It is common to use a potentiometer to vary the electrical resistance at a particular point in an electric circuit over a range determined by the potentiometer. It is common knowledge that potentiometers are made from an electrically resistive material generally having a connection point at each end thus providing a fixed electrical resistance between the two ends. A "wiper" which is slidably movable between the two ends and also includes a connection point provides a selectively variable resistance ranging from approximately zero to the full resistance of the potentiometer. Potentiometers are generally designated by their maximum electrical resistance, such as 1K, 5K, 10K, 100K ohms, etc. Potentiometers are further designated by tolerance ranges such as .+-.20%, .+-.10%, .+-.5% or .+-.1%. It is obviously less expensive to produce a potentiometer having a .+-.20% tolerance than to produce a potentiometer having a .+-.5% tolerance. It is also common for the linearity of the resistance to vary over the length of the resistive material used in the potentiometer such that equal movements of the wiper do not always produce equal changes in resistance. Each potentiometer, regardless of its manufacturing technique, stated tolerance and quality control, has individual characteristics with respect to its maximum electrical resistance, linearity and with respect to the arc or length of travel of the wiper between its maximum and minimum resistance. In many applications the potentiometer is used to provide a variable electrical resistance that is critical to the proper operation of the electrical circuit in which it is installed. The potentiometer is generally provided with a pointer or indicator which provides an indication of the relative position of the wiper with respect to the resistive material of the potentiometer. The indicator interfaces with an indicia in the form of numbers, letters or graduation marks on a plate in fixed relationship with the potentiometer. This interface provides a relative indication of the electrical resistance at the wiper connection and thereby the resistance of the potentiometer. It is generally understood that varying the potentiometer resistance changes the output or function of the circuit in which it is installed. Therefore, in situations where the electrical resistance of the potentiometer is critical to the performance of the circuit, the interface relationship between the indicator and the indicia must accurately indicate the true electrical resistance of the potentiometer or the true circuit function. This can require further calibration of the potentiometer. Calibration is generally accomplished by adding a fixed value resistor, a laser trimmable resistor, a manually adjustable trimmer resistor or other form of selectively variable resistance in series with the potentiometer. The trimmer resistor is then manually adjusted such that the potentiometer resistance is calibrated to the desired value with respect to the interface between the indicator and indicia. However, a trimming resistor can only adjust the potentiometer value at one point and can not adjust for nonlinearity of the resistive material. These calibration methods generally require access to the printed circuit board on which the fixed resistor or trimmer resistor are attached after the device is fully assembled or at least after the indicia is in its final relationship with the potentiometer indicator. These methods of calibration also add both material and labor cost to the device being manufactured. It is therefore desirable to provide a fast, accurate and inexpensive method of calibrating each individual potentiometer with respect to its associated indicator and indicia without adding any additional electrical components to the electrical circuit or requiring access to the circuit boards enclosed within the device after assembly has been completed. It would also be desirable to calibrate a low cost potentiometer having a tolerance of .+-.20% for use in situations where a more expensive potentiometer having a tolerance of .+-.5% or less is required, or to correct nonlinearity of the resistive material throughout the potentiometer resistance range. It would also be desirable to calibrate potentiometer such that any number of desired circuit outputs or functions are accurately indicated by the interface between the indicator and the indicia.
USPTO Backgrounds
USPTO Backgrounds