Electrical Safety Compliance Test
“Electrical Safety Compliance Testing" is a topic which comprises all test procedures that are conducted during product validation as well as during on-going production, and which serve to ascertain the safety of the operator during operation of the product. These tests are always of relevance whenever a product has a supply voltage of 60VDC or 25VAC or above, or when it is capable of emitting voltages which may be potentially dangerous to the operator. The testers which are used to perform electrical safety compliance tests are referred to as "VDE Testers" by many of our customers.
There are different standards in place for the various markets and product categories (e. g. EN, IEEE, UL, CSA); these describe the required tests in every detail. A table which maps the test devices to the relevant standards is available under the Associated Research Safety Standard Reference Chart.
There is a further field of application for the equipment described in this section, namely material testing; one example for this is the verification of the dielectric strength of insulating materials.
The applicable test methods can be divided into the following categories:
High Voltage Test
High Voltage Testing is also known as "Hipot Testing", "HV Testing" or "Dielectric Withstand Testing". During this test, the DUT is submitted to a high AC or DC voltage, and the ensuing leakage current is then measured. When the insulation barrier breaks down, a large current will suddenly start to flow, which will only be limited by the test device. The HV testers we distribute feature a configurable current limit, at which the device is switched off in case of a breakthrough.
The current which the test device is able to deliver can be of particular importance for AC high voltage testing. A certain leakage current will always occur when the load of the filter capacitors in the DUT's power supply is reversed; this current has to be supplied by the test device in order to achieve the configured test voltage. Some standards require devices which can deliver up to 500VA.
Insulation Resistance Measurement
Insulation resistance measurement is a special case of high-voltage testing. During this measurement, the applied voltage and the resulting current are used to calculate the insulation resistance. The insulation resistance is usually tested at voltages of up to 1kV.
Ground Bond Test / PE Conductor Test / Ground Continuity
Ground Bond Tests are conducted in order to verify the grounding of DUTs which are categorized as Protection Class 1. These devices feature an electrical connection between body parts and/or internal components and the protective earth (PE) of the mains connection. The PE is tested with respect to low resistance and current-carrying capability. Depending on the applicable standard, it may be necessary to perform a "Ground Continuity Check"; during this test, a defined current (typically <1A) is applied, and the contact resistance is measured. The so-called "Ground Bond Test" has even higher requirements. During this test, the ground connection is subjected to a current which is higher than the highest current which could occur during a failure of the device. Common requirements for this test define currents of 30-40A; in exceptional cases, up to 60A may be required. The DUT is subjected to the current over a specific time period (dwell time); this time is calculated such that an insufficient ground connection can be destroyed by the current, which will cause the contact resistance to rise accordingly.
Multifunction Safety Tester: Leakage Testing
Leakage current tests are usually performed under normal operating conditions of the DUT, often at an increased operating voltage. The leakage current that may flow via the operator or the protective earth is measured under various failure conditions; it may not exceed the limits defined in the relevant standard. The following failure conditions are tested in all possible combinations:
- Normal operating conditions
- Interrupted connection to protective earth
- Interrupted connection to N conductor
- N and L reversed
For medical electronic devices, it is necessary to perform additional testing of leakage currents via the patient connections (e. g. ECG electrodes), as well as a verification of the leakage currents between two patient-connected devices (mains on applied parts).
The tester's integrated line-leakage module, where appropriate in combination with external HV switching devices, provides the necessary signal paths and the connecting circuitry for the tissue replications that are required by the respective standards. An equivalent leakage current will flow, which depends on the selected tissue replication.
The power supply for the DUT can either be provided by an external AC source or by the tester itself. For this purpose, the Associated Research devices, Omnia II 8207 and 8257, are equipped with an integrated 500VA AC source. The usage of an AC source has the advantage of providing a configurable supply voltage and mains frequency, which can be programmed according to the requirements of the relevant international standards.
Functional Test at Operating Voltage / Functional Run Test
After completion of the safety-relevant tests described above, a functional test of the DUT is usually performed at its operating voltage. The goal of this test is to unveil any damages that may have been caused by the previous tests. Normally, this test will include measurements of the current consumption as well as the power factor.
High Voltage Test Enclosure
Standard EN50191, "Erection and operation of electrical test equipment", describes the workplace design requirements for test stations where hazardous voltages are present.
This standard is relevant for voltages >60V DC or >25V AC and
- currents above 3mA AC or 12mA DC
- stored electrical energy >350mJ
To assist with the design of these workplaces, LXinstruments has developed HV test trolleys and test cages with the relevant safety equipment, as well as other accessories for safe workplace design. The test hoods are made of stable and highly isolating plastic and are closed by a swiveling transparent hood. The built-in safety switch is used to lock the hood and to disconnect the high voltage sources. This helps to ensure that no high voltage is active when the hood is open. Located in the bottom of the test cage there is a generously dimensioned space for wiring. An exchangeable adapter plate in the hood – optionally with interchangeable interface or changeable adapter kit – allows a quick adjustment for different types of DUT.
Video showing the handling of the changeable adapter kit
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