Background
IEC 61000-4-11 is an EMC test standard titled ‘Testing and measuring techniques – Voltage dips, short interruptions and voltage variations immunity tests’. It defines the setup, equipment requirements, and other conditions for testing systems to changes in the AC mains voltage. It is frequently used to show compliance.
Description of test standard
The standard describes three different tests:
1. Voltage dips are defined as sudden reduction in voltage to lower voltages for a short period of time, followed by recovery to the original voltage.
2. Short interruptions are defined as a disappearance of AC voltage for a short period of time, typically not exceeding 1 minute, followed by recovery to the original voltage. Short interruptions can be considered as voltage dips to zero volts.
3. Voltage variations are gradual changes of the supply voltage to a higher or lower value than the rated voltage. The duration can be short or long.
The standard also describes how the test results should be listed. Results of immunity tests are classified into four categories:
• Performance Criteria A – ‘Performance within specification limits’
• Performance Criteria B – ‘Temporary degradation which is self-recoverable’
• Performance Criteria C – ‘Temporary degradation which requires operator intervention’
• Performance Criteria D – ‘Loss of function which is not recoverable
Describing test results by performance criteria gives a clear idea of how the equipment responded. Criteria A (‘Performance within specification limits’) is clearer that ‘Display flashed’.
In addition, while no manufacturer would manufacture products only meeting Criteria D (‘Loss of function’), this emphasizes that the test standard is focused on recording the results of the test, regardless of the result.
It’s important to note that the test standard does not tell you the minimum performance criteria required for the product, what test level to use, or the duration of the test voltage. In fact, it allows you to document tests performed at levels & time durations not listed. This allows the standard to be used for future conditions not envisioned when it was written.
So if this test standard doesn’t tell you what test levels to use, or the minimum performance criteria for compliance, where is that information listed? The system EMC standard
Conclusion
IEC 61000-4-11 describes many details of testing equipment response to AC voltage changes. However, more information from other standards is needed, along with the system manufacturer’s intimate knowledge of his requirements. Correct testing can result in a system that is smaller, more cost effective, and is available to the marketplace in a timely fashion.