Patent GB-1168150-A (GB)
Title: Improvements in or relating to methods of Testing Apparatus
Inventor: MEHNERT WALTER ERICH
IPC: G01R31/00
Filed: 1967-12-06
Abstract: 1,168,150. Testing electrical apparatus. ENTWICKLUNGSRING SUD G.m.b.H. Dec. 6, 1967 [Dec. 22, 1966], No.55582/67. Heading G1U. [Also in Division G3] In testing apparatus whose inputs and outputs are represented by electrical signals, a series of input test signals are stored, then fed to a master sample whose outputs, together with the input signals, are stored together with information and instructions for programming the subsequent test operation and calculating the results, then the test input signals are fed to apparatus to be tested and the outputs of the latter are compared with the output of the master sample in evaluation circuitry according to the previously stored instructions. Tolerances are calculated from the master sample output, or alternatively, a number of samples may be used to find a suitable range of values according to which the tested apparatus may be said to function correctly. Frequency modulated input test signals are fed from a first magnetic tape 10, Fig. 1, through a demodulator 20 and matching unit 30 to a master sample 60. The outputs of the latter are fed through a further matching unit 70 to a modulator 40 and together with the input signals from the modulator 20 are recorded on a second tape 51. The units 80, 90 serve for recording information for conducting the test and evaluating the results. For the actual test operation, Fig 2 (not shown) the master sample is replaced by the apparatus to be tested, and the modulator 40 and tape recorder 50 are replaced by an evaluation and comparison unit (100), a digital computer (101) and an output unit (106) which provides information as to the type and location of any fault in the tested apparatus. The output signals of the sample and tested apparatus are compared as to frequency, phase, amplitude and their differential co-efficients of the first and second order. To help determine the test step and corresponding input signal at which a fault occurs, the input signal and master sample output signal are provided with a time code. The frequencies are measured by counting the zero crossings per unit time or measuring the time between two zero crossings and the frequencies are compared by analogue or digital subtraction. The phases are compared by measuring the angle between two vectors representing the output of the master sample and the tested apparatus. Alternatively both outputs are multiplied by a sine and cosine function and the resultant function integrated between the limits of the observation period. The phase differences between the resultant functions and the beginning of the observation period, and hence between the two output signals, are thereby obtained. The amplitudes are determined by comparing the integrals of the output signals over the observation period, the integration being controlled by the phase determination so that phase displacement does not introduce errors when comparing amplitudes. A plurality of test points may be provided in the master sample so that a matrix of values may be determined to assist in the classifying and locating of faults in the tested apparatus.