414 Electrical Systems T E C H T I P Oscilloscope Probes The X100 probe is a good accessory to have when measuring higher voltages. Always be careful to make certain the multiplier or switch position of the probe you are using is set appro- priately. Check the menu setting for the probe multiplier as well. Oscilloscope Calibrator Most oscilloscopes have a built-in calibration source. Th is is a useful tool for checking the oscilloscope and probes to ensure that everything is in order. Th e calibrator output is commonly located next to the channel inputs on the scope. Th e most common calibration signal is a 5 V peak-to- peak square wave at a frequency of 1 kHz. Th e probes are coaxial in design and have a compensation adjustment on them. In a perfect scenario, the coaxial cable inductance is equal to its capacitance and the two cancel each other out. A probe compensation variable capacitor is built into the probe to allow you to zero out any inductance or capacitance. Connecting the probe to the calibra- tor and observing the square wave on the scope screen indicates if you need to make any adjustments to the compensation capacitor. On X1/X10 probes, the com- pensator is applied to only the X10 side of the probe, so be certain to check the switch. 21.3.9 Power Supplies Assemblies require various AC and DC voltages at diff erent levels. To bench test an assembly, you must provide it with the same type of power it receives in its usual operation. Th ere are many types of power supplies. Single- voltage DC power supplies provide one level of voltage. Variable DC power supplies can be adjusted among a range of voltage levels. AC power supplies include trans- formers and variable autotransformers. 21.3.10 Arbitrary Function Generators An arbitrary function generator (AFG) is a digital electronic device capable of generating analog and digi- tal signals. See Figure 21-26. An AFG, sometimes also called an “arb,” can generate almost any imaginable ana- log or digital signal. AFGs can be physical devices or may be circuit cards controlled by software on a USB- connected computer, Figure 21-27. Goodheart-Willcox Publisher Figure 21-26. This arbitrary function generator (AFG) has an analog output and multiple digital outputs. This AFG is completely software controlled, so there are no controls on the unit. A USB port allows the AFG to connect to a computer. Goodheart-Willcox Publisher Figure 21-27. This AFG control software provides all the controls to modify various waveform parameters of an AFG. Copyright Goodheart-Willcox Co., Inc.