Testing Power Supplies for Medical Electronics Applications

Transcription

1 white pƒper Testing Power Supplies for Medical Electronics Applications g Introduction The international stard IEC specifies testing performance for electrical devices used in medical applications. This stard has undergone some significant changes in the last number of years, with the recent adoption of the 3rd edition of the stard in In fact, IEC recently announced the planned introduction of the 4th edition of the IEC60601 stard, slated for adoption in 2018, making it a design consideration for the next generation of medical equipment. The medical electronics end-product is the applied part that must be evaluated for overall performance to meet stard s requirements. The power supply is considered a component of a medical device. Although a power supply cannot be certified, it can be designed tested to meet the necessary levels of performance according to the applied part s intended applications. Testing power supplies to this medical stard can help manufacturers optimize their medical designs to achieve the highest performance safety levels thereby enable first-pass success during agency approvals. This paper describes how Excelsys Technologies Xsolo power supplies have been designed tested to meet both the B BF type requirements per the IEC stard. g Safety Classifications for Medical Applied Parts In July 2014, the IEC updated the medical stard IEC as related to Medical Electrical Equipment Part 1-2: General Requirements for Basic Safety Essential Performance Collateral Stard: Electromagnetic Disturbances Requirements Tests. The stard cites three classifications for meeting these requirements: CF, BF, B. The requirements for leakage current for each of these classifications, taken from the IEC specifications, are shown in Tables 1 2 on the following page. The CF, or Cardiac Floating, is the most deming performance level. Applied parts falling under this rating have application in products including, but not limited to, ventricular assist devices (VADs) or dialysis machines. In these applications, electrical connection can be made directly to the patient s heart during the operation of the device. Type BF or Body Floating is less stringent than CF is intended for applied parts which have conductive longterm contact with a patient. These products can include incubators, patient heating cooling equipment, ultrasound monitoring, cardiac monitoring, long term diagnostic equipment blood pressure monitoring to name a few. The least stringent requirement is for the type B, or Body, classification is reserved for applied parts that are not conductive can be immediately released from the patient. This includes, but is not limited to, LED lighting, medical lasers, medical imaging, hospital beds phototherapy equipment. Another difference between Type B, BF CF, is that type B applied parts may be 1

2 Table 1. Allowable values of PATIENT LEAKAGE CURRENTS PATIENT AUXILIARY CURRENTS (in µa) under NORMAL CONDITION SINGLE FAULT CONDITION Type b Type bf Type cf applied part applied part applied part Measuring Current Description Reference circuit nc sfc nc sfc nc sfc PATIENT Figure 19 dc AUXILIARY CURRENT ac PATIENT From PATIENT (a) dc LEAKAGE CONNECTION CURRENT to earth ac Caused by (c) Figure 17 dc an external voltage on ac a SIP/SOP Total PATIENT With the same types (a) dc LEAKAGE of APPLIED PART (h) Figure 20 ac 500 1, , CURRENT a connected together Caused by (c) Figure 17 dc an external voltage on (h) Figure 20 ac 500 1, , a SIP/SOP Table 1: Leakage current requirements according to specification: IEC , Table 3 - Reference: (a). Key: = NORMAL CONDITION; = SINGLE FAULT CONDITION Table 2. Allowable values of PATIENT LEAKAGE CURRENTS (in µa) under the special test conditions identified in Measuring Type b Type bf Type cf Current Description a Reference circuit applied part applied part applied part PATIENT Caused by an external voltage (b) Not applicable 5, LEAKAGE on the PATIENT CURRENT CONNECTION of an F f-type APPLIED PART Caused by an (d) Figure c external voltage on a metal ACCESSIBLE part not PROTECTIVELY earthed Total PATIENT Caused by an external voltage (b) Not applicable 5, LEAKAGE on the PATIENT (h) Figure 20 CURRENT b CONNECTION of an F f-type APPLIED PART Caused by an (d) Figure 18 1,000 1,000 c external voltage on a metal ACCESSIBLE (h) Figure 20 part not PROTECTIVELY earthed Table 2: Leakage current requirements according to specification: IEC Table 4 - Reference: (b). a b c The condition referred to in Table IV of the seond edition as MAINS VOLTAGE ON APPLIED PART, treated in that edition as a SINGLE FAULT CONDITION, is treated in this edition as a special test condition. The test with MAXIMUM MAINS VOLTAGE on a non-protectively EARTHED ACCESSIBLE PART is also a special test condition, but the allowable values are the same as for SINGLE FAULT CONDITION. See also the rationales for (d). Total PATIENT LEAKAGE CURRENT values are only applicable to equipment having multiple APPLIED PARTS. See (h). the individual APPLIED PARTS shall comply with the PATIENT LEAKAGE CURRENT values. This condition is not tested with TYPE CF APPLIED PARTS because it is covered by the test with MAXIMUM MAINS VOLTAGE on the APPLIED PART. See also the rationale for (D). 2

