Date: 9th March 2015
Revision: 1st

Introduction

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.

application-note-frequency-1

 

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

 

application-note-frequency-2

Setup

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

application-note-frequency-3

 

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

 

application-note-frequency-5