Date: 9th March 2015
Revision: 1st


The APM Frequency meter can measure Frequencies between 30Hz and 400Hz

The APM-FREQ meter can detect frequency in two ways:


1.  Zero Crossing Points

2. Upper and lower Threshold levels


The following sections discuss each configuration in more detail.



Zero Crossing Points

Using the free APM configurator software the APM-FREQ can be set to measure the period between zero crossing points as in the case of an AC waveform.



Upper and Lower Threshold Levels

Or to measure the period between an upper and lower offset threshold as in the case of a DC waveform




The threshold upper and lower voltages can be set in the software



The Frequency of the applied waveform is calculated as:application-note-frequency-4


This calculation is carried out over a 30mS sample period and an average is calculated. Therefore any noise or runt pulses will lead to inaccurate display


The input impedance of the APM-FREQ is approximately 1.5MΩ