家用气体报警器模块

preliminary
the board is a microprocessor based application, designed for gas sensing applications, for use with either 3-electrode electrochemical cells or catalytic gas sensors.
the raw signal input from the sensor is processed digitally by the microprocessor, which also stores information like calibration data, the range and lifetime of the sensor. remora® can be interrogated digitally, with information such as alarm thresholds, fault conditions,calibration information etc., being available from the microprocessor’s registries.
remora® is available in various versions and options, depending on the gas sensor with which is being used and the application. it is primarily designed to compliment the nemoto range of gas sensors for residential gas detection applications and can be used as a sensing platform within a residential gas detector product.
board structure
remora® is built around a 12bit microcontroller. it provides analog outputs and a serial output rx/tx to facilitate communication.
a number of versions of the device are available, depending on the gas sensor with which is being used:
- catalytic sensor (nemoto type nap-50a) for combustible gases detection;
- electrochemical cell (nemoto type nap-505) for carbon monoxide detection.
various circuits are implemented in accordance with the sensor used and the application:
- the self test circuit (for the co cell)
- zero drift compensation circuit.
- a special version is available or carbon dioxide (co2) detection, using optoacoustic technology
board operation
the pcb is provided with some basic information written in the  icroprocessor’s memory:
- lot/serial number
- calibration date
- span factor (for catalytic sensor)
- alarm thresholds
all the above are written in the registries and are available for reading on the digital output.
other output data available:
- the present measured gas concentration on demand (in ppm or%lel depending on the application and sensor used)
- alarm condition
- fault condition
- the age of the sensor (depending on the application)
according to the board version, through the respective protocol, all the above information is available for readout.
notes:
1. span/rank - for a catalytic sensor monitoring combustibele gases, the relative response of the target gas is used to determine the range of the device. the readout drift in gas is memorized as the span, together with the zero value when calibrating the device.
when used with nap-505 co sensor, a rank se-lection gives the drift in na/1ppm of co detected.
the span or rank respectively, depending on the application, is memorized in the microprocessor’s registries.
2. lifetime - usually the lifetime of the electrochemical cell nap-505 is around 5 years, provided the signal level of the cell does not fall bellow 40% of the original output. the microprocessor software is provided with a timer, which monitors the time elapsed from the sensor’s first calibration. a fault signal is to be provided on the serial output after the 5 years, stating that the sensor should be replaced.
3. auto-zero – the drift of the zero indication in time affects the indication of the actual gas level so it is automatically compensated. the software implemented contains a routine which compensates for the drift in zero level.
4. self-test – for co electrochemical cells, as defined by various standards, a self-test routine is included, which monitors the sensor’se-lectrodes for short or open circuit faults. the microprocessor will indicate a short or open circuit by means of the on-board fault signal. also, in case of electrolyte leakage in significant quantity or in case of complete drying out of electrolyte, the self test will activate a fault output to warn the imminent failure of the cell.
5. ack/peak – an input is provided instead of alarm 2 to acknowledge the alarm signal if requested, or to provide the peak concentration level from the last acknowledgement on.
6. buzzer – an output is provided instead of alarm 1 for a buzzer if necessary.
pin desc-ription


annex 1 – block scheme