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SensL © 2011
13
USER MANUAL
HRM-TDC
SensL © 2011
13
> Hrm-tdc System Description > Hrm-tdc Specific Feature Overview
HISTOGRAM
Histogram modes use consecutive memory locations to store counts that represent points on a graph. These
memory locations or
time bins
are incremented based on the value of a time measurement. Each memory location
represents a time range equal to the resolution of the timer. Within the HISTOGRAM category there are two distinct
modes of operation, single-stop and multi-stop.
Single-stop histogram
Following a START event,
the first
stop event is measured and the corresponding time bin is incremented. This is
repeated to build up a histogram (curve) in memory showing the distribution of 1st events following a start input.
This mode is also referred to as “TCSPC” mode due to its application in Time Correlated Single Photon Counting.
Multi-stop histogram
Following a START event,
all stop
events are measured and their corresponding time bins incremented. The next
START input will reset the timer and the following events processed again. This is repeated to build up a histogram
in memory showing the distribution of STOP events following a START input. This mode is also referred to as
“Multiscaler/Counter” mode.
FIFO
FIFO modes continually record the timing of events and save the results in consecutive locations in memory. When
the last location in memory is filled, if not commanded to stop, the module continues to record data starting at the
beginning of memory again. The host PC, via the USB interface, keeps up in time with the module, reading the data
from memory to a file in the host computer. Hence the memory can be regarded as a very large FIFO. Providing the
host PC can keep up with the module, timing data can be recorded indefinitely. Within the FIFO category there are
two distinct modes of operation, single-stop and multi-stop.
Single-stop FIFO
In this mode the module carries out the single-stop histogram process as described previously. However, along with
the single-stop measurement, the information stored in the FIFO also has a
MACRO time
that defines what time
during the experiment the timing measurement was made. This mode is also referred to as “TCSPC with Macro
time”.
Multi-stop FIFO
This mode is also referred to as “FIFO time tagging” and offers 2 options:
Free Running:
Using this option the process is started with a single start pulse. The module will then fill the memory with time
tags defining the time of each stop event with relation to the initial single start pulse. Any further Start inputs will
be ignored.
Resync:
This option uses a 250KHz clock output from the module as the Start input. The clock continuously re-
synchronizes the module to eliminate long term drift between channels. This is the preferred method when it is
required to compare the data from more than one channel.