|
| Electrical measuring instruments first came into use in the years after the Industrial Revolution, with the development of the railroads and the introduction of the telegraph. The origins of both basic galvanometers and Wheatstone bridges date from that time.
|
|
|
|
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.
|
|
N-3 Electromagnetic Oscillograph (30 x 100 x 50 cm)Developed by Yokogawa in 1927.
|
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.
|
|
Chart showing results from a combustion test of a 4-cycle diesel engine
|
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.
|
|
Model N-2 Electromagnetic Oscillograph (2-elements) (25 x 12 x 16 cm) Developed by Yokogawa in 1937.
|
| The N-2 electromagnetic oscillograph was a highly compact device. It could be powered by either an alternating or direct current power source, and it had a rugged two-element vibrator. To record waveforms, the observation window could be replaced with a small drum. |
|
Teaching oscillograph (56 x 20 x 40 mm) Manufactured by Yokogawa in 1930. From the collection of the Communications Museum of Japan.
|
| This instrument had a large rotating mirror (24 x 4 cm) that could project images on a 1x2m screen. |
|
Electromagnetic Oscillograph (24 elements), Model 2932 Photocorder (43 x 45 x 20 cm). Yokogawa Electric began production of this device in 1977.
|
| Ultraviolet rays from a high-pressure mercury-vapor lamp were used as the light source. This instrument did not require sensitive photographic paper. Researchers were freed from darkroom work, and the vibrator was changed to a replaceable plug-in model. |
|
|
|
|
