How to measure frequency and duty cycle with a multimeter?
What is frequency?
The frequency indicates how fast the signal moves. Take a sinusoidal signal. The power plant sends out a waveform. So we take this signal and transmit it down. The frequency in the United States is 60 Hertz, which means 60 cycles in one second. The EU European Union is 50 Hz, and if you're working with aerospace systems, they're at 400 Hz, which shows how fast the signal travels, and when you're dealing more with drive motors, this measurement gets a little more complicated because The drive motor will pulse width modulate the normal sinusoidal signal to output the PWM signal. An ordinary multimeter will not be able to measure the frequency of this signal correctly. We have a Low-Pass low-pass filter key on the Fluke 87V, which will accurately Measure the frequency of this PWM signal so you can check if the motor is actually at 60 Hz or 30 Hz at 1/2 speed, or 15 Hz at 1/4 speed.
What is duty cycle?
The duty cycle is the ratio of the high level to the low level period, which can help you diagnose power quality problems. If it is a good periodic signal, then the positive and negative should be average and symmetrical. If it is A bad quality signal with lots of harmonics, we'll see only 20%-30% positive, and 80% negative after 20% positive, so with a simple duty cycle test, We can judge whether the waveform is symmetrical or not. Fluke 87V also has the function of measuring duty cycle.
The Method of Measuring Frequency and Duty Cycle with Digital Multimeter
A) Turn the function/range selection switch to the Hz position, as shown in the figure.
B) Insert the red and black test leads into the VΩHz and COM input terminals respectively.
C) Connect the test end of the test lead to the signal source to be tested in parallel.
D) When performing frequency measurement, press the Hz/DUTY key once to enter the duty ratio measurement state, and press the Hz/DUTY key again to return to the frequency measurement state.
E) When measuring current or voltage, press the Hz/DUTY key once to enter the frequency measurement state, press the Hz/DUTY key again to enter the duty ratio measurement state, and press the Hz/DUTY key for the third time to return to the original measurement state.
F) Read the current measurement result from the display.
