Analog Filter - Keithley 2001 Operator's Manual

annunciator off, the digital filter for that function is
completely disabled.
The state and configuration of the digital filter for each
function is saved when changing functions.
• Pressing the FILTER key to enable the filter
momentarily displays one of the following typical
messages:
Filter Enabled
Digital = AVG(10)
or
Filter Enabled
Digital = ADV(10)
or
Filter Enabled
Digital = AUTO
where: AVG is the averaging filter.
ADV is the advanced filter.
AUTO is the type listed in
(10) is the number of reading conversions to average.
3.9.7

Analog filter

The Model 2001 has an analog filter for use with the DCV
function. This filter reduces the number of overflow errors
caused by noise seen on the input signal. The analog filter is
most effective when measuring voltages greater than 2 Vp-p
frequencies ranging from 10kHz to 1MHz.
Controlling the analog filter
Perform the following steps to enable or disable the analog
filter:
1. Press CONFIG and then DCV to display the DCV con-
figuration menu.
2. Place the cursor (using  and keys) on ANALOG-
FILTER and press ENTER to display the control options
(ON or OFF). Cursor position indicates the present state
of the analog filter.
3. To change the state of the analog filter, place the cursor
on the alternate state and press ENTER.
4. Use the EXIT key to back out of the menu structure.
2001-900-01 Rev. K/ August 2010
Table 3-36.
The FILT annunciator on the display only
indicates the state of the digital filter. It is
not used for the analog filter.
Selecting the first multiple (NEXT) display for DCV enables
the analog filter. Leaving this multiple display returns the
analog filter to its previous state.
Analog filter characteristics
Figure 3-41, part A provides a simplified block diagram of
the Model 2001 showing the location of the analog filter.
When enabled, it provides a "cleaner" signal to the
preamplifier. As a result, readings are less noisy. The analog
filter does not affect any of the instrument's specifications
beyond those dealing specifically with the filter function.
The analog filter is a single stage, single-pole, low-pass RC
network that rolls off the signal at an approximate rate of
20dB per decade above the cutoff frequency of 10kHz. The
analog filter has a zero at 600kHz.
the general frequency response for the analog filter.
The analog filter is most effective on the 2V or 20V range
with line synchronization enabled. On the 200mV range, a
noisy input signal may cause overflow readings even though
the analog filter is enabled.
Front Panel Operation
NOTE
Figure 3-41, part B shows
3-91