Range Holding - IET Labs, Inc. RLC Digibridge 1693 User And Service Manual

1693 RLC Digibridge
NOTE: If the measured value is very small (even
below one count) or very large (even over 99999),
high resolution measurements are possible using the
ratio display. Refer to paragraph 3.3.6 or 3.10
High Overrange. The "high" extension of the high
range goes up to the maximum display (all 9's, with
the decimal point at the right), and finally to blank,
with reduced accuracy. The high overrange is used
for the very large values of RLC that exceed the basic
high range.
Autoranging. Autoranging is normal; it is inhibited
only if you select RANGEHELD. There is a slight
hysteresis in the changeover from range to range to
eliminate a possible cause of display flickering.
Time Required to Change Range. The Digibridge
must almost complete a measurement cycle in the
previously established range before starting measure-
ment in the range to which it changes. The Digibridge
completes the data acquisition and a large part of the
calculation process before "deciding" whether the
present range is best for the measured value. (If you
have selected "median value", a special function,
the Digibridge will go through basically three mea-
surement cycles so that it has the median value for
making the decision whether to change ranges.) Thus,
measuring a lot of components that straddle a range
boundary requires almost double the regular mea-
surement time for every DUT that is on the opposite
side of the boundary from its predecessor. (Note : if
the Digibridge starts in range 1 to measure in range
4, four almost complete measurement cycles are re-
quired before the desired result appears.) Therefore
(at least in some measurement situations), maximum
measurement speed requires range holding.

3.5.7 Range Holding

Why Hold Range? The most important use of the
range holding capability is to avoid range changes
when the component is removed from the fixture
when in the CONTINUOUS mode. With no compo-
nent connected, the instrument will autorange to range
1. Thus, if range 1 is not selected when the component
is in place, considerable time is lost by unnecessary
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autoranging. Another use of the range hold occurs
when measuring components of the same nominal
value whose actual values spread across the bound-
ary between two ranges . If allowed to autorange, the
units and decimal point may change with range which
may be confusing to the operator. There are other
uses for holding a range, such as obtaining the correct
bias current or getting better guard capability. When
a range is held that is not the range that autoranging
would select, the accuracy may be sacrificed (see
paragraph 3.6.9).
To inhibit autoranging, select the "range held" mode
(RANGE HELD indicator lit) as described below -
four methods.
To Hold Present Range. If the present range (as indi-
cated by the measurement display) is the desired one,
press [SHIFT][HOLD RANGE] to light the RANGE
HELD indicator. (To return to the normal autoranging
feature, press the same two keys again, making the
RANGE HELD indicator unlit.)
To Hold the Range of a Sample DUT. One way to get
into the desired range is to measure a DUT known to
be in that range, thus:
1. Measure the DUT as usual.
2. Verify that the desired range is confirmed by
the measurement display.
3. Press: [SHIFT][HOLDRANGE] to light the
RANGE HELD indicator.
(To return to the normal autoranging feature, press
the same two keys again, making the RANGE HELD
indicator unlit.)
Operation