Fluorolog-3 v. 2.2 (10 Sep 2002)
Optimizing Data Acquisition
4-14
Note:
This table is only a
guide
. The optimum inte-
gration time for other
measurements, such as
time-base, polarization,
phosphorescence lifetimes,
and anisotropy, may be dif-
ferent.
Determining the optimum integration time
The length of time during which photons are counted and averaged for each data point is re-
ferred to as the
integration time
. An unwanted portion of this signal comes from noise and
dark counts (distortion inherent in the signal detector and its electronics when high voltage is
applied). By increasing the integration time, the signal is averaged longer, resulting in a bet-
ter
S
/
N
ratio. This ratio is enhanced by a factor of
t
1/2
, where
t
is the multiplicative increase
in integration time. For example, doubling the integration time from 1 s to 2 s increases the
S
/
N
ratio by over 40%, as shown below:
For an integration time of 1 second,
S N
t
/
/
/
=
=
=
1 2
1 2
1
1
For an integration time of 2 seconds,
S N
t
/
.
/
/
=
=
≈
1 2
1 2
2
1414
or approximately 42%. Because
S
/
N
determines the noise level in a spectrum, use of the ap-
propriate integration time is important for high-quality results.
To discover the appropriate integration time:
a
Find the maximum fluorescence intensity by acquiring a preliminary scan, using
an integration time of 0.1 s and a bandpass of 5 nm.
b
From this preliminary scan, note the maximum intensity, and select the
appropriate integration time from the table below.
Signal intensity
(counts per second)
Estimated integration time
(seconds)
1000 to 5000
2.0
5001 to 50 000
1.0
50 001 to 500 000
0.1
500 001 to 4 000 000
0.05
Integration time can be set either through
Run Experiment
for a specific experiment,
Real Time Display
to view the effects of
different integration times on a spectrum, or
Visual Instrument
Setup
to establish a
default for all experiments. Refer to the
software manual to learn more about setting
the integration time.
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