BS ISO 764:2020 pdf download – Horology — Magnetic resistant watches

BS ISO 764:2020 pdf download – Horology — Magnetic resistant watches 5.2 Test apparatus The test apparatus used shall produce homogeneous and continuous direct current magnetic fields of the test value according to the directions specified in 5.3. Admissible variations in magnetic fields strength during the magnetic resistance test shall be 0 % to +5 %. 5.3 Test procedure 5.3.1 General Flowcharts summarizing these procedures (5.3.2 and 5.3.3) are described in Annex B. 5.3.2 Test procedure for mechanical watches 5.3.2.1 Preparation before magnetic resistance test For mechanical watches, the following procedures are performed before magnetic resistance test. 5.3.2.1.1 Demagnetization A demagnetization of the watch is required in order to take into account a possible effect on the rate by repeated magnetizations and demagnetizations. The watch shall be demagnetized in each of the three 3H-9H, 6H-12H and CH-FH directions. 5.3.2.1.2 Winding At least 1 h before the initial rate measurement, the watch shall be completely winded up. 5.3.2.1.3 Measurement of the initial rate M CH-0 A measurement of the initial rate shall be carried out prior to applying any magnetic field. Switchable mechanisms shall be stopped and the hands, the date and other mechanisms shall be set up such to avoid any disturbance during the rate measurement. The rate shall be measured during at least 180 s in CH position, according to ISO 3158, by using a rate measurement apparatus. This duration shall be increased if necessary, based on the stability and periodicity of the rate. The initial rate (M CH-0 ) is the average of instantaneous rates measured for 180 s or longer. 5.3.2.2 Magnetic resistance test Magnetic resistance tests shall be carried out as follows: a) Switchable mechanisms shall be stopped and the hands, the date and other mechanisms shall be set up such to avoid any disturbance during the rate measurement and magnetic fields application. b) Place the watch on the test apparatus so that the magnetic field is applied in the 3H-9H direction parallel to the watch face. c) Increase progressively, at least 5 s, the strength of the magnetic field to the test value (in this case 4 800 A/m). d) Observe the watch for 60 s to confirm that the watch does not stop during magnetic field application. Especially for watches not equipped with a second hand and with the spring balance oscillator not visible in the testing position, increase the magnetic field application time...