As history reason, different countries and areas adopt different standard for their power supply.This determines exporting products which need to have a wide range otherwise it can’t meet different specification in different areas.Thus,in order to meet different request in the world,many electronic products have a wide power adapter which can accept 110V-240V voltage.
The first power specification is created as 110V/60Hz by Nikola Tesla.Later Europe introduced the design,but changed the power specification into 220V/50Hz. Thus, in present world, there are two main power system: 100V-130V and 220V-240V. 100V and 110-130V are regarded as low voltage, used in U.S.A,Japan,boat,etc, 220V-240V is regarded as high voltage,and China and Europe use this power specification.In these countries, some of them also use 110-130V, e.g. Russia, Sweden.
100V: South Korea, Japan
110V-130V: China TaiWan,U.S.A,Canada,Mexico,Panama,Cuba,etc about 30 countries.
220V-240V: China, Hongkong (200V),U.K.,Germany,France,Italy,Australia,India,Singapore,Thailand,Holland,Spain,Greece,Austria,etc about 120 countries.
The countries using voltage of 230V-240V can almost use electrical appliance made from China,because the Max voltage in China can reach 250V.
For ultrasonic flow meter, we need to pay much attention to the power supply,otherwise flow meters may be damaged.Thus it is necessary to learn the power and frequency specification in different countries.