EMC standards usually state that the Equipment Under Test (EUT) must be tested in its worst expected conditions for the tests. The problem is, how you can know what are the worst conditions? Furthermore, they ask for executing the tests in a way that the EUT behaves in the same way, or similarly, to how it will be used in the real world. Sometimes this is possible due to the characteristics of the EUT, but for others, it is not manageable because of the absence of auxiliary equipment or time.
What is an operation mode?
It is a specific behavior of the EUT during a time period. This behavior needs to be a realistic representation of the actual behavior during real use of the EUT. If you are not 100% sure about the definition of the operation modes of your EUT, try to have the client’s approval before starting the tests.
When and where do we define the operation modes?
Before starting the EMC tests, when writing the EMC test plan. They will be also reflected in the test report written by the certification laboratory.
What is the impact of the operation modes?
We execute EMC tests to simulate radiated and immunity phenomena in real life. Therefore, to get a real representation, we need to bring real behaviors to the laboratory. The main aspects of a project that are impacted by the EUT operation modes are:
- Software: the execution of different types of behavior implies the development of a specific Sofware for each of them. The EUT will move cyclically from one operation mode to the next one. Also, it is a good practice to execute a batch of tests after each immunity test, so in case of failure, you can exactly detect what and when happened.
- Test duration: some standards give freedom to define the scanning time, which usually has to be long enough to cover the execution of each operation mode. This makes that, the longer the operation modes are, the longer the tests will be. It is frequent to find a balance between a good enough real representation and the duration of the tests.
- Hardware: you may need some specific auxiliary equipment for specific operation modes. It can be as simple as a LED, or more complex such as power resistors or inductances with cooling systems.
Example: a home use drilling machine
This EUT has a motor, so a good representation of its behaviour could be:
- Power the EUT on
- Increase the speed to its maximum in one sense
- Stay at maximum speed for some seconds
- Decrease the speed to its minimum
- Increase the speed to its maximum in the opposite sense
- Stay at maximum speed for some seconds
- Decrease the speed to its minimum
- Power the EUT off.
Steps 1 and 8 are important because they serve to detect whether the connection or disconnection to power provokes any undesired effects due to overcurrents. Repeat cyclically all the steps or, at least, from 2 to 7 during the complete test execution.
Are you preparing an EMC test campaign? Do you have questions? Please, do not hesitate in contacting us.
