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Figure 10
. Block Diagram of the Q-300
The effect of the "Noise Floor" on low level readings can cause inaccurate data. In a "Perfectly Quiet" room, the
electrical noise produced by the microphone is approximately
35 dB on A weighting or 45 dB on C weighting.
Measurements must always be at least 5 dB above the "Noise Floor". to be valid. Therefore, the lowest possible
measurements of the dosimeter are approximately:
40 dB on "A" Weighting (Lowest Valid Reading).
50 dB on "C" Weighting (Lowest Valid Reading).
6. TECHNICAL INFORMATION
6.1 Principles of Operation
The Q-300 dosimeter uses low power state-of-the-art circuitry. The dosimeter is very stable and reliable over a wide range of
environmental conditions.
The low power circuitry gives the dosimeter a long battery life. When the 9 volt battery is changed, all dosimeter information is
retained due to an internal lithium battery. The lithium battery lasts for many years before needing replacement. (See
SPECIFICATIONS)
A rubber Key Pad is used for all data entry and settings. Menus appear on the display and the keys are used to enter changes.
A block diagram of the Q-300 is shown in Figure 11.
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Figure 11
. Q-300 Microphone Frequency Response.
6.2 Microphone Characteristics
The Q-300 Noise Dosimeter uses an 8 mm omnidirectional ceramic microphone. It is buffered by a high impedance FET input
stage. (See Figure 12.)