| 摘要 |
A housing or barrel has a source of light at one end and a pair of photosensors e.g. photodiodes at the other end, one of which is positioned to receive rays directly from the light source and the other of which is oriented in a different direction. Light is received only after the rays from the source have struck the specimen and are scattered back onto the second sensor. The source is mounted at the top of a barrel with the photodiodes positioned at the lower end of the barrel. The photodiodes are provided with a central opening through which a portion of the bundle of rays passes onto the specimen and is thus reflected onto the photosensitive surface of the second diode. Circuitry is provided for amplifying and comparing the signals received from the two photosensitive surfaces. The comparing circuit may comprise a divider for establishing a ratio between the signals from the phototiodes.
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