3 connected to earth ground. Type BF CF are not connected to earth ground this is why the specification refers to them as floating. g Testing Power Supplies to the Medical Stard Excelsys Technologies developed its XS series of power supplies for medical applications. Testing the power supplies to the stard was undertaken using both its basic low-leakage models, the XS N-000 XS N-004, respectively. The high efficiency XS1000 Power Supply delivers up to 1008W in an enclosed, fan cooled chassis. Nominal output voltages are 24V 48V with wide adjustment ranges user defined set points. Xsolo carries dual safety certification, EN nd Edition for Industrial Applications EN nd 3rd Edition for Medical Applications, meeting the stringent creepage clearance requirements, 4KV ac isolation <300uA leakage current. Boasting up to 92% efficiency, the Figure 1. Excelsys model XS1000 has been design tested for medical applications. XS1000 is ideal for use in acoustically-sensitive medical applications, harsh industrial environments, laboratory equipment HI-Rel/MIL-COTS applications. Excelsys used the isolation voltage ratings of each power supply to determine which one would be suitable for a particular application type (Table 3). Power supplies vary widely in terms quality reliability. There are design differences, depending on the supplier, many power supplies are not meant for medical applications. Type Input to Output Isolation Input to Ground Isolation Output to Ground Isolation B rated 4000V ac 1500V ac 500V ac BF/FC rated 4000V ac 1500V ac 1500V ac Table 3. Isolation voltages necessary for B, BF, or CF rated power supplies. g Testing Results The Excelsys testing procedures were performed in accordance with the IEC requirements using an ac source providing 264V ac at 63 Hz, which demonstrates worse-case conditions. The power supplies were tested to Tables specified by the IEC s specifications, as shown in Figures 2 3 on the following pages. The resulting data from Excelsys is shown in Tables 4 5 along with the requirements in the specification showing the limits for ac testing. These results indicate that the Xsolo products would be well-suited to either type BF or B applied applications. 3

4 Test 1: Patient Connection to Earth Result: PASS For the first test, Excelsys used the following power supply settings: Vin = 264V rms (maximum rated input voltage), Frequency = 63Hz (maximum rated input frequency) The test method was to follow the instructions shown in Figure 2 (based on IEC Fig 15.) Key Measure (with S 7 closed, if CLASS I ME EQUIPMENT) under all possible combinations of positions of S 1, S 5, S 10, S 13. S 1 open is SINGLE FAULT CONDITION. CLASS I ME EQUIPMENT only: Measure with S 7 open (SINGLE FAULT CONDITION) with S 1 closed under all possible combinations of S 5, S 10, S 13. For CLASS II ME EQUIPMENT, the PROTECTIVE EARTH CONNECTION S 7 are not used. Figure 2. (From IEC ). Measure circuit for patient leakage current from patient connection to earth. P 1 Excelsys measured the following parameters shown in Table 4: Measuring Test Condition XS N-000 XS N-004 Circuit (µa) (µa) S7 Open (Neutral) Vo- Vo+ Vo- Vo S5 Closed Reversed Input Polarity: S1 Open (Live) Table 4. Excelsys power supply test against IEC Table 15. Result: Pass. 4

5 Test 2: Patient Connection of an F-Type Applied Part Result: Pass For the second test, Excelsys used the following power supply settings: Vin = 264V rms (maximum rated input voltage), Frequency = 63Hz (maximum rated input frequency) Figure 3. (From IEC ). Measure circuit patient leakage current caused by an external voltage on the patient connection of an F-type applied part. The test method was to follow the instructions shown in Figure 3 (based on IEC Fig 16.) For legends, see Table 5. Key Measure (with S 7 closed, if CLASS I ME EQUIPMENT) with S1, closed under all possible combinations of positions of S 5, S 9, S 10, S 13. For CLASS II ME EQUIPMENT, the PROTECTIVE EARTH CONNECTION S 5 are not used. Excelsys measured the following parameters shown in Table 5: Measuring Test Condition XS N-000 XS N-004 Circuit (µa) (µa) S1 Open (Neutral) Vo- Vo+ Vo- Vo S5 Closed Reversed Input Polarity: S1 Open (Live) Table 5. Excelsys power supply test against IEC Table 16: Result: Pass. 5

6 g Summary Excelsys Technologies Xsolo power supplies have been designed tested to demonstrate that they are suitable for use in products intended for medical applications requiring compliance with either the B or BF classification. Moreover, It is not uncommon for applied products requiring type CF performance levels to need additional isolation methods such as isolated power converters in the system or medically-rated high-isolation transformers in the overall system design. Excelsys offers low leakage power supply versions, which enable incorporation of multiple power supplies into various medical-rated systems depending on the applications. Excelsys has a global applications team available to support assist customers with their system applications. References: Excelsys Technologies Ltd Excelsys Technologies Ltd 6