truAPM | Advanced Panel Meters by truAPM
truAPM | Advanced Panel Meters by truAPM

Application Notes

Introduction
 
 
The APM Frequency meter can measure Frequencies between 2Hz 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