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- About Yokogawa:
- Research & Development:
- Virtual Museum of Measurement:
- 1. Standard AC Ammeter (DLS):
- 2. Recording Meter:
- 3. 200C Audio Oscillator:
- 4. N-3 Electromagnetic Oscillograph:
- 5. A Collection of Electric Meters:
- 6. Universal Galvanometer:
- 7. Electrostatic Voltmeter:
- 8. Edison's Incandescent Lamp and Lamp Power Meter:
- 9. Circuit Testers: Past and Present:
- 10. Illuminance Meters:
- 11. Admittance Bridge:
- 6. Wife of a Rice Shopkeeper (woodblock print):
- 7. La Fee Electricite (lithograph):
- 15. Large Screen Multimedia Presentation>
- From Battery Testers to Multimeters:
- Scientific Tools and Measuring Instruments Used as Teaching:
- Yokogawa and the Electromagnetic Oscillograph:
- Learning from the Smithsonian Institution:
- Hewlett-Packard's Contributions to Our Collection:
- Yokogawa and the Electromagnetic Oscillograph
Yokogawa and the Electromagnetic Oscillograph
In a reflecting galvanometer, a small mirror is attached to a magnetic coil through which electric current is passed. This induces a magnetic field that causes the coil to rotate. By directly observing or recording on film the light that is deflected from the mirror, it is possible to measure minute variations in electrical current. The first such device was developed by Cambridge Instruments. In 1920, Westinghouse began producing a portable electromagnetic oscillograph. Similar instruments were developed by General Electric and Siemens.
As imported oscillographs were still quite expensive in the early 1920s, Japanese laboratories soon developed their own electromagnetic oscillographs and Yokogawa commenced production of this device in 1924.
This was the first portable oscillograph in Japan that could observe and record alternating current waveforms. It was in wide use in company and university laboratories all over Japan and it won honorable mention at an international technology fair in Belgium in 1930.
This combustion test chart was produced with an electromagnetic oscillograph that recorded waveforms using electrical signals received from temperature detecting plugs, a piezo-pressure transducer, and other devices connected to the diesel engine.
The heart of the measuring system in the electromagnetic oscillograph was the galvanometer mirror, a small (1 x 2 mm) vibrating element that had a thin ligament strip. Producing good waveforms under actual test conditions required great skill. This device could record high voltages, audio-frequencies, and even single transient phenomena. It also had many useful features such as an optical lever that enabled interference-free handling of multiple signals. Devices like these were in use up until the 1960s.
