Unleashing precision measurements with Fluke

Circuits and equipment are designed to operate at specific frequencies, and deviations from these frequencies can lead to abnormal performance.

For instance, an AC motor designed for 60 Hz will operate slower if the frequency is below 60 Hz and faster if it exceeds 60 Hz. Such frequency changes cause proportional changes in motor speed.

Digital multimeters come equipped with various modes to measure frequency:

• Frequency Counter Mode: Measures the frequency of AC signals, useful for troubleshooting electrical and electronic equipment.
• MIN MAX Recording Mode: Records frequency measurements over time, offering similar functionality for voltage, current, and resistance.
• Autorange Mode: Automatically selects the frequency measurement range. If the measured frequency is outside this range, the multimeter cannot display an accurate measurement. Refer to the user’s manual for specific frequency measurement ranges.

Using digital multimeters with a frequency symbol on the dial

• Turn the dial to Hz.
• The Hz function usually shares a spot with another function.
• Some meters access frequency through a secondary function by pressing a button and setting the rotary switch to AC or DC.
• Insert the black test lead into the COM jack.
• Insert the red test lead into the V Ω jack.
• Remove the leads in reverse order when finished: red first, then black.
• Connect the black test lead first, then the red test lead.
• Remove the leads in reverse order when finished: red first, then black.
• Read the measurement on the display.
• The abbreviation Hz should appear to the right of the reading.

Using digital multimeters with a frequency button

• Turn the dial to AC voltage (AC Voltage indicator). If the circuit voltage is unknown, set the range to the highest setting.
• Most multimeters start in Autorange mode, selecting the measurement range based on the voltage present.
• Insert the black test lead into the COM jack.
• Insert the red lead into the V Ω jack.
• Connect the test leads to the circuit.
• The position of the leads is arbitrary.
• Remove the leads in reverse order when finished: red first, then black.
• Read the voltage measurement on the display.
• With the multimeter still connected to the circuit, press the Hz button.
• Read the frequency measurement on the display.
• The Hz symbol should appear to the right of the measurement.

Frequency measurement considerations

Certain circuits may have enough distortion to prevent accurate frequency measurement. For example, AC variable-frequency drives (VFDs) can cause frequency distortions. When testing VFDs, use the low-pass filter AC V setting for accurate readings. If the meter lacks an AC voltage indicator setting, turn the dial to DC voltage and press the Hz button to measure frequency on the DC voltage setting. Adjust the voltage range to compensate for noise if the meter supports decoupled frequency measurement.