Meter control circuit

Claim 1

In combination with a meter movement having a pointer movable over a variable value indicating scale having numbered variable value indicating marks forming respective scale segments having substantially different compression or expansion ratios and representing progressively increasing variable values over the entire extent of said segments, a meter control circuit for feeding current to said meter movement to provide meter indications of an electrical variable which may have a value within a range from a relatively low minimum value to a relatively large maximum value as indicated by the movement of said pointer over said scale segments, said meter control circuit comprising: respective amplifier circuits for controlling the variation of pointer movement over said respective segments of said scale, each of said amplifier circuits being capable of producing an output which reaches a maximum possible output level when the signal fed to the input thereof is of a value which is to move the pointer of said meter movement to the uppermost point of the associated scale segment, said amplifier circuits including operational amplifiers each having an output terminal, a positive input terminal, a negative input terminal and positive and negative supply terminals, and a feedback resistor connected between each output terminal and a corresponding input terminal so that input current flows through said feedback resistor into the output terminal of the operational amplifier, the other input terminal of each operational amplifier being at the same reference potential, each feedback resistor being of a value so that the flow of the total increment of current to be handled by the amplifier involved results in a voltage drop which saturates the operational amplifier; means for summing the outputs of said respective amplifier circuits and feeding the same to said meter movement; an input circuit for carrying electrical current which varies over a range of values from a relatively low minimum value to a relatively large maximum value which will cause the meter movement pointer to span all of said segments of said scale; and signal directing means for respectively directing to said amplifier circuits signals resulting from the flow of respective incremental ranges of current values in said input circuit to cause said meter movement pointer to traverse said respective segments of said scale, said signal directing means including a series of similarly oriented series connected rectifiers arranged to pass the input current, the opposite terminals of said series of connected rectifiers being connected between the corresponding input terminals of the amplifiers which are to amplify successive incremental portions of the input current, each of said operational amplifier circuits maintaining said corresponding input terminal to which the feedback resistor is connected at said reference potential until the operational amplifier has become saturated, whereupon the voltage at said later input terminal will increase to enable conduction of the next increment of the input signal through the rectifier connected thereto which directs the current to the corresponding input terminal of the operational amplifier to handle the next incremental portion of the input signal.