Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Understanding Conducted Transient Emissions Testing with SAE J1113-42
1. Overview and Rationale
SAE J1113-42, officially titled “Electromagnetic Compatibility—Component Test Procedure—Part 42—Conducted Transient Emissions,” was a standard defining a laboratory bench test procedure for measuring conducted transient emissions from automotive electronic devices. While the standard was cancelled in December 2010 in favor of ISO 7637-2, its technical specifications and test philosophy remain influential. This article provides a practical overview of the measurement setup, key apparatus requirements, and considerations for engineers implementing transient emissions testing, whether referencing the legacy standard or transitioning to the international replacement.
The measurement philosophy centers on evaluating disturbances generated by inductive loads such as motors, solenoids, and relays. These transients propagate through the vehicle’s electrical system and can interfere with sensitive electronics. The test method provides a standardized bench approach to characterize these emissions.
⚠️ Important Note: SAE J1113-42 was cancelled in December 2010 and superseded by ISO 7637-2. It is recommended to use the international standard for new compliance testing. However, understanding this procedure is valuable when interpreting legacy test data or when specified in older component requirements.
2. Critical Test Apparatus Specifications
Repeatable measurement of conducted transients depends on strict control of test equipment. The standard specifies an artificial network (AN), oscilloscope, voltage probes, power supply, shunt resistor, and switching device. Each element must meet minimum performance requirements.
2.1 Artificial Network (AN)
The 5 µH AN is central to the setup. It simulates the impedance of the vehicle wiring harness. It must handle the DUT load current (typically 50 A) and be terminated with 50 Ω on its EMI port to avoid impedance mismatch.
2.2 Oscilloscope and Probes
The data acquisition system must capture fast transients with high fidelity. The table below summarizes the requirements.
| Parameter | Requirement |
|---|---|
| Oscilloscope Bandwidth | DC to 400 MHz minimum |
| Sampling Rate (digitizing) | 0.5 ns/sample or less |
| Probe Selection (transients >200 V) | 100x probe, breakdown ≥1.5 kV |
| Probe Selection (transients ≤200 V) | 10x probe, breakdown ≥250 V |
| Probe Ground Lead Length | ≤130 mm |
| Probe Bandwidth | DC to 400 MHz |
Using a 100x probe for low-amplitude events reduces signal-to-noise ratio, while a 10x probe may break down for high-voltage spikes. The ground lead must be as short as possible to minimize stray inductance.
2.3 Power Supply and Shunt Resistor
The DUT must be powered by a fully charged 12 V battery maintained at 13.0 V ± 0.5 V. A charger may be used to maintain voltage but must be disconnected during measurement to avoid noise. The shunt resistor Rs (default 40 Ω) simulates parallel vehicle loads; omitting Rs gives a worst-case condition.
🛠️ Engineering Design Insight: The placement of the switch S (between battery and AN vs. between DUT and AN) significantly affects transient characteristics. For slow transients (ms), Figure 3A is used; for fast transients (ns to µs), Figure 3B is used. Always document the configuration in the test plan to ensure reproducibility.
3. Best Practices and Common Pitfalls
Understanding common mistakes helps ensure accurate and repeatable results.
- Inadequate oscilloscope bandwidth: Using an oscilloscope with less than 400 MHz bandwidth can miss fast transient edges.
- Incorrect probe selection: Using a 10x probe for >200 V may cause breakdown; using a 100x probe for <200 V reduces resolution.
- Shunt resistor omitted without documentation: If Rs is omitted, treat it as a worst-case condition and document.
- Switch location unspecified: Always specify Figure 3A or 3B, or test both if unspecified.
- Relay contact degradation: Replace switching relay if contacts degrade to avoid distorted transients.
Frequently Asked Questions
1. Why was SAE J1113-42 cancelled?
The standard was cancelled because its content was superseded by the international standard ISO 7637-2, which provides a globally harmonized test method for conducted transient immunity and emissions.
2. What are the key differences between SAE J1113-42 and ISO 7637-2?
While both cover conducted transient emissions, ISO 7637-2 includes immunity testing and more comprehensive test pulse definitions. The test setup and apparatus are similar, but ISO 7637-2 is now the reference for most automotive OEMs.
3. How do I choose the shunt resistor Rs value?
If the vehicle manufacturer does not specify, use the default 40 Ω. Rs simulates the parallel resistance from other loads on the same circuit. Omitting Rs creates a worst-case condition.
4. Is the 5 µH artificial network still relevant?
Yes, the 5 µH AN is also specified in ISO 7637-2 for conducted transient testing, so the same network can be used for both standards.
🛠️ For thorough validation, always run both switch configurations (Figure 3A and 3B) unless the test plan narrowly defines a single configuration. This ensures all possible transient behaviors are captured.
