IET Labs, Inc. RLC Digibridge 1693, User And Service Manual, Page: 126 / 171

102
1693 RLC Digibridge
Operation
3.13.2 Failure Display due to Signal
Overload
“014” (right display blank) Occurrence of an unrecov-
erable signal overload during the last measurement.
This means that a signal overload occurred during
RANGE HELD or while measuring on Range 4.
Otherwise (if a signal overload occurs on range I, 2,
or 3 and range is NOT held), this failure display is
not shown; instead, the Digibridge will change to the
next higher-numbered range and try again.
Signal overload can result from any of five causes:
• RANGE HELD and CONSTANT VOLTAGE
with impedance value too low for the range.
• Transient voltage from charged capacitor.
• Transient due to application of bias voltage.
• Hardware failure.
• LC resonance effect (measuring inductance).
3.13.3 Failure Display due to
Abnormal Measurement Cycle
22222 zzzz . The Digibridge will abort the measure-
ment and provide this display if there is (even once
during a measurement) a converter/detector malfunc-
tion such that the integrator’s conversion cannot be
completed. There are two versions of this failure.
22222 2222 . The cycle is “too long”. Integrator volt-
age does not return to zero in reasonable time.
22222 1111 . The cycle is “too short”. Integrator
voltage was already zero (or wrong polarity) when
conversion began.
3.13.4 Failure Display due to LC
Resonance
A display of “0 14” or 22222 1111 can occur, in
place of the expected L and Q, because the inductor
being measured resonates with measuring circuit ca-
pacitance. (Resonance can cause an overload of the
converter/detector.) The Digibridge thus presents an
easily noticed failure display rather than an invalid
measurement result.
When Expected.
This resonance effect can be expected
when large values of inductance are being measured
at high frequency. In particular, if the Digibridge is
autoranging, this effect can be expected in range 1
under any of the following 4 equivalent conditions.
(A representative value of L that will cause selection
of range 1 is indicated in parentheses beside each
condition.)
• Without extender cable: f > 3.8 kHz (L > 1 H
at 4 kHz).
• With 1657-9600 cable (banana plugs): f > 1.1
kHz (L > 3 H at 1.2 kHz).
• With 1689-9602 cable (BNC/BNC): f > 2 kHz
(L > 2 H at 2 kHz).
• With any other cable and remote test fixture,
use the following formula: f > 770 / (200 + C).
where f is in kHz, C is stray capacitance outside of
the Digibridge, from the high (Ih, Ph) terminal to
ground (guard), expressed in pF. (Measurement will
be on range 1 if L > 4/f.)
This resonance effect can also be expected under some
conditions of high-frequency measurement with range
1 held but the inductance of the DUT appropriate for
range 2. The effect is NOT expected with autoranging
in ranges 2, 3, 4, unless stray capacitance is consider-
ably larger than that of the 1657-9600 extender cable.
It is possible for valid measurement, with a slight
reduction in accuracy, to be made under conditions
very close to those that will trigger the LC resonance
failure display. Such a measurement can be expected
to meet accuracy specifications if it is displayed at all.
Recommended Procedure
. If this LC-resonance
failure display appears, in the course of otherwise
normal measurements, the instrument is functioning
normally. Valid measurements can usually be made
by taking one or more of the following steps:
1. Select low source impedance, by pressing
[SHIFT][CONST VOLTAGE] so that the
CONSTANT VOLTAGE indicator lights up.
2. Select a low-impedance range. For example,
if measurement is normally in range 1, try
holding range 2; or if range 1 has been held,
select autorange.