Electronics Guide

Motor Drive Systems

Variable frequency drives (VFDs) powering assembly line motors are among the most significant EMI sources in manufacturing facilities. These drives convert AC power to DC and then synthesize variable-frequency AC using pulse-width modulation (PWM), generating broadband emissions from the switching frequency (typically 2-20 kHz) through harmonics extending into the MHz range.

VFD emissions propagate both as conducted interference on power cables and as radiated emissions from motor cables acting as antennas. The long cable runs typical in production facilities can be particularly effective radiators at frequencies where cable length approaches a quarter wavelength. A 10-meter motor cable becomes an efficient antenna around 7.5 MHz and its harmonics.

Mitigation strategies for VFD emissions include:

• Input and output filters designed for the specific drive and installation
• Shielded motor cables with proper termination at both ends
• Segregation of motor cables from signal and data cables
• Ferrite chokes on motor cables for additional high-frequency attenuation
• Proper grounding of drive enclosures and cable shields

Pneumatic and Hydraulic Systems

Pneumatic actuators and hydraulic systems generate electromagnetic interference through their control valves and associated electronics. Solenoid valves produce transients when energized and de-energized, with the inductive kick during turn-off being particularly problematic. These transients can couple into nearby circuits through conducted and radiated paths.

The high-pressure releases from pneumatic systems can also generate electrostatic discharge (ESD) events as air rushes past plastic components and tubing. This triboelectric charging can produce discharge events that affect sensitive electronics in the vicinity.

Control measures include snubber circuits across solenoid coils, proper cable routing and shielding for valve control wiring, and grounding of pneumatic system components to prevent charge accumulation.

Lighting Systems

Industrial lighting contributes to the electromagnetic environment in several ways. Fluorescent lighting generates emissions at the electronic ballast switching frequency and its harmonics. High-intensity discharge (HID) lamps produce broadband noise during ignition and can generate ongoing interference from unstable arc behavior.

LED lighting systems, while generally producing less EMI than older technologies, still generate switching noise from their driver circuits. High-power LED systems may require filtering to prevent conducted emissions from propagating onto shared power distribution systems.

Lighting placement should consider both the need for adequate illumination at work stations and the potential for interference coupling to sensitive test and measurement equipment. Shielded luminaires and filtered power connections may be necessary in areas where sensitive operations occur.

Servo Drive Emissions

Robot servo drives use PWM techniques similar to VFDs but often operate at higher switching frequencies (8-20 kHz) to achieve the dynamic response needed for precise motion control. Each robot axis has its own servo drive, so a six-axis robot may have six independent sources of switching emissions.

The cables connecting servo drives to motors are significant emission sources because they carry high-frequency PWM currents and may be several meters long. Robot designs that route these cables through articulated arms create variable cable geometries that can affect emission characteristics as the robot moves through its work envelope.

Modern robot manufacturers typically provide EMC-compliant systems, but proper installation is critical. This includes maintaining recommended cable lengths, using specified cable types, ensuring proper shield connections, and following grounding instructions in the installation manual.

End Effector Considerations

Robot end effectors (grippers, tools, and sensors) add additional complexity to robot EMC. These devices require power and signal connections through the robot arm, creating potential coupling paths between the robot's servo system and end effector electronics.

End effectors with their own motors (such as electric grippers) add emission sources at the robot tool point. Sensors and vision systems on end effectors may be susceptible to interference from the robot's own systems or from nearby manufacturing equipment.

Best practices for end effector integration include using shielded cables for all connections, providing filtered power to sensitive electronics, locating sensitive signal processing electronics in shielded enclosures away from the tool point, and establishing clean ground references independent of the robot structure.

Robot Cell Layout

The layout of robot work cells affects both the robot's EMC performance and its impact on surrounding operations. Key considerations include:

Cable routing: Robot power and signal cables should be routed away from sensitive equipment and measurement systems. Physical separation reduces both conducted and radiated coupling.

Grounding: Robot bases should be bonded to the facility ground system with low-impedance connections. Multiple ground connections may be needed for large installations to minimize ground voltage differences.

Controller placement: Robot controllers contain both the power electronics (servo drives) and sensitive control electronics. They should be located where cooling is adequate and where their emissions will not affect nearby operations.

