Filters - Keithley 486 Instruction Manual

SECTION 3
Front Panel Operation
when zero correction is performed, only the present
range is zero corrected. Before making measurements, it
is recommended that each current range be zero cor-
rected. The zero corrected value for each range is "re-
membered". The zero corrected values can be retained as
default conditions on power up (see paragraph 3.8.6).
For best measurement accuracy, zero correction should
be performed any time a settled zero checked display is
not readingzero. Notethatzerocheckdoessnot havetobe
enabled to perform zero correction. The instrument will
automatically zero check the input before performing the
correction.
Perform the following steps to perform zero correction:
1. Enable zero check and allow the displayed reading
to settle.
_ .
2. To perform zero correction, press SIGT and then
CORRECT in that order. The following
message
will
be displayed while zero correction is in process:
CORRECl-ING
After correction, the instrument returns to the normal
measurement display state. Zero check will be on only if
it was enabled in step 1.
Enabling zero check with a REL baseline established (see
paragraph 3.5.5) will remove the applied signal from the
input with a displayed reading as follows:
Displayed reading = input signal-relative baseline
= 0 -relative baseline
=-relative baseline
Performing zero correction wiII cancel (zero) only the
measured offset.
Note: In the V/I ohms hmction, the ZERO CHECK indi-
cator will flash if zero check is enabled. In zero check, the
displaywiUblsnk(-----KS&
3.54
Filters
SHIFT FILTER
El
FILTER
Filtering is used to stabilize noisy measurements. The
Model 486/487 has two available filters; a digital filter
and an analog filter. The digital filter is a function of
measurement conversions. It bases the displayed (or
stored) reading on the weighted average of a number of
measurement conversions. The analog filter is a simple
RC filter whose time constant varies with the selected
range. It affects the rise time and settling time of the
measurement (see Table 3-6). Rise times are defined as
the time it takes the measurement to go from 10% to 90%
of its final value of a step change. Settling time is the total
time it takes the measurement to reach its final value
(within 0.1%).
When the filter is enabled, the selected filter(s) (digital fil-
ter, analog filter or both) will be used. Filter is enabled by
simply pressing PILTER (FILTER indicator will turn on).
PressingFILTERthesecondtimewilldisablethefilterk).
Perform the following steps to check or change the filter
selection:
Table 3-6. Analog Filter Effects
;
56msec
17msec
6msec
2msec
7Omsec
12msec
4msec
2msec
tbled
settling
Time
333msec
56msec
17msec
6msec
2msec
2OlStX
2msec