# PSID

 pounds per square inch differential.

## Related Terms

### DIRECTIVITY FACTOR

1. The ratio of radiated sound intensity at a remote point on the principal axis of a loudspeaker or other transducer, to the average intensity of the sound transmitted through a sphere passing through the remote point and concentric with the transducer; the frequency must be stated.
2. The ratio of the square of the voltage produced by sound waves arriving parallel to the principal axis of a microphone or other receiving transducer, to the mean square of the voltage that would be produced if sound waves having the same frequency and mean-square pressure were arriving simultaneously from all directions with random phase; the frequency must be stated.

### PLAN EQUATION

The mathematical statement that horsepower plan/33,000, where p mean effective pressure (pounds per square inch), l length of piston stroke (feet), a net area of piston (square inches), and n number of cycles completed per minute.

### PIE`ZE

A unit of pressure equal to 1 sthe`ne per square meter, or to 1000 pascals. Abbreviated pz.

### PICTURE ELEMENT

1. That portion, in facsimile, of the subject copy which is seen by the scanner at any instant; it can be considered a square area having dimensions equal to the width of the scanning line. 2. In television, any segment of a scanning line, the dimension of which along the line is exactly equal to the nominal line width; the area which is being explored at any instant in the scanning process. Also known as critical area; elemental area; pixel; recording spot; scanning spot.

### PERCH

Also known as pole; rod. 1. A unit of length, equal to 5.5 yards, or 16.5 feet, or 5.0292 meters. 2. A unit of area, equal to 30.25 square yards, or 272.25 square feet, or 25.29285264 square meters.

### OFFSET YIELD STRENGTH

That stress at which the strain surpasses by a specific amount (called the offset) an extension of the initial proportional portion of the stress-strain curve; usually expressed in pounds per square inch.

### NYQUIST'S THEOREM

The mean square noise voltage across a resistance in thermal equilibrium is four times the product of the resistance, Boltzmann's constant, the absolute temperature, and the frequency range within which the voltage is measured.

### MORTISING MACHINE

A machine employing an auger and a chisel to produce a square or rectangular mortise in wood.

### MISTUNING

The difference between the square of the natural frequency of vibration of a vibrating system, without the effect of damping, and the square of the frequency of an external, oscillating force.

### MERSENNE'S LAW

The fundamental frequency of a vibrating string is proportional to the square root of the tension and inversely proportional both to the length and the square root of the mass per unit length.

### Related questions

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