An oscilloscope can be very useful in determining rise times, ringing, and may even have frequency-domain capabilities. However, a real time spectrum analyzer is the preferred instrument for EMI troubleshooting or pre-compliance measurements. Depending on the standard, CISPR detectors may be required for pre-compliance scanning. These detectors can detect peak, avg and quasi-peak (QP). CISPR detectors may be required for pre-compliance scanning. Make sure that your spectrum analyzer can support them when needed. Refer to your standard(s), if applicable, to find out exactly what you need.
The standards and regions that you are testing for will determine the frequency range. The frequency clock that is included in your design will determine the frequency range. The maximum frequency measurement range refers to the frequency at which the device generates or uses the most emi testing lab frequency, or the frequency on which it operates or plays music. The FCC has provided a table 2 that shows the definition of unintentional radiators.
EMC testing is required to obtain a certificate of Electromagnetic Emissions and Immunity before the product can be launched on the market. But, EMC testing is expensive. The product must be tested in an EMC pre-compliance lab before it can undergo the actual EMC testing. Pre-compliance testing mimics all tests done at EMI/EMC labs to make sure the device passes the EMI/EMC compliance check. Pre-compliance testing is less expensive than the actual cost for EMI/EMC compliance labs, and it will produce approximately the same result.
The EMI/EMC, as mentioned in previous articles is an emission test that measures electromagnetic interference produced by the device. The limits for EMI or Electromagnetic interference tests Limits are determined by country regulations. It also depends on the device or product being used. Medical equipment must be precise in all conditions, so EMI/EMC testing is necessary. Medical devices that emit any kind of emission can cause false readings in other devices.
Block diagram is the most commonly used test that can be performed on nearly all devices. Failures in EMI testing could be due to PCB design, shielding and components, or antennas. All of these can cause radiated or conducted emissions. This is why the majority of failures in the EMI testing are in Radiated and Conducted emissions. Here are some methods to measure conducted and radiated emissions at the DIY laboratory.
There are two methods that can measure radiation emission: the far-field and near-field methods. Let’s first understand the differences between far-field and near-field measurements to determine how we can measure radiation emission in these fields. A magnetic field is created when oscillating electricity passes through conductors. As shown below, an electrified field is also created by the induced magnetic field. The magnetic field is represented by the H field and the electric field by the E field.
Both E and H fields will be produced by the equipment or device under test. The near-field electric field will have a high impedance, while the near-field magnetic field will have a lower impedance. The magnetic field and electric field combine at the same resistance at a distance. This is called a far-field. The frequency of waves determines the distance between the E and H fields.