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Glossary / Dictionary of Electronics Terms - O

octave - Interval between two sounds whose fundamental frequencies differ by a ratio of 2 to 1. 440 Hz. is one octave above 220 Hz.

offset null - An op amp control pin used to eliminate the effects of internal component voltages on the output of the device.

ohm - Unit of resistance symbolized by the Greek capital letter omega (W).

ohmmeter - Device used to measure electrical resistance.

Ohm's law - Relationship between voltage, current and resistance. Ohm's law states that current in a resistance varies in direct proportion to voltage applied and inversely proportional to resistance.

Ohms per volt - Refers to a value of ohms per volt of full scale defection for a moving coil meter movement. The number of ohms per volt is the reciprocal of the amount of current required to produce full scale deflection of the needle. A meter requiring 50 microamps for full scale deflection has an internal resistance of 20 kW per volt. The higher the ohms per volt rating, the more sensitive the meter.

one-shot - Monostable multivibrator.

op-amp - Abbreviation for operational amplifier.

open loop gain - Gain of an amplifier when no feedback is present.

open loop mode - An amplifier circuit having no means of comparing the output with the input. (No feedback.)

operational amplifier - A high gain DC amplifier that has a high input impedance and a low output impedance. Op-amps are the most basic type of linear integrated circuits.

oscillate - To produce a continuous output waveform without an input signal present.

oscillator - An electronic circuit that produces a continuous output waveform with only DC applied.

oscilloscope - An instrument used to display a signal graphically. Shows signal amplitude, period and wave shape in addition to any DC voltage present. A multiple trace oscilloscope can show two or more waveforms at the same time for phase comparison and timing measurements.

out of phase - When the maximum and minimum points of two or more waveshapes do not occur at the same time.

output - Terminal at which a component, circuit or piece of equipment delivers current, voltage or power.

output impedance - Impedance measured across the output terminals of a device without a load connected.

output power - Amount of power a component, circuit or system can deliver to a load.

overload - Condition that occurs when the load is greater than the system was designed to handle. (Load resistance too small, load current too high.) Overload results in waveform distortion and/or overheating.

overload protection - Protective device such as a fuse or circuit breaker that automatically disconnects a load when current exceeds a predetermined value.

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