示波器时基计算，采样率，采样点数，降采样点数，块与块采集间隔

1、关于示波器时间计算的分析

• 125MS /s采样率，理论1S采集125M个点
• 125/50 = 2.5MS采集工频的波形一个周期20ms，即采集一个工频完整波形返回2.5M个点
• 降采样系数（假设500），则最大或最小值的缓存数组长度 = [5000]
• 块模式一次采集2.5M个数返回5000个数，开始下一次块采集
• 块模式采集样本的数量是由参数（在触发事件之后返回的样本数 = 2.5M）决定的

由此过程设置了示波器采集的样本总数，返回的样本数，以及在工频下最大采样率采集一个周期返回的最大样本个数

 2、时基计算

•         //        This function calculates the sampling rate and maximum number of samples for a
          //given timebase under the specified conditions.The result will depend on the number of
          //channels enabled by the last call to ps5000aSetChannel.
          //This function is provided for use with programming languages that do not support the
          //float data type.The value returned in the timeIntervalNanoseconds argument is
          //restricted to integers.If your programming language supports the float type, then
          //we recommend that you use ps5000aGetTimebase2 instead.
          //To use ps5000aGetTimebase or ps5000aGetTimebase2, first estimate the
          //timebase number that you require using the information in the timebase guide.Next,
          //call one of these functions with the timebase that you have just chosen and verify that
          //the timeIntervalNanoseconds argument that the function returns is the value that
          //you require.You may need to iterate this process until you obtain the time interval
          //that you need.

 

 

在公共类CSettingPico里面定义变量

 　　　　/// <summary>
        /// 典型值50Hz
        /// </summary>
        internal float fPeriodOfSignal = 50;
        
        /// <summary>
        /// 15-bit8-bit：
        ///   Range ： 3 ~ 2^32 - 1
        ///   Sample interval formula: (timebase - 2)/125,000,000
        ///   Sample interval examples:
        ///             3 => 8ns
        ///             4 => 16ns
        ///             5 => 24ns
        ///             ...
        ///             2^32 - 1 => ~34.36s
        /// </summary>
        internal uint nTimeBase = 0;

在公共类CSettingPico里定义方法 SampRateToTimeBase()

 /// <summary>
        /// 通过参数获取 TimeBase值
        /// </summary>
        /// <param name="FACBASE">每秒最大采样数125M</param>
        /// <param name="Rate">设定每秒采样数≤125M (必须>0)</param>
        /// <param name="signalPeriod">信号周期，典型值50Hz</param>
        internal void SampRateToTimeBase(int Rate, float signalPeriod, ref int buffLen)
        {
            const int FACBASE = 125000000;
            
            if (Rate == 0 || signalPeriod == 0) return;

            //获取采样时间长 ns， 1,000,000,000ns = 1s
            //int timeLen = (int)(1000000000 / signalPeriod);

            //获取采样间隔 Rate = 每秒采集点数
            //eg. 8ns : Rate = 125,000,000, TimeBase = 3
            nTimeBase = (uint)(FACBASE / Rate) + 2;
            //1S采集（Rate = 125M）个点数，1个周期采集2.5M个样本250W，上传到电脑2500000/downSampleRatio（1000） = 2500个数据
            buffLen = (int)(Rate / signalPeriod); 
        }

在公共类CSettingPico里定义公开方法 

调用了上一步定义的方法，计算得出了数组的长度

       /// <summary>
        /// 得到存放最大值最小值数组的长度
        /// </summary>
        internal void InitSettings()
        {
            SampRateToTimeBase(this.nSampRate, this.fPeriodOfSignal, ref this.nBufferLength);
            if (this.nBufferLength > 0)
            {
                this.nBufferMax = new short[this.nBufferLength / this.downSampleRatio];
                this.nBufferMin = new short[this.nBufferLength / this.downSampleRatio];
                this.noOfPostTriggerSamples = this.nBufferLength; //在触发事件之后返回的样品个数，注意不是降采样后返回的，而是pico采集的实际样品个数
            }
        }