Safety systems: Emergency stop circuits and safety interlock systems must be immune to electromagnetic interference to ensure reliable operation. These systems typically use relay-based logic or safety-rated PLCs with enhanced immunity.

Test System Shielding

Production EMC test systems often operate in environments far more hostile than typical EMC laboratories. Ambient electromagnetic noise from manufacturing equipment can corrupt measurements and cause false failures if not properly controlled.

Shielded enclosures (screen rooms) provide isolation from ambient interference for sensitive measurements. Production test enclosures may be smaller than compliance test chambers but must still provide adequate shielding effectiveness at the frequencies of interest. Typical production shielded enclosures achieve 60-80 dB of shielding at frequencies from 100 kHz to several GHz.

The shield integrity must be maintained through proper treatment of penetrations for power, signals, and material handling. Filtered connectors, waveguide-beyond-cutoff penetrations for cables, and pneumatic feedthroughs with proper RF sealing prevent shield degradation.

Test Fixture Design

Test fixtures provide the mechanical and electrical interface between the ATE system and the device under test (DUT). Fixture EMC performance directly affects measurement accuracy and repeatability.

Key fixture design considerations include:

Ground reference: The fixture must establish a consistent ground reference for the DUT that accurately represents the product's final operating environment. This may require a ground plane or controlled impedance reference structure.

Cable management: Test cables within the fixture should be short, shielded, and routed to minimize coupling between high-level and sensitive signals. Cable dress should be controlled and repeatable.

Contact quality: Test contacts must provide reliable, low-impedance connections to ensure measurement accuracy. Contact wear and contamination can affect both contact resistance and RF performance over time.

Fixture shielding: Some fixtures incorporate local shielding to provide isolation between test sections or to reduce coupling from nearby interference sources.

Measurement Correlation

Production EMC tests must correlate with compliance test results to ensure that passing production tests indicate compliant products. Achieving and maintaining this correlation requires careful attention to several factors:

Test environment differences: Production tests occur in different facilities with different ambient conditions than compliance tests. The correlation program must account for these differences and establish appropriate test limits.

Fixture effects: Production test fixtures differ from compliance test setups and may affect measured values. Correlation studies should quantify these effects and incorporate appropriate correction factors.

Equipment differences: Production test equipment may differ from compliance test equipment in specifications and performance. Cross-calibration and correlation testing verify that results are comparable.

Ongoing correlation monitoring compares production test results with periodic compliance tests on sample units to detect drift in the correlation relationship.

Motor and Drive Emissions

Conveyor drives generate emissions similar to other motor drive systems in the facility. Long conveyor runs may require multiple drive motors, each contributing to the overall emission environment. The extended length of conveyor systems means that power cables may run substantial distances parallel to other facility wiring, increasing coupling opportunities.

Modern conveyor systems often use distributed drive architectures with multiple small motors rather than single large drives with mechanical power distribution. While this approach offers operational advantages, it multiplies the number of EMI sources that must be controlled.

Static Charge Generation

Conveyor belts, particularly those made from insulating materials, can generate significant static charges as products move along the line. The triboelectric effect creates charge separation as dissimilar materials contact and separate, and conveyor motion provides continuous charge generation.

Static charges on conveyor systems can discharge to grounded objects or approaching personnel, potentially damaging static-sensitive components or corrupting sensitive electronic measurements. Static mitigation measures include:

• Static-dissipative belt materials that allow charge to drain to ground
• Ionizing systems that neutralize surface charges
• Grounding of all conductive conveyor components
• Humidity control to increase surface conductivity
• Proper personnel grounding procedures

Sensor and Control Systems

Conveyors incorporate numerous sensors for position detection, product identification, and safety functions. These sensors must operate reliably in the electrically noisy conveyor environment.

Photoelectric sensors are susceptible to interference from nearby VFD emissions, which can cause false triggering or missed detections. Shielded cables, filtered sensor power, and proper cable routing reduce susceptibility. Some sensors offer enhanced immunity options or digital communication protocols that are more resistant to interference than analog signal transmission.

Bar code scanners and RFID readers on conveyor systems must contend with both ambient interference and the emissions from their own high-frequency scanning or interrogation signals. Proper positioning and orientation of readers, along with adequate shielding, ensures reliable identification without interfering with nearby operations.

