Sunday, March 31, 2013

Multimeter Basics: Measuring Resistance and DC Voltage

A multimeter is a great tool to have around, and even the cheapest model will offer some useful features. I mainly use my multimeter to do two things: measure resistance and measure DC voltage.

The multimeter is usually split up into different types of measurements, thus divided into quadrants of a circle. Each quadrant is then subdivided into different ranges of a particular measurement.

Connect the red probe to the VΩmA connection the multimeter. Connect the black probe to the ground com connection of the multimeter.

To measure voltage, set the multimeter to a range found within the V DC quadrant. The value selected (200mV, 2000mV, 20V, 200V 1000V) represents the maximum voltage in DC that the multimeter can read if a particular range is selected.

For example, if we are measuring the voltage across the terminals of a 9V battery, then the suitable range is 20V, as 9V is above 2000mV but below 200V (the two ranges either side).

Connect the red probe the the positive point on the circuit that is to be measured. Connect the black probe to the negative point on the circuit is to measured.

In a similar way, we can measure the resistance of a resistor or a part of a circuit. Simply select a suitable range and measure by placing the probes to either leg of a resistor.

If you have no idea what value the resistor is, or that particular part of the circuit is, then start with the lowest range (200Ω) and work up from there.

If the multimeter reads just "1" on the left hand side of the display, then the reading is above whatever range is selected. Simply move up to the next range, e.g. 2000Ω.

The results of the measurement will be in whatever unit is defined by the currently selected range. For example if the range is set to 200Ω, then the reading will be in ohms. If the range is set to 20kΩ, then the reading will be in kilo ohms.