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 to bring clarity to their stoppage.
e) Decrease progressively, at least 5 s, the strength of the magnetic field back to zero.
f) Remove the watch from the test apparatus.
g) The rate (M CH-1 ) shall be measured for at least 180 s in the 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 rate (M CH-1 ) is the average of instantaneous rates measured for 180 s or longer.
h) Demagnetize the watch in each of the three 3H-9H, 6H-12H and CH-FH directions.
i) Carry out steps from a) to h) also in the 6H-12H and CH-FH directions of magnetic fields application in order to define respectively the M CH-2 and M CH-3 rates. 5.3.3 Test procedure for electronic watches 5.3.3.1 Magnetic resistance test Magnetic resistance tests shall be carried out as follows:
a) Place the watch on the test apparatus for each stepper motor installed in the direction most affected by the magnetic fields.
NOTE When the most affected direction is unknown, the tester (laboratory) is responsible to determine it (e.g. turning the watch in the horizontal plane while applying the field; testing the watch 6 times every 30° in the horizontal plane and once perpendicularly).
b) Increase progressively, at least 5 s, the strength of the magnetic field to the test value (in this case 4 800 A/m)
c) Observe the watch for 60 s to confirm that the watch does not stop during magnetic field application. In the case of a stepper motor having an interval of impulses of 20 s or more, observe the running condition during five stepper motor runs. Especially for watches not equipped with a second hand, increase the magnetic field application time to bring clarity to their stoppage.
d) Decrease progressively, at least 5 s, the strength of the magnetic field back to zero.
e) Remove the watch from the test apparatus.