Keithley 6512, Instruction Manual

Page: 46 / 156

Operation
2-26
The baseline maintains its absolute value regardless of range.
For example, if a 1V signal is suppressed on the 2V range, it
will remain at 1V on the 20V and 200V ranges. Only one
reading for the presently selected function can be sup-
pressed; the value will be lost if the function is changed.
The suppressed readings can be as small as the resolution of
the instrument will allow, or as large as full range. Some typ-
ical examples include:
Suppressed Applied Displayed
Reading Signal Value
+10.500V +18.600V +8.100V
+2.556nA +1.8000nA -0.7560nA
-12.600mA +4.500mA +17.100mA
To use suppression, perform the following steps:
1. Cancel suppress if presently enabled.
2. Select a range and function that is consistent with the an-
ticipated measurement.
3. Connect the signal to be suppressed to the instrument input.
WARNING
With suppress enabled, the voltage on
the input terminals may be significantly
larger than the displayed value. For ex-
ample, if a 150VDC baseline is stored,
an applied voltage of +175V will result
in a displayed value of only +25V.
4. Press the SUPPRESS button. The triggered reading will
be stored at that point.
5. Disconnect the suppressed signal from the input, and
connect the signal to be measured in its place. Subse-
quent readings will be the difference between the sup-
pressed value and the applied signal.
6. To return the instrument to the normal mode, press the
SUPPRESS button. The SUPPRESS light will go off,
and the instrument will be taken out of the suppression
mode. The previously stored suppressed value will be
cancelled.
NOTES:
1. Using suppress reduces the dynamic range of the mea-
surement. For example, if the suppressed value is
100mV on the 200mV range, an input voltage of 100mV
or more will over-range the instrument even though in-
put voltages up to 199.99mV are normally within the ca-
pabilities of the 200mV range. If the instrument is in the
auto-range mode, it will move up range, if necessary.
2. Setting the range lower than the suppressed value will
over-range the display; the instrument will display the
“OL” message under these conditions.
3. To store a new baseline, suppress must first be disabled
and then enabled once again. The new value will be
stored with the first triggered conversion.
4. Do not move the instrument down range when using
suppress.
2.11 Data storage
The Model 6512 has an internal 100-point data store mode
that can be used to log a series of readings. The fill rate of the
data store buffer can be set to specific intervals by a parame-
ter that is entered when the storage mode is first enabled. Al-
ternatively, a special one-shot trigger mode can be used to
control the fill rate from the front panel. Once data is stored,
readings can be easily recalled from the front panel.
Minimum and maximum values can also be retained for fu-
ture recall. As long as data store is enabled, maximum and
minimum values are updated with each reading conversion.
Enter the data storage mode as follows:
1. Press and hold the DATA STORE ON/OFF button. The
instrument will then scroll through the various reading
rates that are listed in Table 2-8. In addition to the con-
tinuous rate, which stores readings at the conversion rate
(about three readings per second), five additional inter-
vals from one reading per second to one reading per
hour are available. A special trigger mode allows you to
control the interval with the TRIG button. During the
rate selection process, the display will appear as fol-
lows:
r=3
In this example, the rate parameter is 3, indicating a 1
rdg/min interval.