Agilent 5991-2325EN Oscilloscope Selection Tip 11 Probing - Application Note c20130724 [2] free download

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Oscilloscope Selection Tip 11: Probing Part 11 of a 12-part series Tip 11 Select an oscilloscope from a vendor that can also provide the variety of specialty probes that you may require. Your oscilloscope measurements can only be as good as what Agilent offers a broad range of your oscilloscope probe delivers to the oscilloscope's BNC inputs. oscilloscope probes to fit your When you connect any kind of specific voltage and current measurement system to your circuit, the instrument (and measurement applications. probe) becomes a part of your device-under-test. This means it can "load" or change the behavior of your signals to some degree. Good probes should not disturb the input signal and should ideally deliver an exact duplicate of the signal that was present at the probe point before the probe was attached. When you purchase a new oscilloscope, it typically comes standard with a set of high- impedance passive probes -- one probe for each input channel of the oscilloscope. These types of general-purpose passive probes are the most commonly used and enable you to measure a broad range of signals relative to ground. But these probes do have limitations. Figure 1 shows an electrical model of a typical 10:1 passive probe connected to the high-impedance input (1-M input of an oscilloscope). Figure 1: Typical model of a 10:1 passive probe Inherent in all oscilloscope probe and oscilloscope inputs are parasitic capacitances. These include the probe cable capacitance (Ccable), as well as the oscilloscope's input capacitance (Cscope). "Inherent/parasitic" simply means that these elements of the electrical model are not intentionally designed-in; but are just an unfortunate fact of life in the real world of electronics. The amount of inherent/parasitic capacitance will vary from oscilloscope-to-oscilloscope and probe-to-probe. Also included in this electrical model are designed-in capacitive elements that are used to compensate for