Kel ProRata

ProRata is the core technology at Kel and a primary building block for a multitude of instrumentation

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About The Specifications

ProRata has its roots in an old latin term that means proportional rate. Consumers most often come across it when they exercise a guarantee on a tire. The guarantee is pro-rated that means if the tire cost $100 and it's guaranteed for 50,000 miles, if it wears out at 25,000 miles, the pro-rated charge for replacement is $50. The term "proportional" fits well into this description because the pro-rated amount that will be paid to replace the tires is based on, and in proportion to, how much of the tires were used, in this case 50% before they needed replacement.

Electronic pro-rata is proportional rate in units such as volts, feet, gallons, miles, degrees, etc. The scale is a linear span or measurement range. As an example, if the span is measured from 0 to 5 (miles) it can be represented electrically, in "proportion", by 0 to 5 volts.

Rate comes from calculus, that dreaded area of math that causes so many students to regularly cut class. Rate is differential calculus that produces a derivative, a value composed of the mathematical mix, or combination, of linear change, and time. Some examples of rate would be degrees per hour, gallons per minute, feet per second, millivolts per hour, or the one most regularly observed when driving, miles per hour as displayed on the vehicle speedometer.

A speedometer displays "instantaneous" rate of change, which means that it is continously changing, in infinitely small amounts, or increments. Airplane pilots fly with an instantaneous rate instrument called "rate of climb" that displays in "feet per minute" how rapidly the aircraft is climbing or descending. The rate of climb indicator came into existance in the early days of aviation to anticipate and display very small changes in altitude before it could be visually detected on the altimeter. From that came the use of the term "anticipation", or anticipative. If it was possible for the altimeter to indicate small increments of altitude, the pilot could make corrections sooner. The rate of climb indicator displays feet per minute of change in altitude to provide the necessary "anticipation" or instantaneous rate of change.

ProRata recieves the electrical signal voltage from a sensor, or other electrical source, and produces a very accurate, high resolution, instantaneous rate derivative. For most applications the rate signal is generated on a linear scale from 0 to 5 volts DC. Other scales such as 0 to 10 volts DC, or plus/minus voltages are also available.

A good example of ProRata in a sensor application is the weather station barometer that's used for sensing atmospheric pressure in millibars. The barometric pressure sensor provides an electrical output scale of 0 to 5 volts DC that is in proportion to the atmospheric pressure range of the sensor, 800 to 1100 millibars (28 to 32 inches of mercury). Normally the sensor will output a single linear span pressure signal. When ProRata is connected, a "secondary", instantaneous rate signal is generated that can be scaled down to levels as low as one tenth (.1) of a millibar per hour (.01 inch of mercury). A valuable aviation and public safety application is being researched. The Kel meteorological sciences division, Precision Atmospheric Instrumentation (PAI), is using PROrata electronics as an enhancement to its Scenario Weather Station barometer for anticipating the buildup of severe thunderstorm cells at long distances.

ProRata is available as an embedded component in selected models of TSM digital meters, and is also produced in a 24 pin DIP package.

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