Prime2
Voltage output Infrared Gas Sensor for Carbon Dioxide

Description and Operation

The Prime2 sensor use the non-dispersive infrared method to detect the presence of carbon dioxide. The sensor contains an infrared radiation source, a dual element infrared detector, a unique optical waveguide into which gas diffuses and integrated ARM7 core microprocessor based electronics to provide a voltage output which isindependent of the power supply polarity. The sensor can be configured to provide a linear voltage output, typically 0.4V 2.0V over range with respect to the negative supply pin, or a pellistor format output, typically mid supply at zero with the voltage output increasing with respect to the detector pin by 100mV at range. In addition, the output can be read and the internal configuration can be accessed by a serial communications link. The communication link contacts are pads in the 3 pin version Prime2 and pins in the 5 pin version Prime2. The internal electronics perform all the functions of driving the optical parts of the sensor, extracting the detector signals, converting the signals to a concentration, applying temperature compensation and scaling the output. When in a pellistor configuration, the Prime2 can operate in existing pellistor circuitry subject to the power supply requirements. External components will be required to meet the power supply requirement when a Prime2 is used in constant current pellistor circuitry. The Prime2 is not currently Ex-approved so should be housed in a suitable Ex enclosure when used in Hazardous areas.

Features

Operates independent of supply polarity

Voltage or pellistor mimic bridge output

Operating voltage range 3.0V 5.0V

Operating current 80mA typical

Latest technology MEMS detectors

Sensing ranges: 0-5000ppm CO2 up to 0-10%volume CO2

All metal construction with isolated housing

Small internal volume

Flexible electronic configuration access

User calibration also enabled by hardware connections

Wide operating temperature range

Fast response

Temperature Compensation

The Prime2 is temperature compensated for both zero and span at the calibration gas concentration level.

Sensor Warmup

When power is first applied or when a reset has occurred or during recovery from a fault condition the Prime2 outputs 1.56% of scale (0.375V in voltage mode or 1.56mV in pellistor mode) for 5 seconds then outputs 0% of scale for a warmup period (default is 15 seconds). After this time the output follows the extracted gas value.

Fault Indication

The Prime2 continuously monitors several internal parameters to ensure that the internal hardware and software are operating correctly. If a fault condition is detected then the output is set to 0V in the case of a voltage output(equivalent to 25% FSD for a 4mA zero) or to approximately 200% scale in pellistor output, emulating a partly open compensator. Some faults are recoverable (e.g. a brown-out in incoming supply voltage) and the Prime2 continuously checks for possible recovery. If a fault can be recovered from then the output follows the sensor warmup sequence before following the extracted gas value.