In the previous article, we learned about EMI/EMC pre-compliance testing. EMS/EMC pre-compliance immunity testing is required prior to compliance testing.
EMS/EMC pre-compliance immunity testing will give you the confidence to pass compliance testing. Pre-compliance immunity testing simulates all tests performed in the compliance testing laboratory, but it is unnecessary to apply all tests to the equipment under test (EUT). Testing depends on the application and country's EMC regulatory standards. Since compliance testing is expensive, all troubleshooting must be resolved in pre-compliance testing.
Fig.1 Pre-compliance test block diagram
This article is about different EMS/EMC pre-compliance immunity tests and how these tests can be performed in small laboratories. Many labs offer immunity tests, but this article attempts to make a simple and straightforward setup for different types of tests.
Enter pre-compliance immunity testing
As discussed in a previous article, EMS/EMC immunity testing is performed to ensure that the device can survive the different interferences generated by other devices. The most common EMS/EMC immunity tests are given below in the block diagram.
Fig. 2 Immunity test block diagram
Continuous Immunity Test
Irradiated Pre-Compliance Immunity Test
Radiated emission are RF electromagnetic signals produced by devices in the environment. Mobile devices, TVs and other devices generate electromagnetic interference through the air, which can be a serious problem for other devices. Radiated pre-compliance immunity testing simulates this condition to test the device in a simulated environment before moving to compliance testing.
To perform this test, you need an RF signal generator that generates an RF signal and an amplifier to amplify the signal. The output of the amplifier is connected to the antenna to transmit the signals through the EUT.
RF signal generator
To perform this immunity test, we need to generate an RF signal transmitted at the EUT (equipment under test). But if the frequency range does not meet the device's requirements, the large and expensive RF signal generator will work very well to achieve the device's range.
Fig. 3 RF signal generator
RF Signal Amplifier
RF amplifier is used to get more gain in the signal. The amplifier depends on the requirements and need of the output device. The amplifier shown in the image has a gain of +20db.
Fig. 4 RF signal amplifier
EMC probes
EMC probes are used to detect electromagnetic interference in circuits, but can be used as an antenna to transfer RF signals to the device. Connect the RF signal generator to these probes through an RF amplifier and test the immunity and signal variation by passing the probe through the circuit. This process is very accessible and easy to set up.
Fig.5 EMC immunity test by EMC probe
TEM cell
TEM cell stands for “transverse electromagnetic cell” and is the second most affordable equipment for radiated immunity testing, but a little expensive than EMC probes. The frequency range depends on the geometry of the cell – the larger cell has a lower frequency range, but the smaller cell has a higher frequency range. The diagram below shows the signal generator connected to an amplifier that will be connected to a TEM cell that has a resistance of 50 Ohm at the other end.
Fig. 6 TEM cell for immunity testing
Pre-compliance immunity test performed
A plugged-in immunity test is performed on the AC or DC power cords. In this test, an RF signal is injected into the cables to test the device's immunity. Similar to the radiated immunity test, an RF signal generator is used to generate signals. The generated signal is amplified by an RF power amplifier. The amplified signal will be injected into the EUT cables by the transducer (CDN, BCI probe or EM clamp).
Fig. 7 Pre-compliance immunity test performed
Magnetic Precompliance Immunity Test
In magnetic precompliance immunity testing, equipment is placed between magnetic fields to check immunity. The test setup consists of a variac, current transformer and loop antenna. The setup is the same for transient and continuous immunity tests.
Fig. 8 Pre-compliance magnetic immunity test
Transient Immunity Test
ESD Pre-Compliance Immunity Testing
ESD stands for electrostatic discharge – a sudden flow of electricity between two electrically charged objects, commonly discharged through the human body. This test can be performed by an ESD simulator device.
There must be a ground reference plane on the laboratory floor in the test setup. The grounding system must be connected to the casing of the Equipment under test. There are two coupling planes used as shown in the image. One is horizontal and the other is vertical. A sheet of insulation is placed between the horizontal planes.
Fig. 9 ESD simulation setup
To simulate ESD, we can use a low-cost camping lighter to perform the ESD immunity test. A camping lighter can produce hundreds or thousands of volts, which is enough to generate sparks between conductive surfaces.
Fig. 10 ESD simulation device
EFT Pre-Compliance Immunity Test
EFT stands for electrical fast transient, caused by the switching of inductive loads such as motors, switches and relays. A burst generator is used to simulate inductive load switching. An EFT burst generator generates bursts of specific time, frequency, and amplitude to perform this test. This generated pulse burst is injected into the device via a capacitive clamp. You can buy or make the capacitive clamp.
Fig. 11 EFT Test
Precompliance Outbreak Immunity Testing
A surge test is used to simulate the effect of lightning on the AC power supply and is performed on longer cables. This test includes voltage around kV and current around hundreds of Amps. For pre-compliance surge immunity testing, you need a surge generator. There is some equipment available on the market that can generate EFT, surges and electromagnetic waves. The generated surge is injected through the coupling of the decoupling network device.
Fig. 12 Surge Pre-Compliance Test Setup
The frequency spectrum of surge testing is lower than EFT and ESD testing, so the test setup does not need a reference plane. But it requires a terrestrial.
Voltage Drop Pre-Compliance Immunity Test
In voltage drop pre-compliance testing, we simulate voltage drops (instantaneous voltage drop) over a specific time. The instantaneous voltage drop for a specific percentage can be imitated by automatically controlled variac and the time of drops is controlled by the UCS500N5 immunity test generator.
Fig. 13 Voltage drop pre-compliance test
