Characteristics of Analog Optical Isolators
(a)
(b)
(c)
(d)
Figure 3. Typical LED AOI Distortion Characteristics
At high AC voltages, distortion to the waveform can be seen using an
oscilloscope. The waveform is still symmetrical but contains the
fundamental and the odd harmonics, the third harmonic being
predominant. If there is DC as well as AC voltage on the photocell,
both even and odd harmonics are generated.
The RMS value of voltage or current is not very sensitive to a large
third harmonic component, but the instantaneous value is. A 10%
harmonic will only change the RMS values by 0.5%. If the output is
used to control a thermal element, such as a thermal relay, circuit
operation is not affected. Further, when the AOI is used in ON-OFF
applications, waveform distortion is not a problem.
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PERKINELMER [ PERKINELMER OPTOELECTRONICS ]
