Function generator

DETAILED DESCRIPTION The present invention relates to a function generator for generating inverse time characteristics for, for example, time-lag-type over-current relays by approximating the time function by means of individual straight parts which are put together to a time function being discontinuous in a number of break points.
Besides the integrating circuit, which will not be further described, the function generator comprises an operational amplifier with at least one input and one output and a number of amplifier circuits, known per se and corresponding to the number of break points in the approximated time function, said amplifier circuits having at least one input and one output and each one operating as a diode with ideal characteristics.
According to the invention, the input of each of the amplifier circuits is connected to an input voltage source.
An arrangement is provided for selectively connecting the output of each of the amplifier circuits to the input or output of the operational amplifier, depending on whether the linear part of the time function, determined by a selected amplifier circuit, has a greater or smaller derivative than the preceding linear part of the time function.
By using ideal diodes, that is diode connections which in their function are both current and temperature-independent, for generating the individual curve parts, the function generator will become temperature-and current-independent.
An alteration in the derivative of the approximated time function in various areas of the function can be easily obtained by changing the connections of the amplifier circuits used to the operational amplifier.