Pulsed magnetic field testing is a critical electromagnetic compatibility (EMC) immunity test that verifies whether robotic systems can withstand intense, short-duration magnetic field transients caused by lightning strikes, power system faults, and high-current switching events. Performed in accordance with IEC 61000-4-9, this experiment helps robot manufacturers prove operational reliability in harsh industrial electromagnetic environments. This article explains the technical principles, applicable samples, test items, test methods, and practical applications of pulsed magnetic field experiments for robots.
Technical Overview
A pulsed magnetic field experiment is a standardized immunity test that evaluates the ability of a robot and its electronic subsystems to continue operating correctly when exposed to transient magnetic fields of very high peak intensity and short duration. The governing international standard is IEC 61000-4-9, which is mirrored in China by GB/T 17626.9. These transient magnetic fields typically originate from lightning strikes on buildings and external circuits, initial phase-to-ground faults in medium- and high-voltage substations, and abrupt switching events in high-current industrial equipment such as capacitor banks, welding machines, and induction heating installations.
The test waveform specified by IEC 61000-4-9 corresponds to a magnetic field impulse with a rise time of approximately 6.4 microseconds and a duration of approximately 16 microseconds, generated by injecting an 8/20 microsecond impulse current into an induction coil. The standard defines discrete test severities expressed as peak magnetic field strength: Level 1 at 100 A/m, Level 2 at 300 A/m, and Level 3 at 1000 A/m, with additional special levels defined by product committees or user specifications. For equipment intended for industrial environments, the generic immunity standard IEC 61000-6-2 commonly requires the 1000 A/m severity level.
For robots, the significance of this test has grown alongside the deployment of robotic systems in power plants, substations, steel mills, welding lines, and rail transit depots, where powerful transient magnetic fields can induce spurious voltages in encoders, sensor cables, and control circuits. A robot that has not been validated for pulsed magnetic field immunity may experience sensor errors, servo faults, communication interruptions, unintended motion, or safety function degradation when such transients occur.
Testing Samples
Industrial Robot Controllers and Control Cabinets
The robot controller is the core sample type for pulsed magnetic field experiments. It contains motion control processors, safety logic, drive interfaces, and communication modules whose susceptibility to transient magnetic fields directly determines overall robot availability. Controllers are tested in their final enclosure with representative cabling connected.
Servo Drives, Encoders, and Motor Power Modules
Servo drives and feedback devices such as absolute encoders and resolvers rely on low-level analog and digital signals that are vulnerable to magnetically induced interference. Testing these components verifies position tracking accuracy and torque stability during and after magnetic transients.
Automated Guided Vehicles and Autonomous Mobile Robots
AGVs and AMRs operate on factory floors surrounded by heavy electrical infrastructure. Their onboard controllers, lithium battery management systems, navigation sensors, and wireless communication units are evaluated to confirm reliable path following and safe stop behavior under pulsed field exposure.
Robot Safety and Peripheral Components
Safety-related devices, including emergency stop circuits, safety relays, light curtains, collaborative robot joint torque sensors, and force-torque sensors mounted on end-effectors, are tested to demonstrate that protective functions remain intact during transient events, consistent with the safety requirements framework of ISO 10218 for industrial robots.
Special-Purpose Robots in Electrical Environments
Power line inspection robots, substation patrol robots, rail catenary maintenance robots, and nuclear facility handling robots are exposed to some of the strongest transient magnetic fields of any robotic applications, making them priority samples for high-severity testing.
Testing Items
A complete pulsed magnetic field experiment for robots typically covers the following items, tailored to the applicable product or generic standard:
- Pulsed magnetic field immunity at 100 A/m, 300 A/m, and 1000 A/m severity levels, or customer-specified special levels
- Immunity testing with both positive and negative pulse polarities, with a minimum of five pulses of each polarity at every specified level
- Exposure of the equipment under test along three orthogonal field orientations by rotating the induction coil or repositioning it around the sample
- Verification of the impulse waveform parameters, including rise time, duration, and peak field strength, before testing
- Field uniformity confirmation within the coil reference volume in accordance with IEC 61000-4-9 calibration requirements
- Functional monitoring of the robot controller, drive system, sensors, and safety functions during exposure to assign a performance criterion
- Testing under rated supply voltage conditions, and where relevant, under specified voltage variations defined by the product standard
Testing Methods
Test Equipment and Configuration
The test system consists of an impulse current generator, a standard square induction coil of one meter by one meter, and monitoring instrumentation. The equipment under test is placed at the center of the coil on an insulating support above a ground reference plane, operated in a mode that represents realistic use. For large control cabinets that exceed the coil dimensions, the immersion technique is applied: the coil is moved sequentially around the sample with overlapping positions so that the entire volume is exposed.
