Conformity Magazine - November 2007 - (Page 58)

not equate to the current flowing back into the tester (iin) then the tester shuts down. It is worth noting that this safety feature will work only if the device being tested is not grounded. If the device being tested is grounded, then the current will flow to ground and not through the user, for current flows through the path of least resistance. Most testers will automatically discharge at the end of test. This is important for DC and IR testing. Automatic discharge time will vary from tester to tester; precautions should be implemented to ensure the device is discharged. If testing a highly capacitive device you may want to focus on the discharge times of the available testers. There may be significant time savings involved based on the tester you choose. Once safety has been addressed, manufacturers are interested in reducing test time. Standards play a role in the duration of the test; however, the time taken connecting to the product, executing the test and recording the data adds additional overhead that can be eliminated. As mentioned earlier, a tester that combines multiple tests in one instrument is an advantage, not just because of only having one instrument but also one connection. For instance, let’s take the three most common tests: Ground Bond, Hipot, Line Leakage or Functional Run. A manufacturer can run these tests with three individual instruments or with one. Ground Bond requires connection to the ground plug and to the casing of the product. Hipot will then require connection to the ground plug and to line and neutral. Line leakage testing is performed with ground plug and line and neutral separated. Figure 2 shows connection to a 5 in 1 tester which will allow for Ground Bond, Hipot, Insulation Resistance, Functional and Line leakage testing. Item A and B in Figure 2 are used for Ground Bond. Item B connects to the ground connection of the adapter box. Hipot is performed using Item C and B. High voltage is output from both Line and Neutral of Figure 2 Item C, and the insulation between these points and ground is tested. Because Line and Neutral are separate connections, Functional Test and Line leakage are tested with the same connection. Combining different tests in one unit is a time savings; one must also consider the points which need to be tested within the device. When a device has several points to be hipot tested, a scanner speeds up the testing process and reduces human error. For example, a typical safety test for a power line filter requires a Hipot test of all line connections to ground in addition to Hipot from line to line. This test can become time consuming when moving test leads. A scanner will allow connections to be made once, and the hipot tester will scan through each connection for the proper voltage and time. Table 1 shows the hipot test sequence for a filter. If one test point takes 60 seconds, the whole test will take 6 minutes. Using a scanner allows the operator to multitask during the 6 minutes rather than having to change test leads every minute. Time can also be saved by digitizing data. More and more manufactures are moving away from the pass/fail hipot test to actual data that provides historical records to verify their shipping safe product and to enhance process control. Newer testers digitize data directly to a PC. The testers follow customized command protocols to allow full control over the tester and its results. Software or sample programs as well as Labview Drivers are generally available for most testers on the Figure 2: Ground bond, hipot and line leakage connection Test Point C–N A–N B–N C–A C–B A–B Step # 1 2 3 4 5 6 Voltage 2.250 kV 2.250 kV 2.250 kV 2.250 kV 2.250 kV 2.250 kV High 5.0 mA 5.0 mA 5.0 mA 5.0 mA 5.0 mA 5.0 mA Time 60.0 s 60.0 s 60.0 s 60.0 s 60.0 s 60.0 s Low Off Off Off Off Off Off Arc Off Off Off Off Off Off Ramp 2.0 s 2.0 s 2.0 s 2.0 s 2.0 s 2.0 s Box1: 1 2 3 4 5 6 7 8 HXXLXXXX XHXLXXXX XXHLXXXX HLXXXXXX HXLXXXXX XHLXXXXX Table 1: Hipot Test Sequence for a Filter 58 Conformity noVEmBEr 2007

Table of Contents Feed for the Digital Edition of Conformity Magazine - November 2007

Conformity - November 2007 Contents Editor’s Note Commission Sets Date, Terms for 700 MHz Auction FCC Reaffirms Roaming Obligations Commission Moves to Improve USF Management FCC Proposes Fines for Violations of E911 Handset Requirements Commission Levies $1 Million Plus Fines for Unsolicited Fax Advertisements GR-3150 - Lithium Battery Certification Levels Based on Criteria for General Product, Safety, and Performance, Part 2 ESD Open Forum Machinery Field Evaluation for the United States Validation, Verification, and Immunity Testing Techniques for EMC for Functional Safety Thermal/EMC Simulation Addresses New Mechanical Design Challenges Product Safety Equipment Buyer’s Guide FCC Releases Report on Telephone Numbering Resource Utilization Canada Still Has PCS Spectrum to Assign Updated Standards List for the EU’s Medical Devices Directive Updated Standards List for EU Directive on Active Implantable Medical Devices Call for Papers for the 2008 EOS/ESD Symposium Announced Mobile Phone Use in Hospitals May Be Dangerous CPSC Actions in the News IEC Standards Update UL Standards Update Telcordia Standards Update From Our “You Can’t Make This Stuff Up” Department Product Reviews Looking Back: Items from Past Issues of Conformity Upcoming Events Advertisers

Conformity Magazine - November 2007

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