Rico

2.2  Measuring Voltage

Voltage can be measured using several different instruments depending on the application.

Multimeter

A multimeter, such as the Fluke shown in figure 1, can measure voltage, current, resistance, and sometimes capacitance. These handheld devices use two probes and can operate in one of two connection modes: high-resistance and low-resistance.

Figure 1: The front panel of a Fluke multimeter, connected in high-resistance mode.

High-resistance connection: Each probe is connected to two points in a circuit to measure voltage, resistance, or capacitance across the circuit segment. The hot probe connects to the V or Ω port.

Low-resistance connection: To measure current through the multimeter, the circuit must be broken and the multimeter inserted inline. The hot probe connects to the A, mA, or μA port.

The dial selects the measurement mode. The multimeter shown is in DC voltage measurement mode.

Going clockwise from the bottom-left of the dial (assuming high-resistance connection unless otherwise noted), the modes are:

  1. AC voltage
  2. DC voltage
  3. DC voltage—small signal
  4. Resistance
  5. Diode test
  6. Current (low-resistance)
  7. Small current (low-resistance)

Oscilloscope

An oscilloscope measures and displays voltage over time. It allows us to "zoom in" on a time window, and when properly triggered, the signal appears stationary—typically when the window matches a multiple of the signal’s period.

We are using the Tektronix DPO 2012B oscilloscope (user manual), shown in figure 2.

Figure 2: The front panel of the Tektronix DPO 2012B oscilloscope.

It features two inputs (1 and 2) and includes advanced functionality such as:

  • Cursors for measuring waveform properties
  • Signal averaging
  • Signal math
  • Fast Fourier Transform (FFT)
  • Trace capturing

Also available is the BK Precision 2120B oscilloscope (user manual), shown in figure 3.

Figure 3: The front panel of the BK Precision 2120B oscilloscope.

This older oscilloscope features two channels (CH1 and CH2). It lacks modern tools like cursors and trace capture, but retains the essential functionality for learning oscilloscope operation.