In the development or debugging of circuits or electrical wiring, there can come a time when neither logic probe nor multimeter (nor oscilloscope for that matter) will display a signal. The reason is because nothing is connected to the input of the device or circuit under test, or because the circuit connected upstream is not outputting a signal. This is where a digital pulser is needed.
The pulser is simple instrument. It has a probe body equipped with a needle-point electrode. When touched to a conductor, circuit node or device terminal, it injects a single pulse or pulse train which can be seen at the output (if it is present) by the logic probe, multimeter or oscilloscope. So we see that while the pulser is used somewhat less frequently than the logic probe, it is nevertheless quite essential when an input is needed.
Another instrument that is highly relevant to digital debugging and troubleshooting is the digital current tracer. Here again the tool’s appearance resembles that of the logic probe. But its functionality and physical construction are quite different. The digital current tracer has a probe-body construction but rather than a needle-like electrode, it has a magnetic pick-up head.
The basic idea is that the tracer detects the magnetic field that surrounds a conductor or trace through which current is flowing. It does not matter if the conductor is insulated. To work properly, the current tracer must be held vertically above the conductor. Moreover, there is a dot on the tip of the current tracer that must be aligned with the current flow.
The current tracer is responsive to current over a wide range, typically from 1 mA to 1 A. A prominent indicator lamp resides at the probe tip and its brightness varies with the amount of current. A control can be used to adjust sensitivity. Then, the procedure is to move along a conductor or trace, taking note of the current. An abrupt change signals that a current sink or source has been located.
Trouble can arise when there is a fault within an IC, but such difficulties are probably less frequent than nearly-invisible solder bridges that ground out (with varying amounts of resistance) or short adjacent live traces. When this fault has been corrected, operation is frequently restored without wholesale replacement of numerous semiconducting devices.
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