3.4 The Ohmmeter

This is the fourth and final week of Module 3 of the Navy Basic Electricity and Electronics series, which is on resistance. The three posts so far are:

• 3.1 What is resistance?
• 3.2 Resistors
• 3.3 Resistor identification

1. So an ammeter measures current (amps). A voltmeter in a sense measures the force of the current (volts). An ohmmeter measures the resistance of some circuit component (in ohms).

Of course usually these measurement functions are combined on a "multimeter," a device that can measure all of these. There are often "ranges" to these devices. So one might measure resistance in units of 1. Another setting might measure in units of 100 ohms. Another might have units of 10,000 ohms.

"It is best to use a meter range which causes the pointer to rest over the center two-thirds of the scale" (86-87). I imagine they're all digital today. :-)

2. Some miscellaneous elements of this section:

• Don't connect an ohmmeter to an energized circuit.
• The ohmmeter needs to be "zeroed" each time you change the range.
• You touch the leads together and turn on the "zero ohms" control to zero it.
• Turn the range switch to the 1000 volt scale when you are done to save the battery.
• An ohmmeter can help you find the point where a circuit is disconnected (an open circuit). At that point it will read infinity.