Abstract: A filter system is provided to remove electrical supply line noise at a first frequency from an input signal to a medical monitor. An arithmetic unit produces an intermediate signal having a frequency component that corresponds to a difference between the first frequency and a reference frequency. A calculator determines the period of the intermediate signal and a signal converter produces a sinusoidal signal which has the period determined by the calculator. An adder produces a filter control signal having a value that represents the sum of the reference frequency and the frequency of the intermediate signal. A notch filter is employed to remove the electrical supply line noise from the input signal. The filter control signal tunes the notch filter to the first frequency of the electrical supply line noise.

Abstract: A power supply has a transformer for isolating circuitry to which power is furnished from the electrical supply lines. The transformer includes a core of ferro-magnetic material with primary and secondary windings wound side-by-side on the core. The primary winding has two layers of turns with a center tap formed at a connection of the turns of each layer that are closest to the secondary winding. Similarly, the secondary winding has two layers of turns with a center tap formed at a connection of the turns of each layer which are closest to the primary winding. A driver applies excitation voltage across the center tap, which also is coupled to earth ground, and a turn of the innermost primary winding layer. The center tap of the secondary winding is used as an isolated ground and a supply voltage is produced between two turns from different layers of the secondary winding.

Abstract: A medical monitor determines the period of a physiological function, such as blood circulation pulses, by operating a probe that produces an electrical signal which corresponds to the physiological function. The electrical signal is digitized at a given sampling rate to acquire a plurality of signal samples which are stored in a memory. A time scaling factor is adjusted dynamically so that the amount of signal samples being processed does not exceed a maximum limit. The magnitude of the signal samples also may be scaled dynamically. Serial autocorrelation is applied to the signal samples to produce a sequence of summation values. The quantity of summation values from the initial one in the sequence to a peak summation value is determined. The physiological function period is derived from the quantity of summation values, the given sampling rate, and any time scaling factor that was used.