Resistance Welding EMI

Resistance welding (spot welding, seam welding, projection welding) uses high currents at low voltages to generate heat at the joint interface. Welding currents may reach tens of thousands of amperes, and modern welding controllers use thyristor or IGBT switching to control current flow.

The switching of these high currents generates substantial EMI with spectral content from the power line frequency through several MHz. The current path through welding cables and the workpiece creates a large current loop that radiates efficiently at lower frequencies, while the fast switching transitions generate higher-frequency emissions.

Mitigation approaches include locating welding equipment away from sensitive operations, using twisted or coaxial welding cables to reduce loop area, installing line filters on welding power supplies, and providing local shielding around welding stations when necessary.

Arc Welding Considerations

Arc welding processes (MIG, TIG, stick welding) generate particularly intense broadband interference from the welding arc itself. The arc is an unstable plasma that creates continuous noise with spectral components extending from audio frequencies through hundreds of MHz.

Arc welding power sources add their own interference from power conversion and current regulation circuits. Modern inverter-based welders operate at higher frequencies than traditional transformer-based units, generating different emission spectra that may require different mitigation approaches.

The combination of arc noise and power source switching noise makes arc welding one of the most challenging EMI sources in manufacturing. Physical separation, shielding, and careful facility layout are often necessary to protect sensitive operations from arc welding interference.

Welding Area Isolation

Given the intensity of welding EMI, isolation of welding areas from sensitive manufacturing operations is often the most practical approach. This may involve:

Physical separation: Locating welding operations at the periphery of the facility or in separate buildings reduces interference coupling to sensitive areas.

Shielded enclosures: Welding cells can be enclosed in shielded structures that contain emissions. The shielding must accommodate the large openings needed for workpiece access and address the grounding challenges posed by high welding currents.

Power distribution isolation: Separate power feeds for welding equipment prevent conducted interference from propagating to other loads. Isolation transformers or active power conditioners may be needed for particularly sensitive equipment sharing the same facility.

Timing coordination: In some facilities, welding operations can be scheduled to avoid simultaneous operation with the most sensitive manufacturing or test operations.

Vision System EMC

Machine vision systems use cameras, lighting, and image processing to inspect products for defects and verify assembly. These systems are susceptible to interference that can corrupt image data or cause communication errors.

Camera interfaces using protocols such as GigE Vision, Camera Link, or USB3 Vision transmit high-speed digital data that requires careful cable selection and routing. Shielded cables with properly terminated shields reduce both susceptibility to external interference and emissions that might affect nearby equipment.

Vision system lighting, particularly strobe systems, can generate EMI from their high-current pulsing. LED strobe systems with their switching power supplies and rapid current transitions may require filtering and shielding to prevent interference with the camera electronics they illuminate.

X-Ray and CT Inspection

X-ray inspection systems present unique EMC considerations due to their high-voltage generation and sensitive detector electronics. The X-ray tube high-voltage supply generates EMI from its switching power converter and from corona discharge in the high-voltage circuits.

X-ray detectors, whether image intensifiers, flat panel detectors, or CT detector arrays, use sensitive analog electronics to capture X-ray images. These must be protected from interference that could degrade image quality or cause artifacts.

X-ray systems typically operate within shielded enclosures for radiation safety, and these same enclosures provide EMI shielding. However, penetrations for material handling and control connections must maintain both radiation and EMI integrity.

Electrical Test Systems

In-circuit test (ICT), functional test, and boundary scan systems verify the electrical performance of manufactured assemblies. These systems make precise measurements that can be affected by ambient EMI and by interference generated by the test system itself.

Test system designers must ensure that measurement circuits are adequately shielded and filtered, that test signals do not interfere with measurement channels, and that the overall system provides accurate results in the production environment. Guard traces, driven shields, and careful signal routing reduce measurement errors from interference.

High-frequency measurements are particularly challenging in production environments. Network analyzer and spectrum analyzer measurements may require local shielding or scheduling during quiet periods to achieve adequate accuracy.

Automated Guided Vehicles

Automated guided vehicles (AGVs) and autonomous mobile robots (AMRs) use wireless communication, navigation systems, and motor drives that create EMC interactions throughout the facility.

