Immunity Testing Capabilities
Susceptibility or Immunity is the ability of the receptor or victim equipment to operate correctly in the presence of electromagnetic disturbances. Susceptibility and immunity are opposites – an equipment which has high susceptibility has low immunity, and vice versa.
Testing a device to measure its susceptibility to a disturbance requires a limit based on how a product is expected to behave during and after an event. These events, or phenomena, are either continuous or transient disturbances. A product can have a degradation of its expected performance during a transient disturbance but in no case should it become unsafe. Definitions of the performance levels are stated in the product family standards.
Immunity tests are required for CE marking to the EMC Directive and other European Directives. South Korea also has requirements similar to the European Union for immunity for KCC marking.
Electrostatic Discharge (ESD) Testing
Simulates electrostatic discharge events directly to the product, or to a nearby conductive surface.
European Test Standard: EN 61000-4-2
The ESD test requires that discharges be made to all exposed surfaces of the EUT, including connector backshells. Contact discharge is to the conducting surfaces of the product and air gap discharges are to non-conducting surfaces. The test also requires that contact discharges be made to a horizontal reference plane and vertical reference plane at locations 10cm from the front, rear and sides of the EUT.
Typical rise time of the ESD pulse waveform is approximately 0.7 – 1nS with a hold time of 30 – 60 nS.
Radiated Immunity Testing
Radiated RF Immunity IEC61000-4-3 immunity testing requires that the EUT (equipment under test) operates satisfactorily when subject to a strong radiated electromagnetic field. (Such as might be created by cell phones and other intentional radiators, and RF noise that might be caused, inadvertently or otherwise, by industrial processes). This requires a frequency scan at a certain fixed level of field strength (specified by the standard). The ‘scan’ will comprise a series of ‘steps’ in frequency. Each step is specified as a percentage of current frequency value. This percentage is variable from 0.2% to 5%. At each step, the frequency is held, the level adjusted to the required field strength (V/m) as measured by a field sensor, a prescribed modulation mode is initiated and then the conditions held for a ‘dwell’ time. The EUT should be monitored to detect faulty operation during the test. Typical values for field strength are 3 V/m for domestic and 10 V/m for industrial products.
European Test Standard: EN 61000-4-3
The product is placed in a nominal test field. The field is swept across the frequency range, defined in the product or generic standard and is amplitude modulated by a 1kHz sine wave (unless the product/generic standard specifies otherwise). The test field is pre-calibrated without a product in the test chamber. The test field must meet a 0 to +6dB uniformity. The test levels are 3V/m (EN50082-1) and 10V/m (EN50082-2).
The EUT is positioned so that the side under test is in the plane of the calibrated field. The test is repeated on each side of the EUT.
Performance criterion: Typically A
Electrical Fast Transients (EFT) Testing
Simulates high frequency electrical disturbance on power and signal lines due to the switching of inductive loads on the AC line.
European Test Standard: EN 61000-4-4
The test waveform consists of a 15ms burst of pulses at 300ms intervals. The pulses have a rise time of 5ns and a dwell time of 50ns, with a repetition rate of 5kHz.
Noise is directly injected onto power lines through a capacitor and capacitively coupled onto I/O lines using a coupling trench. DC power ports connected to an AC-DC power adapter are not tested.
Performance criterion: Typically B
These tests relate to the immunity requirements for equipment to unidirectional surges caused by overvoltages from switching and lightning transients. Several test levels are defined which relate to different environment and installation conditions. These requirements are developed for and are applicable to electrical and electronic equipment.
System switching transients can be separated into transients associated with :
Major power system switching disturbances, such as capacitor bank switching;
Minor switching activity near the instrumentation or load changes in the power distribution system;
Resonating circuits associated with switching devices, such as thyristors;
Various system faults, such as short circuits and arcing faults to the earthing system of the installation.
The major mechanisms by which lightning produced surge voltages are the following :
A direct lightning stroke to an external circuit (outdoor) injecting high currents producing voltages by either flowing through earth resistance of flowing through the impedance of the external circuit;
An indirect lightning stroke (i.e. a stroke between or within clouds or to nearby objects which produces electromagnetic fields) that induces voltages/currents on the conductors outside and/or inside a building;
Lightning earth current flow resulting from nearby direct-to-earth discharges coupling into the common earth paths of the earthing system of the installation.
The rapid change of voltage and flow of current which may occur when a protector is excited may couple into internal circuits.
