Conducted immunity testing injects disturbance pulses into a product through its supply or signal lines, reproducing the transient conditions found in a vehicle electrical system. The product must keep functioning normally under such disturbance. Automotive work follows CISPR 25.
How the test works
Standard disturbance pulses are applied to the product's supply or signal lines through a coupling network or by direct injection. Typical automotive sources include load dump, jump starting, generator faults and ignition transients.
The product runs normally during the test with its function monitored, and any anomaly after a pulse is observed.
Common disturbance types
Transient pulses: reproduce the voltage spikes generated by load dump and switching events.
Pulse bursts: reproduce the high-frequency pulse train generated when an inductive load is disconnected.
Voltage change and recovery: reproduce battery voltage fluctuation (the drop when the engine starts).
BCI bulk current injection: injects common-mode current onto signal lines, reproducing the induced current when a harness is exposed to an external field.
Common failures and corrective action
The product restarts momentarily → insufficient protection at the power input; add TVS devices and input filtering.
Communication data errors or frame loss → add series resistors and common-mode chokes on signal lines, and make critical signals differential.
Abnormal ADC readings → add RC filtering on analogue channels and design sampling for interference synchronisation.
EEPROM data corruption → add checksums and retry to write operations, and store critical data redundantly.
Frequently asked questions
How does conducted immunity differ from ISO 11452-2?
ISO 11452-2 is mainly a radiated immunity method at vehicle or large-component level, whereas conducted immunity in CISPR 25 is more device-level. In practice, product validation follows the standard the customer specifies — OEM validation usually cites corporate standards, and only whole-vehicle EMC validation uses the ISO 11452 series.
Why is my product still complained about after passing radiated immunity?
Because the interference path is different. Radiated immunity injects through a spatial field, while conducted interference enters through cables. The countermeasures differ: shielded cable is effective against radiated coupling but has limited effect on conducted interference, which usually also needs filtering and transient suppression devices.
Service notes
Our laboratory holds both CMA and CNAS accreditation, covers about 10,000 m2 and runs more than 500 sets of equipment. All testing is carried out in our own laboratories — nothing is subcontracted. Plant visits and on-site witnessed testing are welcome.
Scheduling follows the actual project pipeline. You can state your preferred lead time when you submit samples; we will confirm a feasible plan against current capacity and keep you updated at each milestone. Once the report is issued we send the electronic copy; corrective-action advice can be arranged separately.
