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3.3.6 Ratio Displays, Virtual Range
Extensions, and Conductance
Measurements
The Digibridge can easily be programmed to display
the principal test result (R, L, C, G, Z, Y) in the form
of a ratio instead of the actual measured value. The
ratio is either (measured value / stored nominal value)
or the reciprocal of that. By suitable choice of the
nominal value, you can obtain virtual range exten-
sions for measurement of very large values or for
fine resolution in measurement of very small values.
One use of the ratio display capability is to obtain
results in terms of a multiple of some reference,
which can be obtained if desired by measuring a real
reference DUT.
For Very Large R, L, or G. Another use of the ra-
tio display is to obtain measurements of very high
values (in high overrange, i.e., exceeding 99999
of the highest range). For example, consider the
measurement of capacitors with values near 200 mF
[i.e., 0.2 farad). Any value greater than 99999 µF
(99.999 mF) normally causes a blank display (because
the unit multiplier on the highest C range is fixed and
the display is limited to 5 digits).
However, if you enter a nominal value of
1000 µF, and enable calculation and display of the
ratio "measurement/nominal", then measurement
results can be interpreted as though they were in
units of mF (although the ratio is really dimen-
sionless and the unit indicators remain unlit) . In
this example, the measurement results can then be
199.99, 200.00, 200.01, etc. For much larger ca-
pacitance the Digibridge will automatically move
the decimal point, up to 99999 mF [i.e., 99.999
farads). For still larger values, you can make the
nominal value larger.
For Very Small R, L, or C. Another use of the ratio
display is to obtain better resolution of very small
values (Otherwise the resolution can be no better than
.00001 on the lowest range.) For example, consider
the measurement of some inductors with values near
20 nH. Because the minimum measured value, and
Operation
the resolution limit also, is .00001 mH. the normal
measurement results can only be .00000, .00001,
.00002, .00003 mH. etc, i.e., steps of 50% of the
20 nH value . However, if you enter a nominal value
of .001 mH. and enable calculation and display of the
ratio "measurement /nominal", then measurement
results can be interpreted as though they were in units
of µH (although the ratio is really dimensionless and
the unit indicators remain unlit). In this example,
the measurement results can then be .01999, .02000,
.02001, etc, i.e., steps of .05%, which is very fine
resolution. By selecting a sufficiently small nominal
value, you can obtain resolution that is better than the
repeatability of measurements.
Procedure. To program the Digibridge for ratio
displays: enter desired nominal value in appropriate
units of measurement; enable the special function,
as follows.
1. With the [FUNCTION] key, select ENTER.
2. Using the appropriate parameter key, select
the units of the nominal value to be stored.
If the Digibridge has just completed a measurement of a
DUT, so that the principal display already indicates the
appropriate units of measurement, Step 2 can be skipped.
3. Enter the desired nominal value. For ex-
ample, if the units displayed on the panel are
µF and you want to set up a ratio display that
[l][0][0][0][=][SHIFT][NOM VALUE]
can be interpreted as mF, press:
4. Enable the desired special function, the per-
tinent commands are:
• To display measurement/nominal: [2][=]
[SHIFT][SPECIAL][6]
• To display nominal/measurement: [1][=]
[SHIFT][SPECIAL][6]
• To disable ratio displays: [0] [=] [SHIFT]
[SPECIAL] [6]
If ratio is selected, the 'RATIO" indicator will light on
the display window
5. To enable measurements, select MEASURE
with the [FUNCTION] key.
6. To display the ratio in the left-hand display
area, select VALUE with the [DISPLAY] key.
1693 RLC Digibridge
41
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