AGV wireless systems must coexist with other facility wireless networks and must maintain reliable communication despite industrial EMI. The mobile nature of AGVs means they encounter varying electromagnetic environments as they move through the facility.

AGV navigation systems using magnetic guides, laser scanning, or camera-based localization each have specific EMC requirements. Magnetic guidance systems must contend with stray magnetic fields from motors and transformers, while optical systems must handle the varied lighting conditions of industrial environments.

AGV motor drives generate the same types of emissions as stationary drives, but their mobility spreads these emissions throughout the facility. Proper filtering and shielding of AGV drive systems prevents interference with sensitive operations along AGV routes.

ESD Control in Material Handling

Material handling equipment can generate, transfer, or dissipate static charges that affect product ESD protection. Maintaining ESD control through the material handling process is essential for products containing static-sensitive components.

Key control points include:

• Conductive or static-dissipative totes and carriers that prevent charge accumulation
• Grounding of handling equipment including conveyors, racks, and carts
• Personnel grounding through flooring, footwear, and wrist straps
• Ionization systems at locations where insulating materials must be handled
• Humidity control to maintain surface conductivity

Lift and Positioning Systems

Overhead cranes, hoists, and positioning systems support assembly operations with heavy or awkward components. These systems typically use large motors or servo systems that generate substantial EMI.

The elevated position of overhead systems and their long cable runs can make them effective radiators of interference. Shielding of motor cables and proper grounding of crane structures reduces emissions that might affect floor-level operations.

Some positioning systems use variable frequency drives with regenerative capabilities that return energy to the power system during braking. The power flow reversals during regeneration can create power quality disturbances that affect other equipment on the same power distribution system.

HVAC System EMC

Heating, ventilation, and air conditioning (HVAC) systems are significant EMI sources in manufacturing facilities. Large blower motors, compressors, and their variable speed drives generate emissions similar to other motor systems but often at higher power levels.

HVAC control systems increasingly use variable speed drives for energy efficiency, replacing the simpler on-off control of older systems. While beneficial for energy consumption, these drives add EMI sources distributed throughout the facility.

HVAC ductwork can act as waveguides that propagate EMI throughout the facility or as antennas that radiate interference. Proper bonding of ductwork to ground reduces these effects, while filters at duct penetrations into shielded rooms prevent EMI leakage.

Humidity Control for ESD

Relative humidity significantly affects electrostatic discharge behavior. Low humidity allows higher charge accumulation and more energetic discharge events, while higher humidity provides surface conductivity that helps drain charges before they reach damaging levels.

Many electronics manufacturing facilities maintain humidity levels between 40% and 60% RH to balance ESD protection with comfort and equipment requirements. Humidity control systems must operate reliably to maintain these levels consistently.

Local humidification at ESD-sensitive work stations can supplement facility-wide humidity control in dry climates or seasons. However, humidification equipment itself may generate EMI from pumps, fans, and control systems.

Cleanroom EMC Considerations

Cleanrooms for electronics manufacturing add EMC considerations beyond those of general manufacturing areas. The HEPA filtration systems require substantial blower power, and the laminar flow requirements may dictate fan locations close to sensitive operations.

Cleanroom construction materials affect both contamination control and electromagnetic shielding. Some cleanroom designs incorporate conductive materials for ESD control that also provide EMI shielding, while others use insulating materials that require additional EMI protection measures.

The positive pressure maintained in cleanrooms requires careful treatment of penetrations for utilities, process gases, and material handling. These penetrations must maintain both cleanroom integrity and EMI shielding when operating in shielded areas.

Measurement Station Design

Quality measurement stations must be designed to provide accurate, repeatable measurements despite the electromagnetic noise of the surrounding production environment. Key design considerations include:

Location selection: Position measurement stations away from major EMI sources such as welders, large motors, and power electronics. Identify quiet locations within the facility through electromagnetic surveys before station installation.

Local shielding: When measurement stations cannot be located in quiet areas, local shielding may be needed. This can range from simple shielded enclosures around sensitive instruments to complete shielded rooms for critical measurements.

Power quality: Provide clean power to measurement equipment through isolation transformers, power conditioners, or uninterruptible power supplies. Separate power feeds from production equipment reduces conducted interference.

