示波器時基計算，采樣率，采樣點數，降采樣點數，塊與塊采集間隔

1、關於示波器時間計算的分析

• 125MS /s采樣率，理論1S采集125M個點
• 125/50 = 2.5MS采集工頻的波形一個周期20ms，即采集一個工頻完整波形返回2.5M個點
• 降采樣系數（假設500），則最大或最小值的緩存數組長度 = [5000]
• 塊模式一次采集2.5M個數返回5000個數，開始下一次塊采集
• 塊模式采集樣本的數量是由參數（在觸發事件之后返回的樣本數 = 2.5M）決定的

由此過程設置了示波器采集的樣本總數，返回的樣本數，以及在工頻下最大采樣率采集一個周期返回的最大樣本個數

 

 2、時基計算

•         //        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.

 

 

 

 

 

 

在公共類CSettingPico里面定義變量

 　　　　/// <summary>
        /// 典型值50Hz
        /// </summary>
        internal float fPeriodOfSignal = 50;
        
        /// <summary>
        /// 15-bit\8-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;

 

 

在公共類CSettingPico里定義方法 SampRateToTimeBase()

 /// <summary>
        /// 通過參數獲取 TimeBase值
        /// </summary>
        /// <param name="FACBASE">每秒最大采樣數125M</param>
        /// <param name="Rate">設定每秒采樣數≤125M (必須>0)</param>
        /// <param name="signalPeriod">信號周期，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;

            //獲取采樣時間長 ns， 1,000,000,000ns = 1s
            //int timeLen = (int)(1000000000 / signalPeriod);

            //獲取采樣間隔 Rate = 每秒采集點數
            //eg. 8ns : Rate = 125,000,000, TimeBase = 3
            nTimeBase = (uint)(FACBASE / Rate) + 2;
            //1S采集（Rate = 125M）個點數，1個周期采集2.5M個樣本250W，上傳到電腦2500000/downSampleRatio（1000） = 2500個數據
            buffLen = (int)(Rate / signalPeriod); 
        }

 

 

在公共類CSettingPico里定義公開方法 

調用了上一步定義的方法，計算得出了數組的長度

       /// <summary>
        /// 得到存放最大值最小值數組的長度
        /// </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; //在觸發事件之后返回的樣品個數，注意不是降采樣后返回的，而是pico采集的實際樣品個數
            }
        }