CHAPTER 4 ■ DIGITAL MULTIMETER
Temperature
Measured in degrees Celsius or degrees Fahrenheit, a temperature mode indicates how hot or cold
something is. It could be useful to answer the age-old question “Does this feel like it’s getting hot to you?”
Only some multimeters have this feature.
Sound
Measured in decibels, a sound mode indicates how loud or quiet something is. It could be useful for motor,
speaker, or microphone volume testing. Few multimeters have this feature.
Count
A counter measures the number of times something occurs, regardless of length of time. Many multimeters
have this feature.
Bar Graph
Digital meters don’t react instantly to changes in measured values. Instead, they average their readings over
a short period of time and update the display only a couple of times per second (analog-nostalgic supporters
point to this weakness). So, some digital multimeters supplement their display with a bar graph, which is a
rapidly updating single-axis line (see Figure 4-12).
Figure 4-12. Digital bar graph allows DMMs to approach responsiveness of analog meters
Data Hold
Data hold prevents the screen from changing from the currently displayed value. Most meters continue
to display the current measured value but place the held value somewhere else on the screen. Many
multimeters have this feature.
Data Auto
A data-auto mode periodically moves the measured value to the smaller portion of the dual display. This
makes it clear when the ongoing value is changing, since the small and large display won’t have the same
value for a few seconds.
High/Low/Logic
A logic mode interprets the DC voltage measurement as a logical signal, indicating low, high, or an improper
value in between (see Figure 4-13). It’s better to do this in your head using the meter’s voltage mode.
Depending on the parts you choose, the robot’s chips may accept a certain voltage as “high” that the meter
may consider “low.” This is especially likely with the recent advent of low-voltage chips. Most multimeters
have this logic mode feature.