EMI & RFI Interference Testing

RF Surveys

There is often a requirement to measure existing electromagnetic energy levels at proposed sites which may be earmarked for installation of sensitive electronic measurement equipment. Modern, calibrated Spectrum Analysers, RF Antennas and Probes are used to measure background or ambient ELF and RF levels to determine if the site is suitable. Professional test reports are prepared using the data.

Pre and post surveys are performed at sites where electrical and electronic equipment is intended for installation, to assess the impact on the environment and any existing sensitive electronic equipment.

Electromagnetic Interference

Every interference problem has the following elements:

Source: The device or equipment which is causing the interference problem, usually a radio transmitter, high voltage/high current source, electrical substation or non-compliant electrical/electronic equipment

Path or Medium: How the energy is transferred. Either conductively by inductive or capacitive means through cables or  metallic surfaces, or radiated through the air

Victim: The device or equipment which is being interfered with, usually sensitive electronic equipment or radio receivers

EMC

Interference Problems occur due to a lack of Electromagnetic Compatibility. The Source may be high powered and/or non-compliant, or it may be compliant but located too close to a sensitive device (or vice versa). The Victim may not have adequate EMC immunity.

Often the simple solution is to increase the separation between Source and Victim.

Non-compliant equipment may have to be reported to the authorities (ACMA). Sensitive Victims may have to be hardened by re-design or retro-fitted with EMI counter-measures. In some cases EMI Shielding must be installed.

Investigations

We are often called out to investigate real world EMI interference problems.

Common Sources (offenders) are Electronic Equipment (such as LED Lights, UPS, Power Supplies, devices with brush electric motors, Variable Speed Drives, electronic equipment with high speed circuits and/or high frequency clocks), Intentional Transmitters (operating at illegal power levels), Booster Amplifiers, Cellular repeaters (which are illegal), High Voltage Equipment (mains power sub stations) and vehicles (trains and trams).

Common Victims are Medical Imaging machines (MRI, Ultra Sound), Digital TV Receivers, Remote Controlled Machines, Keyless Entry on vehicles and various  devices with sensitive electronic control circuits and radio receivers.

In many cases the problem is caused by non-compliant electrical and electronic devices (not ACMA RCM Compliant!), or incorrect installation/operation of compliant devices (not fitted with essential RF filters, EMI suppression ferrites or not earthed correctly). In some cases compliant devices have been illegally modified.

Interesting Interference Case Studies Blog coming soon!

Test Equipment

An array of modern EMI tools (Calibrated Spectrum Analysers, EMI Receivers, RF Antennas, Probes) is used to investigate the cause of the problem.

Counter Measures

Mitigation strategies and counter-measures are then recommended (such as reporting Source operators or suppliers of non-compliant equipment to relevant authorities where warranted, relocation and separation of equipment, EMI shielding, modification and suppression of Source, immunity hardening of victim by fitment of EMI counter-measures).

In simple cases it is possible to implement a solution on the day.

Reports

We can prepare professional reports if required.

Standards

The following EMI and EMC standards are commonly applied:

• AS 2344 Limits of electromagnetic interference from overhead a.c powerlines and high voltage equipment installations in the frequency range 0.15 MHz to 3000MHz
• AS 2834 Computer accommodation
• AS/NZS CISPR 32 Electromagnetic compatibility of multimedia equipment – Emission requirements
• AS/NZS CISPR 24 Information technology equipment – Immunity characteristics

These can be purchased from SAI Global

Fact: Most interference problems are simple to solve (if you know what to look for!)