VIRTUAL INSTRUMENT AND FREQUENCY CONVERSION TECHNOLOGY-BASED BRAKE TEST SYSTEMBrake is widely useful and very important safety assuring equipment. The aim of Brake test system， which is based on visual instrument and frequency changing technology， is to integrative measure and analyze the performance and quality of the brake.This paper mainly introduces the principle， composing，function and features of the brake test system. And from the point of view of the principle of Visual Instrument （VI） technology， a test system， based on the VI and frequency changing technologies and consist of frequency changing drive and control sub-system and measuring sub-one， is constructed. With the test system the performances and braking course could be auto controlled and measured to the brakes which includes disc and drum ones. And the measuring and control software is programmed with the LabVIEW published by American NI Corporation， USA.Then data real time acquisition， processing， displaying and recording will be realized. The test system also has the functions of voltage adjusting， rotating speed control， load regulating， JC value setting， temperature measuring， and braking route and time memorizing and analyzing. It will be very important for meaning and exciting boosting effect to advance quality and capabilities of the brakes and the security of equipments and system which have adopt the brakes.1 Operating principlesAccording to the principle of work and power， the change of kinetic energy in the moving of objects equals to the full power of the force act on the object in that process.The energy obtained by brake to be tested：Therefore， it is feasible to use combined inertial flywheels to simulate rotating inertia of crane hoist and its transmission components to test the performance and quality of the brake.According to the moment of momentum theorem：Tbt =Ji （1）When Tb is fixed， tb can be controlled through combinations between Ji and differently. Brake drum or plate， which will be measured， and combined inertial flywheels for loading on are driven to rotate by AC frequency conversion motor （or DC one， which will not bedealt with in this article carefully）. According to the principles shown in the formula （1） ， we can simulate actual processes of brakes fitted on lifting and transport machineries， engineering ones， mining ones and construction ones by changing the technical specification duty JC， the flywheels inertial moment Ji and motors rotational speed ni.When detected brakes work in simulation cycle and brake repeated， infrared thermoscopes and torque sensors， and other sensors will record braking shown in the heat， braking torque，braking time and brake speed parameters.2The composition and structure of the brake test systemThis test system is intended to achieve the performances of drum and disc brakes and has following functions：（1） Brake replacementAccording to different type of brakes the corresponding base will be chosen and brake position could be adjusted using electric slide test-bed；（2） Multi-level loadingWe can simulate the actual loading on brakes in a crane with different combined flywheels. The test system adopts manual hydraulic system composed by a three-position four-way hand-operated direction valve， a relief one and their accessories， and it is operation saving and convenient to replace flywheels.（3） Regulation the rotational speed n （or ）It can be realized by changing frequency supplied to the AC motor. When braking torque is very large， such as 10000Nm， it should be appropriate for regulating initial brake speed upward 1000r/min to minimize rotating inertia possibly.（4） Braking frequency adjustmentBased on actual needs braking frequency can be confined in a range of 14 times per minute.（5） Braking torque measurementThere are three methods：a） Direct measurement via torque sensors：Rotational speed and torque sensor will be installed between the detected brake drum or plate and inertial flywheel plates.Dynamic braking torque of detected brake will be directly measured， shown in Fig.1 and Fig.2. According to the scope of braking torque of detected brakes， two or three rotational speed and torque sensors should be prepared for testing torque to meet the accuracy requirements；b） Indirect parameter measurement：Based on the rotating inertia and braking time we can get brake torque using mathematical relationship between these parameters， as shown in Fig. 2.c） Indirect measurement by pedestal-force：The pressure sensors are installed under the base where detected brake are fixed to feel the forces given by brake， and then to obtain brake torque.The second approach has small investment， simple structure and no torque sensors which mean not considering related troubles of changing torque sensors. But the procedure tocalculate torque is complex， and accumulating total errors would be larger and then the result accuracy will be low.The third