Typical Minimum Usable Scan Intervals - Keithley 199 Instruction Manual

BASIC OMM OPERATION
2.11.4 Scanner Delay
A channel settling time can be incorporated by program-
ming the scanner delay with the TRIG SETUP key. When
a scanner delay is used, the instrument wiIl wait the pro-
grammed delay period~after closing a channel before tak-
ing a readingThus, the delay period is essentially a chan-
nel settling time to allow signals to settle before each
measurement.
The scanner delay (settling time) in the range of Omsec to
999.999sec can be programmed using TRIG~SETUP as
follows:
1. Press TRIG SETUP and then NEXT, and note that the
instrument displays the following:
DELAY=
Followed by:
000.000 s
2. Key in the desired delay period in the range of 0 to
999.99sec.
3. Press NEXT once to advance to the interval selection
menu,
or press NEXT twice to return to normal display.
NOTES:
1. A scanner delay of at least one second should be used
when measuring AC signals. This recommendation is
based on allowing the measurement to settle to withii
0.1% of the final value.
2. The programmed interval must be longer than the delay
to avoid the "INTERVAL OVERRUN" error.
2.11.5 Using Filtering with the Scanner
The Model 199 uses the running average type of filtering.
When the front panel filter is on (FLTR on), additional
averaging is used, as discussed in paragraph 2.6.3. For that
reason, the reading rates are slower when the front panel
filter is enabled.
For normal (non-scanner) operation, the display still up-
dates while the filtering process is still going on. Under
these conditions, the FLTR light blinks until the final,
filtered reading is being displayed. With scanner opera-
tion, however. the unit will not advance to the next chan-
nel until the final, filtered reading has been taken. Thus,
the maximum scan rates available will be slower with the
filter on than with it turned off.
The instrument will advise you if you have exceeded the
maximum scan rates. In the continuous trigger mode, the
"INTERVAL OVERRUN" message wiIl be displayed if the
programmed interval is too short for the present instm-
ment contiguration. In teh one-shot bigger mode, the unit
will display the 'TRIGGER OVERRUN" message if it iS
still processing a reading when triggered.
2.11.16 Minimum Scan Interval Times
As discussed previously, the minimum usable interval
depends on the function, range, resolution, as well as the
multiplexer and fflter states. Table 2-7 summarizes typical
minimum interval times for various ranges and fimctions.
Programming the instruments for shorter times will result
in the "INTERVAL OVERRUN" message, in which case the
unit will scan slower than the programmed interval.
Times for both the STEP and SCAN modes are given at
both 4% digit and 5Yz digit resolution (where applicable),
and all times are with internal filter on (FITR off) and MUX
ON. For DC and ohms functions, turning the internal Biter
off (using POX tier the bus) and mutiplexer off will shorten
the times somewhat; times will typically be about lo-30%
shorter with the multiplexer and filter off. Conversely,
operating the instrument with the front panel filter on
(FLIR on) will increase
the
minimum interval times.
Table 2-7. Typical Minimum Usable Scan Intervals
Function
30V DC
3V AC
3OOQ
3OOkB
3Mt-l
3OMO
34OMl-l
3OmA D(
3A AC
ACV dB
ACA dB
STEP Mode
4% Digit 5% Digit
I
20msec 680msec
20msec 35msec
60msec 590msec
-
7OOmsec
-
1.3sec
I
-
5.lsec
-
7sec
20msec 380msec
2Omsec 35msec
46msec -
37msec -
T
SCAF
4% Digil
EOmsec
l50mec
47Omsec
-
-
-
EOmsec
l5omsec
360msec
360mkc
diode
i% Digit
2.lsec
27Omsec
2sec
4.9sec
6.2sec
32sec
65sec
2.lsec
270msec
NOTES:
1. All times are typical.
2. Times shown are with FLTR off, MUX ON.
3. Scan mode times are with eight-channel limit.
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