Transient recorders explained: When they are necessary and what matters

What are transient events?

In order to understand what a transient recorder is and what it is used for, we first need to understand ‘transient events’.

Transient events are short-term, abrupt changes in electrical quantities (typically voltage, current or power) that lie outside normal operating behaviour. They often occur as a result of switching operations, faults, overvoltages or interference.

Typical characteristics of transient events:

•     Duration in the microsecond to millisecond range
•     Very fast rise times
•     Often non-periodic, difficult to predict
•     Can cause disturbances and even damage

Examples of transient events:

•     Voltage peaks when large consumers are switched on
•     Short-circuit events in the power grid
•     Interference pulses caused by EMC events

What is a transient recorder?

A transient recorder (also known as an event recorder) is a specialised measuring device for recording transient (i.e. very fast, short-term electrical) events with high temporal resolution. It detects sudden changes in current, voltage or power and stores them for later measurement data analysis.

What are the characteristic measurement properties of transient recorders?

• Very high sampling rate
• Long, continuous recording (with triggers if necessary)
• Multi-channel capability
• Galvanic isolation (important for high-voltage applications)
• High resolution and synchronised recording

Typical areas of application

• Energy technology (grid disturbances, switching operations, voltage edges)
• E-mobility / battery testing
• High-voltage test benches
• Railway technology
• Research & development (e.g. for transient phenomena)

What is the difference between a transient recorder and an oscilloscope?

A transient recorder and an oscilloscope are both used to capture electrical signals, but they are optimised for different applications. The transient recorder is specifically designed to record short-term, unpredictable events, such as those that occur during power grid disturbances or high-voltage events. It scores with a very high sampling rate (typically 1–10 MS/s per channel), a long recording time (several seconds to minutes), large memory depth (e.g. via SSD), and comprehensive trigger functions. It also offers galvanic isolation as standard, making it ideal for high-voltage and industrial applications. Data evaluation is also often automated and integrated via specialised software.

An oscilloscope, on the other hand, is particularly well suited for repetitive or continuous signals. Although modern devices are equipped with extremely high sampling rates (often >1 GS/s), the recording time is usually significantly shorter because the internal memory (RAM) quickly reaches its limits. The trigger functions are also powerful, but are designed more for real-time display on the screen. Galvanic isolation is usually not provided. Therefore, oscilloscopes are more intended for laboratory use, as they are less robust against electromagnetic interference.

Choosing the right transient recorder

The selection of the right measuring device for recording transient events depends heavily on the area of application, particularly on the type of signals, the measuring environment and the requirements for accuracy and safety.

• High sampling rates (e.g. 1-10 MS/s) are required to cope with transient events. In addition, a resolution of at least 16 bits is necessary for precise recording.
• The number of channels required should be determined for the respective measurement task. If mains or high-voltage measurements are to be carried out, the channels should be galvanically isolated.
• A flexible trigger is crucial for accurately recording rare events, e.g. with lead/lag time, threshold value or edge detection.
• In order to be prepared for very long-term recordings, the transient recorder should either have sufficient storage space or offer appropriate export functions (e.g. MATLAB).
• Interfaces for integration into existing (software) systems can also be helpful.
• Depending on the application environment, the measuring device should also be mobile. A certain degree of robustness may also be a prerequisite, e.g. for blasting tests.