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モニター Crowcon Gasman IIのPDF 技術説明をオンラインで閲覧またはダウンロードできます。Crowcon Gasman II 18 ページ。 Portable gas detector

Functional Description

The GasmanII Portable Gas Detector system is designed to detect the presence of toxic or flammable gases or the

absence of life supporting gases. As an option it may be fitted with a low power transmitter PCB to permit the use of a

body-worn Vibrating Pager Unit.

The standard GasmanII Portable Gas Detector monitors the level of a particular gas in the atmosphere and provides both

an audible and a visual alarm should the gas levels become unacceptable. When fitted with the optional low power

transmitter PCB the unit also emits a 418MHz RF carrier wave that is 'On-Off-Key' (OOK) modulated at about 10Hz. It is

this signal, which is only emitted while the alarm condition exists, that the GasmanII Vibrating Pager Unit intercepts and

produce a pulsing vibration to augment the audible and visual alarms provided by the GasmanII Portable Gas Detector.

The circuit consists of the functional blocks as shown in Figure 1 below and a complete unit is assembled from 3 PCBs,

with an optional fourth PCB, as shown in the appendices. Each of the three distinct gas types requires a specific type of

gas sensor, signal conditioning circuitry and calibration information. All of the gas sensors share a similar mechanical

design and are plugged into a small daughter board at the top of the unit. The output signal from the various types of

sensor is different and each requires a corresponding signal conditioning amplifier to interface the signal to the common

CPU section. The calibration information is stored in non-volatile memory within the unit and is factory set.

The CPU is powered in a low-power state at all times that batteries are present and controls the electronic switch to apply

power to the rest of the circuitry when one of the front-panel mounted buttons is pressed. Once powered the unit

continuously monitors the gas level comparing it with preset alarm levels and, should an alarm level be exceeded, the

buzzer and the LED operate to provide both audible and visual warnings. The two signals that drive the LEDs are

combined on the optional low-power transmitter PCB to form a 10Hz signal that is used to modulate an RF Monolithics

transmitter module.

electronic

switch

LCD display

buzzer

gas

analogue

cpu

sensor

signal conditioning

(ROM & RAM)

LEDs

low

power

txmtr

(optional)

Figure 1: Gasman II Block Diagram