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Glossary O
OHM: The unit of resistance usually shown as the symbol "R" one thousand ohms is written "k" and one million ohms is written"M". Ohms are measured with an ohm-meter and is one of the range on a multimeter, called the "ohms range".

Ohm's Law: Written as I=V/R where I is the current flowing, V is the voltage and R is the resistance.

Ohmeter: An instrument used to measure electrical resistance.

On/off Controller: A controller whose action is fully on or fully off.

Open Circuit: The lack of electrical contact in any part of the measuring circuit. An open circuit is usually characterized by rapid large jumps in displayed potential, followed by an off-scale reading.

Operational Amplifier(op-amp): One of the basic building blocks of analogue circuits - a high gain stable amplifier with a voltage gain of 100 to 100,000 or more.

Or gate: Logic gate whose output will be a 1 if any of it imputs is at 1.

Oscillator: A building block that produces an alternating waveform.

Oscilloscope: An instrument used to make voltage changes visible over time. The word oscilloscope comes from "oscillate," since oscilloscopes are often used to measure oscillating voltages.

Output: That part of a circuit where the processed signal is available.

Output Impedance: The resistance as measured on the output terminals of an instrument.

Output Noise: The RMS, peak-to-peak (as specified) ac component of a instrument's dc output in the absence of a measurand variation.