CHAPTER 5 ■ NUMBERS AND UNITSTable 5-2. Units Common in Robotics
Measurement Units Abbreviation Usually Refers To
length or distance meter m component dimensions, material thickness
resistance ohm W resistors, motor coils
voltage volt V batteries, motors, chips
current ampere or amp A circuits, power supplies, motors
power watt W circuits, motors
frequency hertz Hz crystals, chips, signals
capacitance farad F capacitors
inductance henry H inductors
amplification beta factor hFE or b transistors
luminous intensity candela cd LEDs
mass gram g motors, batteries
torque newton-meter Nm motors
capacity amp-hour Ah batteries
temperature Celsius °C chips, sensors, solder
rotational speed revolution per minute rpm motors
Abbreviating Units
Besides abbreviations for multipliers, there are also abbreviations for the units or types of measurements:
Frequently, the multiplier (see Table 5-1) is combined with the units (see Table 5-2). For example, older
personal computer processors are rated in MHz (megahertz). The M part represents millions (see Table 5-1),
the Hz parts represents hertz (see Table 5-2).
Another ordinary example is millimeters, abbreviated mm. The first m represents thousandths; the
second m represents meters. So, a millimeter is one-thousandth of a meter, or 0.001 meter.
Too Little
On most parts, the values and units are printed directly on the case (see Figure 5-4). For example, on a large
motor, you might see “24-volt DC permanent magnet reversible motor, 0.5 amp no load, 8-ohm coil, Part
#54321, manufactured December 6, 2001 by McCloskey and Son Corporation, Visit our Web site! Say, that
reminds us of a funny story...”