That is to be expected. When you acquire multiple points, the Write to Measurement File is going to use the dt of the waveform to calculate the time between samples and writes that to the file. When you use a single point acquisition, the waveform has a single value so there is no dt to calculate. The 0 in the file is a result of this. The Write to Measurement File would require extensive modifications to write the delta between the t0 values being passed instead of from the dt and number of samples. You can open the block diagram of Write to Measurement to see if the modification is something you would want to tackle. Otherwise, you can keep track of the elapsed time between single samples with a shift register and the tick count function, for example. Then you could use the Write to Spreadsheet or at an even lower level, Write to Text File.