Calibration and Verification
Before testing, the magnetic field waveform is calibrated using the induction coil and a calibrated field measuring sensor or search coil. The laboratory verifies the rise time, duration, and peak field strength, and confirms that field uniformity within the reference volume meets the tolerance defined in IEC 61000-4-9. Climatic conditions are maintained within the standard ranges, typically 15 to 35 degrees Celsius and 25 to 75 percent relative humidity.
Test Procedure
The induction coil is first oriented to produce a field along one axis of the sample. Pulses of the specified severity are applied in positive polarity, then repeated in negative polarity, while the robot or subsystem performs its monitored function. The coil is then rotated 90 degrees to expose the second horizontal axis, and repositioned or reoriented to expose the vertical axis, so that the sample is challenged from all three orthogonal directions. Test engineers record any deviation from normal behavior, including data errors, resets, and recovery time.
Evaluation of Results
Results are assessed against performance criteria defined by the applicable product family or generic standard. Performance criterion A requires normal operation within specification during and after the test, which is the usual requirement for magnetic field immunity under IEC 61000-6-2. Criterion B permits temporary degradation or loss of function that is self-recoverable. A sample passes only if the assigned criterion is met for all axes, polarities, and severity levels.
Applications
Pulsed magnetic field experiments support robot development and market access across many scenarios:
- Compliance demonstration for industrial robots and integrated robotic cells against industrial immunity requirements referenced by IEC 60204-1 for electrical equipment of machines
- Qualification of substation patrol robots, power plant material handling robots, and grid inspection robots operating close to high-voltage switchgear and busbars
- Validation of welding robots and material processing robots installed near resistance welding and induction heating equipment that generate strong transient fields
- Verification of AGV and AMR fleets deployed in steel mills, foundries, and heavy manufacturing halls
- Design feedback during research and development, identifying sensitive circuits, improving enclosure shielding, and optimizing cable routing and grounding
- Technical documentation for CE marking conformity files and for customer or regulatory acceptance by accredited third-party laboratories
FAQ
What is the difference between pulsed magnetic field and power frequency magnetic field testing?
Power frequency magnetic field testing per IEC 61000-4-8 applies a continuous 50 or 60 Hz field, simulating steady currents in power lines and transformers. Pulsed magnetic field testing per IEC 61000-4-9 applies short, high-peak transients that simulate lightning-induced and fault-induced events. Robots installed near electrical infrastructure often require both tests.
Which test level applies to industrial robots?
For equipment intended for industrial environments, IEC 61000-6-2 commonly specifies a pulsed magnetic field severity of 1000 A/m. Lower levels such as 100 A/m or 300 A/m may apply to protected environments, while special-purpose robots in substations may be evaluated at higher customer-defined levels.
How many pulses are applied during the test?
IEC 61000-4-9 requires a minimum of five pulses of each polarity for each coil orientation and severity level. Accredited laboratories may increase the pulse count based on product standards or client specifications to improve statistical confidence.
What happens if a robot fails the test?
Failures typically appear as encoder glitches, servo alarms, communication dropouts, or controller resets. Corrective actions include improving enclosure shielding and bonding, rerouting or twisting sensitive cables, adding filtering and surge suppression on signal lines, and reinforcing grounding of the control cabinet, followed by retest verification.
Is pulsed magnetic field testing mandatory for all robots?
The requirement depends on the applicable product standard, the intended environment, and contractual or regulatory demands. Robots deployed in electrically severe locations such as power plants, substations, and heavy industrial plants almost always require this test, while robots for residential or light commercial use may face reduced or different requirements.