Source google image: https://1.bp.blogspot.com/-XzTQMzJFZ8c/Td3zn-uW4wI/AAAAAAAADcs/BuUnbMntSIo/s1600/fig11.jpg
Schema électrique frequencemetre
Source google image: https://1.bp.blogspot.com/-XzTQMzJFZ8c/Td3zn-uW4wI/AAAAAAAADcs/BuUnbMntSIo/s1600/fig11.jpg