초록 ▼

An operational amplifier (34) has its inverting input connected to a electrochemical gas sensor (38) for amplifying the current produced thereby in response to presence of a predetermined gas. In order to determine whether a sensor (38) is indeed present and that a sensor present is serviceable, a t

An operational amplifier (34) has its inverting input connected to a electrochemical gas sensor (38) for amplifying the current produced thereby in response to presence of a predetermined gas. In order to determine whether a sensor (38) is indeed present and that a sensor present is serviceable, a transient is applied to the non-inverting input of the operation amplifier (34). The presence or absence of the sensor (38) alters the transfer function of the operational amplifier (34) in respect of the test signal. If a serviceable sensor (38) is present, the gain of the operational amplifier (34) is high for the transient resulting at square pulse output. However, if a serviceable sensor (38) is not present, the gain of the operational amplifier (34) is relatively low and the transient retains its original form. Consequently the presence of a serviceable sensor (38) can be determined from the output of the operational amplifier (34) in response to the transient test signal.

대표청구항 ▼

[ What is claimed is:] [1.]1. A self-testing gas detecting apparatus comprising an electricalinterconnection for making a connection to an electrochemical gas sensor, a test signal generating circuit for generating a test signal which comprises a transient, an amplifier for processing the test signa

[ What is claimed is:] [1.]1. A self-testing gas detecting apparatus comprising an electricalinterconnection for making a connection to an electrochemical gas sensor, a test signal generating circuit for generating a test signal which comprises a transient, an amplifier for processing the test signal from the test signal generating circuit according to a transfer function, and a signalling device, said interconnection being arranged for connecting an electrochemical gas sensor as a component of the amplifier so as to determine said transfer function, wherein the signalling device is responsive to the processed test signal output by the amplifier to signal a fault condition if the processed test signal is not indicative of a serviceable electrochemical gas sensor being connnected into the amplifying circuit by said interconnection.