Symptoms Likely To Mislead - HP 4262A Operating And Service Manual

Section VIII
Table 8-2
Model 4262A
Table 8-2. Symptoms Likely to Mislead.
Category Symptoms
Probable cause
L MEASUREMENT
When LCR RANGE setting is in AUTO,
the range is shifted altemately up and
down between two ranges and does
not settle on a specific range.
Measured values differ depending on the
range selected.
This symptom occurs when the induc-
tance of an inductor with core changes
because of the current flowing through
the coil.
Permeability of inductor core changes
with measurement signal level (current),
which differs for each range. (Measure
in MANUAL ranging mode.) See Note
below.
Measured values differ depending on
the selected test signal frequencies.
Specifically, a large difference exists be-
tween the measured value at 120Hz and
that at another test signal frequency.
This symptom is because of a difference
in the permeability of the inductor core
developed by two different measure-
ment frequencies.
C MEASUREMENT
When measuring a small capacitance at
120Hz test signal frequency, measured
counts on the LCR DISPLAY fluctuates
by several counts.
Interference of ac frequency hum
noise. Check for any ac line cables
close to the test leads. Check for
grounding of the instrument chassis.
R MEASUREMENT
Both LCR and D/Q DISPLAYS are
blank ( - - - ) with respect to the sample
connected to the UNKNOWN terminals.
The DUT is a wirewound resistor having
a large inductance. (Note that some
standard resistors are used only with dc
current and their calibrated values are
so certified.)
Common to
all LCR
MEASUREMENTS
When measuring an inductance, capa-
citance or resistance of a large value, a
measurement error over the specified
limits occurs.
C OFFSET control (related to induct-
ance and resistance measurements) or L
OFFSET control (related to capacitance
measurement) is misadjusted.
Note: For example, if value of sample is 187.0uH on the 100uH range, the auto ranging
function moves to 1000uH range. Then the sample may develop a lower induc-
tance at the applied measurement signal on the 1000uH range. It may, for example,
develop an inductance of 160.0uH that is suitable for measurement on 100uH range.
The range will again be reset to the 100zH range and, as a result will repeat (auto
range) up and down between the lower and the higher ranges.
8-18