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Specifications subject to change without notice. | Tox_D_1119, Ex_D_1119, CO2_D_0320 | USA 200413 | Page 3 of 17
SC2-AT6 – UserManual
Intended Use
The SC2 sensors are designed for the measurement of toxic gases and oxygen in a wide range of applications with
the PolyGard
®
2 Series. The AT6 sensor/transmitter operates with 24 VDC and outputs an analog 4-20 mA standard
signal. Both the SC2 sensor cartridge and AT6 sensor/transmitter utilizes similar technologies and thus collective
referred to as same (“sensor cartridge”,”sensors”) in this document unless otherwise noted.
The sensors must not be used in potentially explosive atmospheres. They must only be employed in areas within the
environmental conditions as specified in the Technical Data.
1 Functional Description
1.1 General
The SC2 sensor includes a microprocessor for measurement value processing in addition to the gas sensor element
and the measuring amplifier. All data and measured values of the sensor element are stored in a fail- safe way in the
microprocessor and are digitally transferred via the local bus to the PG2 devices. The calibration management is also
integrated in the microprocessor of the sensor cartridge.
The AT6 sensor/transmitter works according to the same principle as the SC2 series with the exception that the AT6
outputs an analog signal of 4-20 mA (2-10 V as an option).
1.2 Measuring Mode
See description on datasheet for the specific PG2 device.
1.3 Special Mode
See description on datasheet for the specific PG2 device.
1.4 Sensor Element for Toxic Gases and Oxygen
The sensor element is a sealed electro-chemical cell with three electrodes, sensing, reference and counter or with two
electrodes, sensing and reference. The ambient air to be monitored diffuses through a membrane filter into the liquid
electrolyte of the sensor. The chemical process of the measurement is one of oxidation where one molecule of the
target gas is exchanged for one molecule of oxygen. The reaction drives the oxygen molecule to the counter electrode,
generating a DC microampere signal between the sensing and reference electrodes. This signal is linear to the volume
concentration of the sensed gas. The signal is evaluated by the connected amplifier and transformed into a linear
output signal.
Electrochemical processes always lead by-and-by to a loss of sensitivity. Therefore regular calibration of zero- point
and gain is necessary. See section 5.
There is a small quantity of corrosive liquid in the sensor element. If in case of damage persons or
objects touch the liquid, clean the affected areas immediately and carefully as possible with tap water.
Out of use sensors must be disposed in the same way as batteries.
Certain substances and gases in the ambient air to be monitored can affect the sensitivity of the sensor element or
destroy the sensor completely. This is considered sensor poisoning.
The following are currently known:
• Polymerizing substances, such as ethylene oxide, acrylonitrile, butadiene, styrene, silicone.
• Corrosive substances, such as halogenated hydrocarbons.
• Catalytic poisons, such as sulfur and phosphor compounds, silicon compounds, metal vapors.