IET Labs, Inc. RLC Digibridge 1693, User And Service Manual, Page: 82 / 171

58
1693 RLC Digibridge
Operation
where Krange is: for range 1, 1; for range 2, .0625;
for range 3, .0040; for range 4, .00024. Factor f is
frequency in kilohertz. Csn is total capacitance from
the low [IL and PL) terminals to ground (in cable and
test fixture, beyond the “normal DUT interface” - see
notes above and below).
NOTE: If the 7000-05 tweezers (or other extension
having capacitance of about 200 to 300 pF) is con-
nected directly to the 1693 Digibridge (without any
other cable) the difference from “normal DUT inter-
face” is trivial, and Ald error is negligible.
If Ald is significant, one can calculate and use it to
correct each measured C, L, or (if the DUT is a resis-
tor) R. The effect on D or Q is negligible.
For C, the Digibridge reads high; use a negative
correction.
For L or R, the Digibridge reads low; use a positive
correction.
The following table is used in the preceding formulas:
Cable R Lc* Csn
1689-9602 bnc Cable, with 1689-9600
Remote Test Fixture
.33 Ω 1.1 µH 0 pF
1657-9600 Extender cable with banana
plugs
.37 Ω 2.20 µH 475 pF
* The formulas for Acm and Acmx contain x, which is
2(pi)fLc, where pi is 3.1416, where f is expressed in Hz,
and inductance Lc is tabulated above.
Table 3-13: Typical parameters for Digibridge
Extender Cables
Refer to Table 3-14 for some representative examples
of accuracy (error) terms related to cables, for certain
range and frequency selections. Notice that the ad-
dition of an)’ unspecified cable and/or “homemade”
remote test fixture will probably increase each of these
parameters and error terms. Also, cable and test fixture
capacitance can aggravate a resonance problem in
measurement of large values of inductance at high
frequency; refer to paragraph 3.13.
Accuracy
Term*
1657-9600
Banana
1689-9602
bnc-to-bnc
Units
Acmx for 1kHz .00069/Xdut .00034/Xdut % of Ls or Cs
Acmx for 20kHz .0069/Xdut .0088/Xdut % of Ls or Cs
Acmr any
frequency
.002/Rsdut .020/Rsdut % of meas Rs
Range 1, 1kHz
Zero ** .00021 % of meas
value
Range 1,
20kHz
Zero ** .084 % of meas
value
Range 2,
20kHz
Zero ** .0052 % of meas
value
Range 2,
100kHz
Zero ** .13 % of meas
value
Range 3,
20kHz
Zero ** .00033 % of meas
value
* Xdut and Rsdut represent the DUT’s series reactance
and resistance respectively
** Ald error is significant only for extension beyond
“normal DUT interface”, where the system software
applies compensation.
Table 3-14: Typical Cable-Related Accuracy
(Error) Terms
3.6.8 Use of Signal Reversing
(Special Function) for Tests at
Power Frequencies
The special “signal reversing” function is primarily
for use whenever the test frequency is 60 or 120Hz
(if your power frequency is 60 Hz) or whenever it
is 50 or 100 Hz (if your power frequency is 50 Hz).
However, it is also useful whenever the test frequency
is equal to or very close to the frequency of any con-
stant external signal that can be coupled to the low
terminal(s) of the DUT (IL and PL).
If this disturbance is strong enough, it can degrade the
accuracy of normal measurements. However if the
disturbance is not so very strong that the Digibridge
sensing circuits are overdriven, then “signal revers-
ing” will typically restore specified accuracy. This
special function enables a test routine in which the
phase of the test signal is periodically reversed and the
Digibridge senses both phases additively. However,
the constant- phase disturbance component of the
sensed signal is canceled by subtraction. This capa-
bility is a special function. To enable it, press [1][=]
[SHIFT][SPECIAL)[3).
To disable “signal reversing”, for fastest measure-
ments, press [0][=][SHIFT][SPECIAL][3].