如何从波形图中读取波形的频率等

kira

想要从一个设备读取产生的波形，然后在labview有什么控件可以读出该波形频率，上下限等。谢谢，还有各位高手有没有好的labview基础知识的电子图书介绍呢。谢谢~~

petty88

在信号处理的工具中就有控制可以直接读出波形的频率及幅度.

cpubbs

http://www.cpubbs.com/bbs/viewth ... &extra=page%3D1

这里有较多基础知识的内容！

kira

谢谢各位。还有想请教一个问题Get Waveform Attribute中 vlaues 返回有几个值阿，分别代表什么阿？谢谢~~

cpubbs

兄弟您可以用鼠标对着它的输出的线，然后LV的帮助助手会显示出来它的数据的形式，以及它里面有些什么样的一些元素的！

kira

我按着你的方法做了，可是没有显示出来，不知道我什么地方搞错了。还有我用的是labview6i的，用什么快捷键可以显示帮助助手（Ctrl+H）吗？

cpubbs

早期的好像不太记得有没有，在LV的右上角有一个问号，点击就能打开的！

kira

我用labview8.2的试用版打开了帮助，可是好像没有您说显示它的数据类型与个数，那还有没有其它的方法呢，急着用，谢谢~~

lgh269

帮助专门做了详细说明
附图是鼠标放在连接线上帮助显示

Get Waveform Attribute Details
This function has two modes of behavior depending on whether you wire the name parameter. By default, the function returns the names of all attributes and their corresponding values in 1D arrays. If you wire name, the names output changes to a Boolean output found, the values output changes to a variant output value, and the function searches for only the specified attribute. If the function does not find the specified attribute(s), or if it cannot convert the attribute(s) to the default value, found is FALSE, and value displays the contents of default value.

The following table lists the waveform attributes set by NI-DAQ.

Name Attribute Data Type Acceptable Values Description
Hardware Device Number NI_DeviceNumber String Any value is acceptable for NI_DeviceNumber. NI_DeviceNumber is the device number of the hardware device producing the waveform.
Name of Channel NI_ChannelName String Any value is acceptable for NI_ChannelName. NI_ChannelName is the name of the virtual channel producing the waveform.
Unit for Data NI_UnitDescription String Volts, PSI, and so forth are acceptable values for NI_UnitDescription. NI_UnitDescription is the units of measure for the waveform.

The following table lists the waveform attributes set by Express VIs.

Name Attribute Data Type Acceptable Values Description
Start Timestamp NI_ExpStartTimeStamp Time stamp Any value is acceptable for NI_ExpStartTimeStamp. NI_ExpStartTimeStamp is the time stamp of the first sample in the first waveform. In Express VIs, this is set once per start of the VI and does not change, even if waveform data is generated in a loop. In Express VIs, NI_ExpStartTimeStamp is set according to the PC clock unless the waveform originates in NI-DAQ. When the waveform originates in NI-DAQ, NI-DAQ sets NI_ExpStartTimeStamp.
Timestamp NI_ExpTimeStamp Time stamp Any value is acceptable for NI_ExpTimeStamp. NI_ExpTimeStamp is the time stamp of the first sample in the waveform. In Express VIs, NI_ExpTimeStamp is set according to the PC clock unless the waveform originates in NI-DAQ. When the waveform originates in NI-DAQ, NI-DAQ sets NI_ExpTimeStamp.
X Dimension NI_ExpXDimension String Use a single character for the NI_ExpXDimension value. Currently, only t for time and f for frequency are supported. The value for NI_ExpXDimension is case sensitive. If the value of NI_ExpXDimension is t, t0 and dt are unchanged. If the value of NI_ExpXDimension is f, Express VIs interpret t0 and dt as f0 and df. For all other values, or unknown dimension, t0 and dt are interpreted as X0 and dX.
Relative Time? NI_ExpIsRelativeTime Boolean TRUE or FALSE are acceptable values for NI_ExpIsRelativeTime. If and only if NI_ExpXDimension is t, Express VIs set t0 as a relative/absolute time stamp value.
Note  Express VIs also use the attributes set by NI-DAQ. If the waveform does not originate in NI-DAQ, Express VIs add NI_ChannelName.

[ 本帖最后由 lgh269 于 2008-2-1 12:04 编辑 ]

kira

我想读取波形的属性，然后显示出来，我把它保存在一个variant的数组中，可是在前面板中没有都没有阿？不知道那步出错

lesec

在express裡面信號分析裡有tone measures函數可以讀出