Vol. 107, Issue 8, August 2009, pp.1-16

Precise Frequency and Period Measurements for Slow Slew Rate Signals
Based on the Modified Method of the Dependent Count

Sergey Y. Yurish

International Frequency Sensor Association (IFSA),

C/Llorens Artigas, 4-6, planta 0, Edifici U, Campus Sud, 08028 Barcelona, Spain

Tel: +34 696067716, fax: +34 93 4011989

E-mail: SYurish@sensorsportal.com

Received: 1 July 2009   /Accepted: 15 August 2009   /Published: 25 August 2009

Abstract: This paper describes an application of novel modified method of the dependent count for measuring the frequency (period) of slow slew rate signals (common for the conversion-to-digital of resistance, capacitance, inductance or resistive-sensor–bridge signals based on direct connection to a microcontroller). The AVR 8-bit ATmega168-20PI microcontroller (Atmel), based on advanced reduced instruction set computing architecture, was used. The modified method of the dependent count improves the accuracy of period measurements for the slow slew rate signals of triangular, sine, exponential rise and fall, as well as rectangular waveforms, by 2-to-3 orders in comparison with the accuracy achieved with classical indirect counting in all frequency ranges. The error is evaluated from the statistical characteristics and histograms of measured pulse periods, quantitatively confirming the advantages of the modified method for frequency (period) measurements for non-square pulse signals. Measurements are further improved (becoming about 1.5 times more accurate) for some waveforms when an external Schmitt trigger is used.

Keywords: Period measurement; Modified method of the dependent count; Frequency measurement

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