ASTM-A804/A804M:04(R2021) pdf free download – Standard Test Methods for Alternating-Current Magnetic Properties of Materials at ,1 Power Frequencies Using Sheet-Type Test Specimens.
7.6.2 Electronic Digital Wattmeter—Electronic digital watt- meters have been developed that have proven satisfactory for use under the provisions of this test method. Usage of a suitable electronic digital wattrneler is permitted as an alternative to an electrodynarnometer waitmeter in this test method. An electronic digital wattmeter oftentimes is preferred in this test method because of its digital readout and its capability for direct interfacing with electronic data acquisition systems.
7.6.2.1 The voltage input circuitry of the electronic digital wattmeter must have an input impedance sufficiently high that connection of the circuitry, during testing, to the secondary winding of the test fixture does not change the terminal voltage of the secondary by more than 0.05 %. Also the voltage input circuitry must be capable of accepting the maximum peak voltage that is induced in the secondary winding during testing.
7.6.2.2 The current input circuitry of the electronic digital wattmeter must have an input impedance of no more than 1 2. Preferably the input impedance should be no more than 0. 1 2 if the flux waveform distortion otherwise tends to be excessive. Also the current input circuitry must be capable of accepting the maximum rms current and the maximum peak culTent drawn by the primary winding of the test fixture when core loss tests are being performed. In particular. since the primary current will be very nonsinusoidal (peaked) if core-loss tests are performed on a specimen at magnetic flux densities above the knee of the magnetization curve, the crest factor capability of the current input circuitry should be three or more.
7.7 Devices for Peak-Current Measurement—A means of determining the peak value of the exciting current is required if an evaluation of peak permeability is to be made by the peak-current method.
7.7.1 An air-core mutual inductor and a flux voltmeter compnse the apparatus most frequently used to measure peak exciting current. Use of this apparatus is based on the same theoretical considerations that indicate the use of a flux voltmeter on the secondary of the test fixture to measure the peak magnetic flux density; namely, that when a flux voltmeter is connected to a test coil, the flux voltmeter indications arc proportional to the peak value of the flux linking the coil. In the case of an air-core mutual inductor, the peak value of flux (and hence the indications of the flux voltmeter connected to its secondary winding) will be proportional to the peak value of its primary current. A mutual inductor used for this purpose must have reasonably low primary impedance so that its insertion will not materially affect the primary circuit conditions and yet must have sufficiently high mutual inductance to provide a satisfactorily high voltage to the flux voltmeter for primary currents corresponding to the desired range in peak magnetic field strength. The mutual inductor secondary impedance should he low if any significant secondary current is drawn by a low impedance flux voltmeter. The addition of the flux voltmeter should not change the mutual inductor secondary terminal voltage by more than 0.25 %. It is important that the mutual inductor be located in the test equipment in such a position that its windings will not be linked by ac leakage flux from other apparatus.