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Is that measurement correct?

The importance of using tools correctly

These days I often find myself reflecting on just what a unique task circuit design is.

Controlling an invisible world.

The foremost reason that I find circuit design special is that the designer is required to design invisible phenomena, reliant on tools. Designers attempt to represent these invisible phenomena by including information on target functions and properties in schematics and programs, but ultimately you cannot tell whether these targets have been met simply by looking at the circuit. This is why we need to use measuring equipment and other tools.

Thinking back to when I first joined Kikusui, I remember just thinking how cool my coworkers’ test bench looked, covered in measuring equipment. Watching the team effortlessly switch between multiple measuring devices as they worked was like watching a pilot in the cockpit, checking instruments and flicking switches.

Before I had much hands-on design experience, I used to place complete faith in my instruments, blindly believing that when I probed a circuit, I would always get the correct reading. I know that many circuit designers can use oscilloscopes almost as if they are an extension of their own bodies to visualize waveforms. While I realize that an experienced engineer will always make sure that the probe has been correctly calibrated before using an oscilloscope, newbie engineers are prone to skip this step and start taking measurements right away. Early in my career I encountered much strife when I attempted to measure waveforms using an uncalibrated probe.

Calibrate the probe first.

There is a lot of information available explaining why oscilloscope probes need to be calibrated and the circuits that are used in probes, so I will not go into detail here. In any case, it should be evident to the reader that you will not receive a correct result if you measure a waveform with an uncalibrated probe (Figure 1).

Figure 1. Probe Calibration

The same is true of the digital multimeters often used in circuit design. While there is no multimeter equivalent of probe calibration, you must make sure that your multimeter is capable of correctly measuring the signal in question before embarking on measurement. If you skip this step, you might get an incorrect measurement, destroy your multimeter, or, heaven forbid, get electrocuted.

While I have named this article, "Is your measurement correct", the long version might be, "can you correctly measure the signal you are trying to measure with that set up (device being measured / measurement tool)".

Measurement tools are indispensable for circuit designers. Take this opportunity to review the specifications and method of use of your measurement tools to make sure that you get the full benefit of their functions and capabilities.

TEXT BY
Misao Nojiri
Solutions Development Department

[Major achievements in product development]
Electromagnetic compatibility testing system for automotive devices
Magnetic field test system
High-Voltage superposition ripple tester
R10 testing system

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