Ratio Tester

A ratio meter (or turns ratio meter) is designed and used to measure the turns ratio, excitation current and polarity of windings in transformers. GAOTek Ratio Meters are powerful devices that our customers can rely on to complete their every day tasks. They eliminate need for the user from having to kneel or bend down to operate the traditional ratio instruments, which speeds up the time required for each test. Unlike traditional methods, a ratio meter does not necessarily require hair springs for exerting a controlling torque, as it is being provided solely by the appropriate coil winding and non-uniform field arrangements built into the device.

Ratio meters are used to examine the turns ratio, excitation current and polarity of windings in single- and three-phase distribution and power transformers, potential & current transformers, and tapped transformers. These transformers are commonly found in the air craft industry, which makes our ratio meters even more valuable; to ensure flight is safe and air crafts are properly tested, ratio meters can test for quality and reliability. GAOTek works diligently to provide their customers with high class products that are both reliable and efficient.


Transformers change voltage through electromagnetic induction; this occurs as the flux lines (magnetic lines of force) accumulate and collapse with changes in the current passing through the primary coil, current is induced in another coil, called the secondary. The secondary voltage is calculated by multiplying the primary voltage by the ratio of the number of turns in the secondary coil to the number of turns in the primary coil; this quantity is referred to as the turns ratio.

Ratio tests are carried out on all tap positions and are calculated by dividing the induced voltage reading into the applied voltage value. For the three-phase transformer turn ratio test, the ratio is taken on one phase at a time with a three-phase TTR until the ratio measurements of all three phases are completed. The measured ratios should always be within 0.5% of the calculated ratios.

A telling ratio measurement may be made using only a few volts of excitation. The transformer should usually be excited from the highest voltage winding so as to avoid potentially unsafe high voltages. Care and caution should always be during the application of voltage and during the measurement. Real time readings of the voltmeters should always be made.

The institute of electronics and electrical engineers (IEEE for short) is a professional organization that reaffirmed standard diagnostic tests and measurements that are performed in the field on oil-immersed power transformers and regulators. The IEEE provide information is provided regarding specialized test and measuring techniques specifically related to equipment such as ratio meters (turn meters) as it is one of the main tools used in transformer voltage measurement. The IEEE standard IEEE 62:1995 (R2005) stresses that the measured ratios from ratio/turns meters should always be within at least 0.5% of calculated ratios.


GAOTek showcases high quality, great performance ratio meters at a friendly price point. GAOTek’s Ratio Meter measures the turn ratio of transformers which means the Ratio of High Voltage Winding to Low Voltage Winding of the Transformer.

The accuracy of a GAOTek ratio meter allows for repeatable tests, helping the users to determine the condition of transformers under test. GAOTek has designed a simple user interface with one button operation displaying the measured results directly on the easy to read LCD or the option to print to a printer. The following features are also aspects of our devices that may be included:

l  Single and three-phase transformer testing

l  Automatic, fast, simple user interface, rugged, lightweight

l  Our device tests various elements, including: turns ratio, excitation current, and polarity

l  Historical data search allows users to review previous data collected

l  Accessing, browsing

l  Saving and printing data

l  Dynamic display

l  High and low voltage first and secondary loop current, variable ratio, polarity, phase difference, current leakage online test; current on both sides of transformer, variable ratio online monitoring

l  Power supply is DC6V alkaline dry battery (1.5V AAA×4), continuously working for 30 hours

l  Wireless transmission; the maximum distance of straight line transmission is about 30m

l  Battery powered. When battery voltage is lower than 4.8V, battery voltage is shown in low symbol to remind user to replace the battery soon


Ratio meters are usually used by manufacturers at the end of the production process of transformers or during factory acceptance testing. Post-secondary engineering departments who are actively learning about turn ratios and its measuring principles use ratio meters. Research institutes studying and working on the fundamentals of transformers and power engineering can also use ratio meters. Perhaps more commonly, electricity companies and the air craft industry use these devices on a regular basis.

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