| CPC A61M 16/161 (2014.02) [A61M 16/109 (2014.02); A61M 16/162 (2013.01); A61M 2205/3382 (2013.01); A61M 2205/3386 (2013.01); A61M 2205/35 (2013.01)] | 17 Claims |

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1. A sensor comprising:
a transmitter for emitting an electromagnetic radiation signal;
a receiver for receiving the electromagnetic radiation signal and providing an output signal indicative of a received amount of electromagnetic radiation at the receiver; and
a controller configured to:
vary an intensity of the electromagnetic radiation signal emitted by the transmitter and/or a gain setting of the receiver;
receive the output signal from the receiver; and
compare a value of the output signal with one or more threshold values, the controller having:
a first sensor configuration in which the controller causes the transmitter to emit a first electromagnetic radiation signal having a first intensity and the receiver to have a first gain setting, the output signal provided to the controller by the receiver being a first output signal indicative of the amount of the electromagnetic radiation received at the receiver; and
a second sensor configuration in which the controller causes the transmitter to emit a second electromagnetic radiation signal having a second intensity and the receiver to have a second gain setting, the output signal provided to the controller by the receiver when in the second sensor configuration being a second output signal indicative of the amount of electromagnetic radiation received at the receiver,
wherein the first intensity is different from the second intensity, and/or the first gain setting is different from the second gain setting, and the controller compares the first output signal with a first threshold value, and determines that a humidification chamber in a respiratory gas humidifier is in either i) a first state, or ii) a one of two further states, and when it is determined that the humidification chamber is in ii) one of two further states, the controller compares the second output signal with a second threshold value to determine whether the humidification chamber is in a second state or a third state.
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