Grounding: Establish a clean ground reference for measurement equipment that is isolated from production equipment grounds. This may require dedicated ground conductors and careful attention to avoiding ground loops.

Test Equipment Selection

The selection of test equipment for quality stations should consider EMC performance alongside measurement capability. Key factors include:

Immunity specifications: Test equipment immunity to EMI, often specified in accordance with standards such as IEC 61326, indicates how well the equipment will perform in industrial environments. Select equipment with immunity levels appropriate for the installation environment.

Filtering options: Some test equipment offers optional input filters that improve immunity at the expense of measurement bandwidth. These options may be valuable for measurements that do not require the full instrument bandwidth.

Shielding quality: Well-shielded test equipment resists interference better than poorly shielded units. Metal enclosures with proper gasketing and filtered connectors indicate attention to EMC in the equipment design.

Communication interfaces: Digital communication interfaces for data collection should be selected for noise immunity. Fiber optic interfaces provide complete galvanic isolation and immunity to EMI, while properly implemented Ethernet can provide adequate performance in most industrial environments.

Operator Interface Considerations

Quality station operator interfaces must function reliably in the production environment while providing clear information for quality decisions. Display technologies vary in their EMC characteristics:

LCD displays: Modern LCD displays are generally resistant to EMI but may show interference artifacts under extreme conditions. Touch screen interfaces add susceptibility considerations for the touch sensing system.

Indicator lights: Simple LED indicators are highly resistant to EMI and provide reliable status indication in noisy environments.

Audio alerts: Audible alarms must be distinguishable from production noise and immune to false triggering from EMI. Audio systems with proper filtering and shielding provide reliable alerting.

Human-machine interfaces should be located and oriented to minimize interference from the operator's body and from nearby production equipment while providing ergonomic access for the operator.

Zoning by EMC Characteristics

Grouping production operations by their EMC characteristics simplifies interference management. A typical zoning approach might include:

Heavy industrial zone: High-power equipment, welding, and processes with intense EMI are grouped together at the facility periphery or in separate buildings. This zone accepts higher interference levels and focuses on preventing emissions from reaching other zones.

General manufacturing zone: Typical production equipment operates in this zone with standard industrial EMC controls. Equipment in this zone must be compatible with normal industrial EMI levels.

Sensitive operations zone: Precision measurement, EMC testing, and assembly of highly sensitive products occur in this zone. Additional shielding, filtering, and power conditioning protect these operations from interference generated elsewhere.

Buffer zones between incompatible operations provide physical separation that reduces coupling. These zones may contain support functions such as storage, offices, or break areas that have minimal EMC requirements.

Power Distribution Architecture

The facility power distribution system can propagate conducted EMI throughout the building or can provide isolation between incompatible loads. Key design decisions include:

Separate feeders: Providing separate power feeders for high-EMI loads and sensitive loads prevents conducted interference propagation. The additional infrastructure cost is often justified by improved EMC performance.

Transformer isolation: Isolation transformers block common-mode noise and provide some differential-mode attenuation. Placing transformers between EMI sources and sensitive loads reduces conducted coupling.

Filtering at distribution panels: Power line filters at distribution panels prevent interference from propagating between circuits. This approach addresses interference at a central point rather than requiring filtering at each piece of equipment.

Clean ground systems: Establishing separate ground systems for sensitive equipment prevents ground-coupled interference from production equipment. The separate systems must be bonded at a single point to prevent hazardous voltage differences.

Cable Routing Infrastructure

Cable routing affects both conducted and radiated coupling between systems. Well-designed cable infrastructure separates incompatible cable types and provides appropriate shielding:

Segregated cable trays: Separate cable trays for power cables, control cables, and signal cables prevent coupling between cable types. Adequate separation between trays or solid barriers provides additional isolation.

Cable tray materials: Metal cable trays provide some shielding when properly bonded and grounded. Tray covers increase shielding effectiveness for critical cable runs.

Routing discipline: Establishing and enforcing cable routing standards prevents ad-hoc installations that create interference problems. Documentation of cable routes supports troubleshooting and future modifications.

Penetration management: Cable penetrations through walls, floors, and shielded enclosures require proper treatment to maintain isolation. Filtered connectors, conduit, or waveguide penetrations address different requirements.