Cornelius DPC 230 Specifications download pdf (Page 50)

44 SPCM Software

next reference pulse (see ‘Relative Timing’, page 3). The data of the detector channels can be

interpreted either as single waveforms (‘Single’), as oscilloscope traces (‘Oscilloscope’), or as

fluorescence decay curves plus fluorescence correlation data (‘FIFO’). The ‘FIFO’ option is

similar to the FIFO mode of the bh SPC modules [2]. Moreover, images can be acquired by

recording synchronisation pulses from a scanner together with the photons (‘FIFO Image’).

Please note that ‘TCSPC’ is available only for the CFD inputs.

Multichannel Scaler

The ‘Multiscaler’ mode records both relative and absolute photon times. The times are re-

ferred to a reference pulse from a light source (see ‘Multichannel Scaler Mode’, page 8). In

contrast to ‘TCSPC FIFO’ every reference pulse is rescored, not only the next one after the

detection of a photon. The times are measured from the reference pulses to the photons. The

‘Single’ option accumulates the photon density over the time after the reference pulses, i.e.

builds up the waveform of the light signals. The ‘Oscilloscope’ mode runs a repetitive meas-

urement and displays subsequent waveforms in short intervals. ‘FIFO’ is used when fluores-

cence correlation in combination with photon density histograms is required. Images can be

acquired by recording synchronisation pulses from a scanner together with the photons (‘FIFO

Image’). The ‘Multiscaler’ function is available both for the CFD inputs and for the LVTTL

inputs.

Specification of the Time-Tag Date File

The DPC-230 records time-tagged data, i.e. the times and TDC channel numbers of the indi-

vidual photons. From these data can be calculated waveforms, intensity traces, correlation

curves, or images. Because these data operations are performed online on the incoming data

stream the time-tag data need not necessarily be saved in a file. However, it may be useful to

save the time-tag data, e.g. to be able to re-analyse the data later, or to import them into other

analysis software. Therefore, the time-tag data can be stored in two data files, one for TDC 1,

the other for TDC 2. For data format please see ‘Format of Time-Tag Data Files’, page 55.

The corresponding control section of the system parameters is shown in Fig. 72.

Fig. 72: Options for saving the raw data

The time-tag data recorded by the DPC-230 can easily reach sizes of tens or hundreds of

megabytes. The maximum used disk space can therefore be limited by activating the ‘Limit

Disk Space’ button and specifying the maximum file size. The measurement stops when the

specified disk space has been filled.

‘Maximum Buffer Size’ defines a buffer in the computer memory. The buffer stores the data

before they are saved to the hard disk. If possible, the buffer should be large enough to buffer

the FIFO data of the complete measurement. Usually, the buffer size can be as large as

250 Mb for a computer with 1 Gb RAM. Under no circumstances a buffer size larger than the

available memory space of the computer should be used. Windows may then attempt to pro-

vide virtual memory, i.e. to swap memory space with the hard disc. This makes the computer

extremely slow and almost certainly causes problems with the data transfer from the DPC

module.

If a sufficiently large buffer is not available use a buffer smaller than the value specified under

‘limit disk space’. Of course, the SPCM software writes to the hard disk when the buffer is

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Cornelius DPC 230 Specifications Page 50

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