based
upon the anticipated instantaneous movement rate of vehicles but not less than 2.5 percent
(or on vehicle) of the garage capacity.
Automatic CO sensing devices may be employed to modulate the ventilation sys-
tem to maintain a maximum average concentration of CO of 35 ppm during any
eight-hour period, with a maximum concentration no greater than 200 ppm for a
period not exceeding one hour.
PRODUCT DESCRIPTION:
Therefore, especially in colder climates, it is advantageous to install a CO system. Not only would a sav-
ings occur merely in the power needed to run the fans, but also, limiting the introduction of cold make-
up air will reduce the overall heating (and in some cases cooling) requirements.