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What Is an Oscillograph?

Oscilloscopes are a type of oscillograph used in science, engineering and medicine.
The cathode-ray oscillograph features a cathode-ray tube similar to the one found in early television sets.
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  • Written By: M. McGee
  • Edited By: Jenn Walker
  • Last Modified Date: 19 August 2014
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An oscillograph is a tool used to measure electric current and voltage. There are two types of oscillographs commonly used today: the cathode-ray oscilloscope and the electromagnetic oscillograph. The electromagnetic oscillograph is more basic in design, featuring a simple magnetic coil and a method of measuring changes in the coil. The cathode-ray oscilloscope is more complex—even the basic model is built around a cathode-ray tube (CRT), similar to the ones found in older televisions. The oscilloscope tends to give more accurate data and is used in many fields, including science, medicine and engineering. It is commonly used in laboratory experiments, electronic equipment maintenance and troubleshooting and as a medical diagnostic tool, such as displaying the wave forms of heartbeats in an electrocardiogram. Modern models use LED or LCD screens instead of cathode-ray displays.

The electromagnetic oscillograph is a surprisingly simple tool. Current is fed through the instrument and into a magnetic coil. Slight variations in the electric current causes momentum to build in the coil. This momentum is measured and any variations in current or voltage are derived from the speed and flex of the coil.

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There are two common variants of the standard electromagnetic oscillograph; one uses lasers, and the other has a direct output. When fitted with a laser, light is bounced from the laser off a curved mirror and back to a receiver. The time it takes for the light to return is measured instead of the coil being measured directly. This makes the readings more accurate and makes it easier to see smaller variations in the current. Direct output on an oscillograph often takes the form of one or more arms drawing wave patterns on paper as the 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 oscilloscopes use a small TV-like screen to show the actual wave pattern of the current as it travels through the device. When no current is fed through the device, the CRT displays a single stationary dot or a single dot moving vertically across the screen. When current is moving, the power moves through a series of plates that measure the variation in the current. The current causes these plates to fluctuate in relation to each other, and that movement is reflected on the screen by the dot moving up and down. This moving dot is actually showing the electric current in its wave form. This allows the device to measure not only standard current like the electromagnetic oscillograph does, but also waveforms such as heart beats.

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