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DUT Output Return Relay

Introduction
The reinforced hipot test is a critical safety test required for medical electrical equipment, ensuring that the insulation system of the applied part can withstand higher voltage without breaking down. The test is required as per IEC 60601-1 Medical Electrical Equipment Standard and other related Standards, this application note introduces the “Return Relay Option” as an effective means to perform reinforced hipot testing on applied parts. In this document, we will explain the concept of reinforced hipot testing, the significance of using Return Relay Option, and its benefits in ensuring the safety and reliability of medical electrical equipment.

Reinforced Hipot Test – An Overview
A hipot test, also known as a dielectric or withstand test, evaluates the ability of insulation to withstand higher voltages then their normal rated operating voltages. During the test, a high voltage is applied between the current carrying conductors and its protective ground or other conductive parts. A reinforced hipot test is required for parts of the electrical device that require an added layer of insulation. These parts can be classified as Applied Parts and are indicated by the following symbols seen in IEC 60601-1 Standard:

Each type of applied part requires a means of protection, commonly referred to as Means of Operator Protection (MOOP) and Means of Patient Protection (MOPP), which is the degree of separation from the current carrying conductors and grounded parts of the medical equipment. The requirements can be listed as One or Two MOOP/MOPP. The objective of the reinforced hipot test is to identify any potential weakness or defects in the insulation that could pose safety risks during operations or fault conditions. Since a medical equipment can have varying levels of insulation, applying an incorrect high voltage during production line testing would unnecessarily overstress normal insulation. Care must be taken to only apply the hipot voltage across the correct insulation as required by the design of the medical equipment.

Understanding the Return Relays Option
OPT 11 - DUT Output Relay Controls (Models 8206, 8207, 8256, 8257)
This option provides additional settings to control the DUT Output L and N terminals during ACW, DCW and IR tests. When this option is installed and the DUT-HV setting is enabled in the Setup System screen an additional parameter will be available in the ACW, DCW and IR Test Parameter Settings screen. The operator can configure the DUT Output L and N terminals to O (off), H (which places them at high potential) or L (which places them at return potential). Refer to the table below for more details.

Normal Hipot Test – Mains to Ground

Figure 1: Normal Hipot Test

Figure 1, shows how a normal hipot test is performed between Mains and Chassis Ground on a medical device. The high voltage is applied to both line and neutral shorted together with the return being attached to the chassis of the medical equipment. The insulation between the Line/Neutral and chassis, shown as orange color labeled A, is being stressed at hipot voltage between 1200 to 1500 VAC.

Reinforced Hipot – Mains to Applied Part Hipot (Inaccurate Method)

Figure 2: Mains to Applied Part Hipot

Figure 2, shows a common but flawed method to perform Mains to Applied Part hipot test, between Mains and an Applied Part on a medical device. The high voltage is applied to both line and neutral shorted together with the return being attached to an applied part of the medical equipment. The insulation between the Line/Neutral and applied part is correctly being tested but this also overstress the normal insulation “A” that is only rated for 1200 – 1400 VAC. This happens because most test procedures and hipot test equipment fail to remove the chassis ground during a reinforced hipot test causing the much higher voltage to be applied across insulation that is not rated for that voltage.

Reinforced Hipot – Mains to Applied Part Hipot (Recommended Method)

Figure 3: Main To Applied Part Hipot With Return Relay Option

With the Return Relay option installed in the OMNIA II, Line and Neutral can now be set to a Return point. Figure 3, shows an improved method to perform the Mains to Applied Part hipot test. In this setup the high voltage is applied to the applied part and return is connected to Line and Neutral. This allows the insulation C, B and A tested without overstressing A due to the Return being connected to Line and Neutral.

Benefits of the Return Relays Option
The main benefit of the return relay option is improved accuracy, this option would allow the correct reinforced insulation to be tested without overstressing the normal insulation. This option also allows for more simplified testing process by removing the need for a test operator to manually select high voltage testing points. This can not only lead to errors in testing but could potentially damage the product being tested.

Conclusion
IEC 60601-1 Medical Electrical Equipment standard provides requirement of insulating material that provides protection for both a patient and operator. These requirements involve carefully creating insulation diagram for a medical electrical equipment that is being designed and tested by manufacturers. Since an equipment can have many different types of insulation and the location of each insulation vary, it is very important to carefully apply the correct test voltage in order not to overstress other parts of the insulation. Return Relay option provides an effective means to perform hipot tests without any needs for operator involvement and overstressing normal insulation.