27-08-2012, 10:38 AM
Handyscope HS4 DIFF
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Introduction
Many technicians investigate electrical signals. Though the mea-
surement may not be electrical, the physical variable is often con-
verted to an electrical signal, with a special transducer. Common
transducers are accelerometers, pressure probes, current clamps
and temperature probes. The advantages of converting the physical
parameters to electrical signals are large, since many instruments
for examining electrical signals are available.
The Handyscope HS4 DIFF is a portable four channel measuring
instrument with dierential inputs. The Handyscope HS4 DIFF
is available in several models with dierent maximum sampling
frequencies: 5 MS/s, 10 MS/s, 25 MS/s or 50 MS/s.
Dierential test lead
The Handyscope HS4 DIFF comes with a special dierential test
lead. This test lead is specially designed to ensure a good CMRR.
The special heat resistant dierential test lead provided with the
Handyscope HS4 DIFF is designed to be immune for noise from
the surrounding environment.
Sampling
When sampling the input signal, samples are taken at xed inter-
vals. At these intervals, the size of the input signal is converted to a
number. The accuracy of this number depends on the resolution of
the instrument. The higher the resolution, the smaller the voltage
steps in which the input range of the instrument is divided. The
acquired numbers can be used for various purposes, e.g. to create
a graph.
Sample frequency
The rate at which the samples are taken is called the sampling
frequency, the number of samples per second. A higher sampling
frequency corresponds to a shorter interval between the samples.
As is visible in gure 3.8, with a higher sampling frequency, the
original signal can be reconstructed much better from the measured
samples.
Digitizing
When digitizing the samples, the voltage at each sample time is
converted to a number. This is done by comparing the voltage
with a number of levels. The resulting number is the number cor-
responding to the level that is closest to the voltage. The number
of levels is determined by the resolution, according to the following
relation: LevelCount = 2Resolution.
The higher the resolution, the more levels are available and the
more accurate the input signal can be reconstructed. In gure 3.10,
the same signal is digitized, using two dierent amounts of levels:
16 (4-bit) and 64 (6-bit).