本文提供了一種基于 PLC 開關(guān)量輸入單元的轉(zhuǎn)速信號(hào)測(cè)量方法，該方法的特點(diǎn)在于測(cè)量成本低、可靠性高、測(cè)量精度和刷新時(shí)間穩(wěn)定。文中舉出了用PLC 開關(guān)量輸入單元測(cè)量頻率的成本優(yōu)勢(shì)，并討論了常見的頻率測(cè)量算法存在的問題，然后引入了一種變時(shí)間
窗多周期頻率測(cè)量算法，從而克服了常見的頻率測(cè)量算法測(cè)量精度和刷新時(shí)間不穩(wěn)定的缺點(diǎn)。針對(duì)轉(zhuǎn)速信號(hào)測(cè)量的硬件，分析了PLC 自身特點(diǎn)對(duì)頻率測(cè)量的影響，以及如何解決。最后給出了算法的程序流程。
關(guān)鍵字：PLC；開關(guān)量輸入；頻率測(cè)量；時(shí)間窗
Abstract: This paper presents a approach measuring the rotate speed with digital IO input unit
of PLC. This method characters high reliability, low cost and stable precision and fresh time. It
illustrates the advantage of this method in low cost, discusses some common technique to measure frequency and recommends a arithmetic of MVTW ( multicycle and vary timing window ) that implements the stable precision and fresh time. As the hardware of measurement, It discusses the influences on measuring frequency from the feature of PLC, and how to deal with these influences. At last, It provides the flow of the approach.
Keywords: PLC; input IO unit; frequency measurement; timing window