Spec Study: Dynamic Range
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One of the specifications that is often published for signal analyzers and analog measurement devices is dynamic range. Instrument vendors frequently discuss this spec when promoting their products. But what does dynamic range really mean? Understanding this specification and how it affects a measurement can you help you find the right device for your application.
What is Dynamic Range?
Dynamic range is a ratio of the maximum signal and minimum signal that can measured at a single time. Expressed in decibels, the calculation for dynamic range is:Dynamic Range (dB) = 20 x log (Maximum Voltage / Minimum Voltage).
Because dynamic range is a specification of how small you can measure a signal relative to the maximum input signal the device can measure, it is very closely tied to the input range of the measurement device. For example, the NI 4472 has an input range of ±10 V and a dynamic range greater than 110 dB, for a voltage ratio of 106. Thus, with a maximum signal of 10 V, the smallest signal that you can see on the NI 4472 is 10 µV. Thus, the input range and the specified dynamic range are important for determining the needs of your system.
The Effects of Dynamic Range
The effects of high dynamic range are most apparent when doing analysis in the frequency domain. For example, consider the application of testing an audio amplifier. One of the tests that may be performed is frequency response using a dual-tone signal. The signal may have one component at 10 kHz, a large amplitude sine tone, and another sine tone at 1 kHz with a much smaller amplitude. The 118 dB dynamic range of the NI 4461 means that the smaller signal will be detected easily and a more complete characterization of the amplifier’s performance can be done. In addition, the NI 4461 offers programmatic gain for applications such as low-level vibration analysis so that the input range of the measurement device can be adjusted to match the output of the accelerometer.
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10 Questions to Ask When Selecting Your Sound and Vibration Measurement System
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