Sunday, April 24, 2016

Signal probing using handheld multimeter or handheld oscilloscope


Signal probing requires some understanding on the circuitry to determine the signal test point and to interpret the result. Signal probing can be done with a voltage test using a handheld multimeter or a waveform capture with an oscilloscope. Most voltage tests start by probing the voltage with reference to the ground. When checking an integrated circuit (IC), it normally starts with testing the voltage supply pin. If the voltage level is lower than expected, there could be leakage on the IC.

Sometimes, instead of depending on a measurement value displayed on the handheld multimeter, the engineers or technicians will need more information of the signal by monitoring the waveform pattern to determine the possible cause of failure. Oscilloscopes will be useful in this situation. The oscilloscope is used to monitor and display the signal in a graphical format. The oscilloscope shows how the signal changes, allowing the engineers and technicians to detect any anomalies easily.


Occasionally, engineers or technicians will need to make floating measurement in which the measurement point is not referenced to the earth ground. Most benchtop oscilloscope measurements are referenced to the earth ground as the signal ground terminal is connected to the protective earth ground system. The Keysight U1610A/U1620A handheld oscilloscope offers channel-to-channel isolation to enable the capture of two signals at different reference points.
Figure 5 Two different floating measurement waveforms captured using Keysight U1620A handheld oscilloscope with channel-to-channel isolation (left) and Keysight U1604A handheld oscilloscope without channel-to-channel isolation (right)



The Keysight U1610A 100 MHz handheld oscilloscope and U1620A 200 MHz handheld oscilloscope with VGA display allow us to clearly see and differentiate signals from both channels simultaneously similar to working on a benchtop oscilloscope. The scope isolation channels enable floating measurement capability. With up to 2 GSa/s sampling rate and 2 Mpts memory depth, the U1610A/U1620A captures more waveforms from signals and the zoom-in function allows for a more detailed view.

Comparing the circuit boards

To determine the root cause of a defective circuit board quickly, technicians will usually compare the test value of a defective circuit board with a known good circuit board. This is done by probing the circuit board’s reference points with a digital multimeter and comparing the values between the defective circuit board and a known good circuit board.

The Keysight U1200 series handheld digital multimeters with up to 4 ½ digit display resolution deliver the precision, accuracy and repeatability that the technician needs during troubleshooting. Coupled with the U1163A SMT grabbers and the U1164A fine tip test probes, physically small connections to the device under test (DUT) such as the SMT component can be achieved.

Intermittent failure


Intermittent failure is the most challenging part to address in the troubleshooting process. It can be very time consuming. There are many factors which result in intermittent failures. The common faults are component overheat, poor soldering and components degradation. Intermittent failure can be attended by monitoring the voltage value of the suspected component with a handheld multimeter or an oscilloscope over time to determine if there are any changes to the signal.
Figure 6 Monitoring the voltage value over time with the data logging capability using the Keysight Handheld Meter Logger Software

Summary

The choice of the troubleshooting method depends on the complexity of the circuitry, the knowledge and experience of the person who performs the troubleshooting task. The use of relevant test tools will help the engineers and technicians to identify the cause of failure quickly and accurately; subsequently increase the work productivity.

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