European Test Standard: EN 61000-4-5
Test voltages of up to 4 kV are applied synchronized to the voltage phase at zero-crossing and peak value of the A.C. voltage wave (positive and negative). The surges are applied line to line and line to earth. When testing line to earth the test voltage is applied successively between each of the lines and earth. All lower levels including the selected test level is tested.
The test levels shall be selected according to the installation conditions.
All voltages of the lower test levels shall be satisfied.
Conducted Immunity Testing
Simulates disturbances created by radio transmitters operating below 80 MHz (such as AM broadcast transmitters) that would typically be coupled onto a products interface cables.
European Test Standard: EN 61000-4-6
The test signal, amplitude modulated by a 1kHz sine wave, is injected onto the AC or DC wires via a Coupling, Decoupling Network (CDN) while the frequency is varied. Unshielded cables can be tested using either a CDN, coupling clamp or current injection probe. Shielded cables are tested using direct injection, the signal is coupled through a 100-Ohm resistor onto the shield of the cable under test. The injection level is pre-calibrated using the appropriate calibration jig and is equivalent to the open circuit voltage at the output from the amplifier for an unmodulated signal.
The test level for the residential, commercial and light industrial generic standard is 3 Volts; for heavy industrial equipment the test level is 10 Volts.
Performance criterion: Typically A
Magnetic Field Immunity Testing
The magnetic fields to which equipment is subjected may influence the reliable operation of equipment and systems.
These tests are intended to demonstrate the immunity of equipment when subjected to power frequency magnetic fields related to the specific locations and installation condition of the equipment (e.g. proximity of equipment to the disturbance source). The power frequency magnetic field is generated by power frequency current in conductors or, more seldom, from other devices (e.g. leakage of transformers) in the proximity of equipment.
The EUT is subjected to a continuous magnetic field of 3 A/m or 10 A/m by use of an induction coil of standard dimensions 1m x 1m. The induction coil is then rotated by 90° in order to expose the EUT to the test field with different orientations. Three orthogonal planes are tested. The dwell time at each frequency is not less than the time necessary for the EUT to be exercised, and able to respond.
European Test Standard: EN 61000-4-8
Voltage Dips and Interruptions Testing
Electrical and electronic equipment may be affected by voltage dips, short interruptions or voltage variations of power supply.
Voltage dips and short interruptions are caused by faults in the network, in installations or by a sudden large change of load. In certain cases, two or more consecutive dips or interruptions may occur. Voltage variations are caused by the continuously varying loads connected to the network.
These phenomena are random in nature and can be characterized in terms of the deviation from the rated voltage and duration. Voltage dips and short interruptions are not always abrupt, because of the reaction time of rotating machines and protection elements connected to the power supply network. If large mains networks are disconnected (local within a plant or wide area within a region) the voltage will only decrease gradually due to the many rotating machines, which are connected to the mains networks. For a short period, the rotating machines will operate as generators sending power into the network. Some equipment is more sensitive to gradual variations in voltage than to abrupt change. Most data-processing equipment has built-in power-fail detectors in order to protect and save the data in internal memory so that after the mains voltage has been restored, the equipment will start up in the correct way. Some power-fail detectors will not react sufficiently fast on a gradual decrease of the mains voltage. Therefore, the d.c. voltage to the power-fail detector is activated and data will be lost or distorted. When the mains voltage is restored, the data-processing equipment will not be able to restart correctly before it has been re-programmed.
Consequently, different types of tests are specified to simulate the effects of abrupt change voltage, and, optionally, for the reasons explained above, a type test is specified also for gradual voltage change. This test is to be used only for particular and justified cases.
European Test Standard: EN 61000-4-11
The EUT is tested for test levels of 30%, 60% and >95% below the rated voltage for the equipment. The duration of the dips/interruptions are 10ms, 100ms and 5000ms respectively. Five dips are performed for each test level at a rate of one dip per minute. The changes in supply voltage occur at zero crossing of the voltage.
The voltages in these tests use the rated voltage for the equipment (UT) as a basis for voltage test level specification.
Temperature and Humidity Testing
CSZ’s Z-Plus 8 cu. Ft. Temperature & Humidity Test Chamber simulates a full range of temperature and humidity conditions:
|Temperature Ranges||-34°C to 190°C (-30°F to 375°F)|
|Humidity Range||10% to 98% RH|