Philips PM 6303 - 1.4.2. Measuring principle

E
1-8
1.4.2. Measuring
principle
The
measurement
principle
is based
on the so-called
current and
voltage
measurement
technique:
the
component
voltage
and after
that the
component current
are measured.
The
measured
values
are
con-
verted
to binary
numbers.
From these
numbers
the CPU
computes
the
CUT
parameter
of
interest.
According
to the
front
panel
parameter
selection, either
the
dominating
component
-resistance,
capa-
citance
or
inductance—
or
one of
the other selectable
parameters
is
displayed.
Each measurement
cycle lasts
approx. 0.5 s. It comprises 5 single
measurements,
the
results of
which
are stored in the
microprocessor data memory,
a
subsequent
arithmetic
evaluation
and
a final transfer
of the result to the
display.
The 5
single measurements
are as follows:
1. Reference
measurement:
At the beginning
of each measurement
cycle
a
reference measurement
is performed,
whereby
the input
of
the programmable
amplifier is short-circuited.
The counter contents
of the
A/D
conversion
at the
end
of this measurement
serves as reference for the subsequent
4 measurements.
2.
0°
voltage measurement
The voltage
at the
CUT
is measured.
The switching
phase of
the
phase
sensitive rectifier is
0°,
3.
90°
voltage measurement:
The voltage
at
the
CUT is measured.
The switching phase of
the phase sensitive rectifier is
90°.
4.
0°
current
measurement*
-
The inputs
of the
differential amplifier are
switched over to the
output of the current
to
voltage conver-
ter.
The
current
through the
CUT is measured.
The switching
phase of the phase sensitive
rectifier is
0°.
5.
90°
current
measurement:
The
current through
the CUT is measured.
The
switching phase
of the phase
sensitive
rectifier
is
90°.
At the end of the
5 single measurements
the 5 corresponding binary
numbers
of the
A/D conversions
and the assigned
gain factors
are stored in the microprocessor
data
memory. From
this the
micropro-
cessor first
calculates the equivalent
series resistance
Rs, the equivalent
series reactance
Xs and
the
quality
factor
Q
=
Xs/Rs
of the
CUT. In the RCL
AUTO mode the
microprocessor
determines the
dominant
component, either
Rs resp.
Rp, Cp or Ls, calculates
its value, dimension
and
equivalent-
circuit
symbol
by arithmetic routines
and transfers the result
to the display.
If
one
of the
8
other
para-
meters is selected
by the
step keys this parameter is
calculated and
displayed.
After that
the micropro-
cessor starts the
next measurement
cycle with the single measurement
routines.