Digital Electronics: Principles, Devices and Applications

678 Digital ElectronicsProbe BodyOscilloscope9MCCable1M10 to 50pFFigure 16.19Internal circuit of 10X probe.(a) (b) (c)Figure 16.20Probe compensation.CAL signal will appear in perfect rectangular shape [Fig. 16.20(a)] with no rounding-off of edges [Fig.16.20(b)] or any spikes on fast transitions [Fig. 16.20(c)]. Rounding-off of edges indicates too littlea probe capacitance, while spikes indicate too large a probe capacitance. The probe capacitance canbe adjusted by turning a screw or rotating the probe barrel after loosening the locking nut (in someprobes) to get a perfect calibration signal.16.14 Frequency CounterThe most basic function of a frequency counter is the measurement of an unknown frequency.Modern frequency counters, however, offer much more than just frequency measurement. Other relatedparameters such as the time period, which is the reciprocal of frequency, the time interval betweentwo events and the totalize count, which is nothing but the cumulative count over a known period, areother functions that are available with present-day frequency counters. These instruments, offering avariety of measurement options, are usually referred to as universal counters.