international eletro-magnetics


	About IEM Coil Testing: From Bench Top to Integrated Systems IEM is an engineering oriented company located in Palatine, Illinois. We have been producing bench top test equipment for the coil winding industry since 1976. Our staff includes engineers with backgrounds in magnetic field modeling and process control engineering. International Electro-Magnetics has focused on the development equipment with easily used features and reliable design. Interaction with our customers has allowed us to refine ideas for product improvement and has led to a series of innovations in its product offering. The growth of the IEM line of coil test equipment has been a natural progression. Each new product has been an extension of technology used in previous designs. Our traditional product line consists of turns counters for both bobbin and toroidal coils, shorted turns testers for bobbin coils and transformer ratiometers. By applying a modular approach to circuit designs, work done in one system can be used in other products as well. This has allowed the construction of integrated test systems that provide complete testing capability at one station. As we have developed our product line, we have tried to focus on the needs of our customers. Custom design capabilities, and a familiarity with magnetic materials and design principles, have allowed us to develop products that are both easy to use and effective production tools. Our strategy has been to offer equipment that can be used by production personnel without extensive technical training. This has resulted in a series of single purpose, bench top testers that provide accuracy and reliability. The STT-4 Shorted Turns Tester for Bobbin Coils was IEM's first coil test product and is familiar to many people in the coil winding industry. The first units were produced in 1980, and it has enjoyed steady success ever since. Because the STT-4 detects a shorted turns condition in coil windings by means of inductive coupling, testing can be done very quickly, without making electrical contact with the coil. It provides an efficient way to detect quality problems caused by defective wire insulation, winding abrasion and thermal stress. Its simplicity of use and durability, make the STT-4 ideal for testing at each winding station in work group environments. It allows defects to be detected before additional assembly is done to defective coils. A bobbin coil turns counter was a logical product development for us. Many of the same coil manufacturers that use the STT-4 also need to verify the turns count of their windings. The basic principle involved, inductive coupling of a coil to a magnetic field, is similar to that used in the shorted turns test. In its simplest form, a turns counter is comprised of a signal generator that energizes a probe and a voltmeter that measures the voltage induced in the winding. The probe itself must provide an energizing field that is both stable and of uniform flux density. Because the voltage induced in a coil for a given field strength is proportionate to its number of turns, the counter circuit is basically a voltmeter. In order to meet the accuracy required for a production tester, typically within 1 turn in 200 or .5%, both the probe drive and voltmeter circuits must be very stable. The TC-5 is able to provide repeatable measurements within .05% or 1 turn in 2,000. The development of our "Calibration" probe technology and the application of microprocessor technology has allowed the TC-5A Turns Counter to offer these features. Our Calibration Series probes offer compact design and accuracy over a wide range of coil sizes. By using a micro-processor controlled voltmeter, we can maintain stable measurements over a wide range of turn counts and temperature. Interface to the RS-232 data buss is now available as well. The TC-5A can be used without reliance on "production standards" and does not require recalibration for varying coil sizes and types. These features make it very useful for turns count verification in a production environment. IEM offers two additional types of bench top testers: the Model 1000 series Toroidal Turns Analyzer and the TR-10 Transformer Ratiometer. The Model 1000 tests for the number of turns in a toroidal winding by means of a single turn test loop that is incorporated in its test fixture. It automatically compensates for variations in core permeabilities. The Model 1000 is available in a number of configurations. We now offer features such as selectable frequency, which allows testing of both laminated and ferrite cores, and units optimized for each type of toroidal core material. The TR-10 Transformer Ratiometer will measure up to 10 individual windings; a 4 channel version that will be useful for switching power supply and lighting ballast manufacturers is planned. Switching between channels is relay controlled, making the instrument readily interfaced to computer control. Test fixtures can be readily interchanged via a card edge connector. Both automatic Ratio and manual Turn Count modes are provided to allow flexibility. Multiple test frequencies may be selected from the front panel. As we have added instruments to our product offering, we have continued to implement product improvements. Integrated circuit and micro processor designs continue to advance. As we incorporate these improvements into our products, we have always supported our customer base; upgrades to current revision levels are offered at nominal costs to our customers. It speaks well for our products' design integrity to say that many of our customers prefer to use our equipment in its original configuration. It is not unusual for us to receive units for repair that have been in regular use for 10 years or more. We recognize the importance of reliability and ruggedness to our customers. Automated Test Systems We are now applying the lessons that we have learned in building bench top testers to the integration of computer based test systems. Although single purpose testers continue to have an important place in the design and production of magnetic components, integrated systems that combine multiple tests at one station can offer an improvement in production efficiency. There is a general trend, particularly among large volume manufacturers, to utilize the efficiencies of automated testing stations. By using standardized test modules, it is possible to configure each test system to the requirements of individual customers. Password protection and part number/job number entry is easily configured to meet the customer's existing scheme. Our approach to automated testing systems has been to provide visually oriented menus that allow testing personnel to easily select and setup testing configurations. A sample window from our HV-2 test system for transformers is shown in fig. 2. Primary and secondary windings are represented schematically and are selected by clicking a mouse button. Turn counts are manually entered and ratios are then computed by the system. Additional setup windows allow the test operator to select tests to be performed and test parameters and tolerances. All test connections of the HV-2 are done through a logic controlled switching matrix designed by IEM. The matrix is composed of a series of 8 channel modules. Tests are performed in an order that allows defective parts to be rejected early in the testing sequence. Resistance and polarity tests confirm that windings are properly connected. If the system detects errors at this point, it will reject the transformer without further testing, allowing the operator to determine whether to correct the fault or to continue on to the next unit. Induced potential (Hipot) and applied potential tests, which take significant time, are placed later in the test sequence. Safety interlocks are provided to help restrict access to the test connections when power is being applied to the transformer. A variety of safety features can be connected to the system, depending on the requirements of the customer. By using a modular construction, many variations are possible. In addition to test systems built by us, IEM has also begun to offer Surge Testers, Wound Stator Bonding Systems and other equipment designed and produced by HPT, an Italian design company. This cooperative effort will allow us to offer products suited to the motor manufacturing industry. Although many things have changed since our first shorted turns tester in 1976, we hope to continue to provide a source for effective test equipment. We realize that our own success is dependent upon that of our customers. Only by understanding your requirements can we hope to offer effective testing solutions.