A measurement averaging counting apparatus employing a randomly phase modulated time base provides resolution improvement when measuring an applied signal comprising time intervals or pulsed frequencies repetitively occurring at rates synchronous to a counter's clock frequency. The phase of a reference frequency is varied in response to a random signal. The phase modulated reference frequency is applied to a frequency multiplier chain which multiplies both the frequency and the effective amount of phase modulation. The randomly phase shifting output of the frequency multiplier chain is applied as a clock signal to a measurement averaging counter thereby destroying coherence between the clock signal and the applied signal and allowing statistical averaging to take place.
A method and apparatus for the measuring of a delay in a delay circuit by making a continuous frequency measurement is proposed. The phase-locking of a variable frequency signal applied to the delay circuit allows the user to significantly improve the precision and accuracy of the time delay measurement. A scheme to extract the number of cycles stored in the delay circuit is also disclosed.
In a method for converting input analog signals to time signals and the time signals thus obtained to digital values, an arbitrary value is preset in a scaler as an offset prior to effecting a conversion and counting and the conversion and counting is effected by the time signals. A value the same as the preset value is digitally added, after the conversion and counting, to a counter in a direction in that the preset value is cancelled. The differential non-linearity is actually improved by varying the preset value every conversion and counting.
A regularly repetitive, almost periodic but non-regularly shaped waveform is amplitude sampled at an interval different from that of the waveform under investigation. For a voltage measurement, the positive samples are averaged for a predetermined count number (one set) and the negative samples are likewise averaged. Zero value samples are ignored. The highest absolute value of the two is taken as a meaningful measurement. Alternatively, one of these values can be selected. For a current measurement, a running average for a predetermined number of sets can also be developed. Finally, frequency can be developed by sensing the transitions and operating a counter on/off at the beginning and ending of a waveform cycle. The count of regular interval counts is then multiplied by the interval time to give the period of the waveform. The reciprocal of the period is a measure of the frequency.
A printer having greatly reduced radio frequency interference from the system clock signal therein is provided by angle modulating the system clock signal in accordance with a desired modulation signal. The modulation signal is chosen so as to spread and thereby reduce the energy level of the system clock signal at the carrier and at the harmonics without interfering with proper detection of the system clock signal by the electronic circuits within the printer requiring the clock signal for proper timing. In a first embodiment the angle modulation is provided by an FM modulator responsive to a modulating signal which is either sinusoidal or randomly varying in nature. In a second embodiment the angle modulation is provided by an arrangement which combines a modulated subcarrier with the basic clock frequency in a phase locked loop.
Apparatus for adjusting the key activating force or "touch" for a keyboard or for one or more function key groups on that keyboard to the needs of any individual operator.
