An oscillograph measures electric current and voltage, with two main types: electromagnetic and cathode ray. It is used in engineering, telecommunications, and medicine. Electromagnetic models are simpler, while cathode ray tube displays the waveform. The instrument has progressed from a pen on a drum to digital models that can store and transmit results electronically.
An oscillograph is an instrument used to measure electric current and voltage, and in general there are two main types: electromagnetic ones and those built around cathode rays. Electromagnetic models are simpler and tend to be less common, although much depends on usage. The instrument in both its forms is used extensively in engineering, telecommunications, and medicine, virtually anywhere accurate measurements of electrical outputs are important. Technically speaking, an oscillograph differs from its oscilloscope by virtue of its ability to store and save data; Originally at least, oscilloscopes were only useful for real-time measurements and were unable to capture data points for future reference. This is usually no longer true, however, and as a result the terms are often used interchangeably.
Basic concept and main uses
There are a number of reasons people might want or need to measure electric currents on a small scale. Electronics manufacturers are a good example, and in these contexts an accurate reading of how much energy is flowing through a given device is really important for things like safety and compatibility with external outlets like power cords. Measuring the currents flowing through machine motherboards and circuit breakers in buildings and offices is also important in a number of ways. In medicine, precise measurements of the electrical charges pulsed outward by the heart can give a good indication of the health and potential problems in the arterial system. An oscillograph is a convenient and portable way of taking measurements in these and similar settings.
electromagnetic models
The electromagnetic version is a surprisingly simple tool. Current is fed through the instrument and into a magnetic coil. Small changes in the electric current cause momentum to build up in the coil. This momentum is measured and any change in current or voltage is derived from the speed and deflection of the coil.
There are two common variations of the standard electromagnetic machine; one uses lasers and the other has a direct output. When equipped with a laser, light is bounced off the laser off a curved mirror and returned to a receiver. The time it takes for the light to return is measured instead of measuring the coil directly. This makes the readings more accurate and makes it easier to see smaller changes in the current. Direct output often takes the form of one or more arms drawing wave patterns on paper as current is fed into the machine. This variation is the only form of direct output common in electromagnetic oscillographs, other forms of output are just strings of measurements that need interpretation before they are useful.
Cathode ray tube
Cathode ray oscilloscopes use a small television-like screen to show the actual wave pattern of the current as it travels through the device. When no power is supplied through the device, the CRT displays a single fixed dot or a single dot that moves vertically across the screen. When current is in motion, power moves through a series of plates that measure the change in current. The current causes these plates to fluctuate relative to each other and that motion is reflected on the screen by the dot moving up and down. This moving dot actually shows the electric current in its waveform. This allows the device to measure not only standard current like the electromagnetic model does, but also waveforms like heartbeats.
Progression and advancement
The oscillograph and accompanying oscilloscope have come a long way since their introduction into the mainstream in the early 1800s. The first was a very rudimentary model that involved a pen mounted on a drum that made waves in response to electrical stimulation. In fact, the first photographic models concerned exhibition papers, which lasted until the advent of more modern films; nearly all devices today are digital, and many are capable of storing and transmitting results electronically in real time.
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