Suppress; Zero Checkand Correct - Keithley 595 Instruction Manual

OPERATION
I
RELEASE
INTEGRA'TOR
INTEGRATOR
OISCHARGE
cx -sg" o/t-y
CX( CCIRRECTED I - cx -
(O/t)(DELAY TIME+t,)
STEPV
READING VOLTAGE=V+ISTEPV
1 z ~-~~-
When the SW~RJZ$S button is pressed, ~JI: instrument
&ill store the next mea&rement as a baseline. The SUP-
PRESS indicator light will illuminate. Au subsequent
readings taken will be the difference between the measured
value and the stored baseline.
The baseline maintains its absolute value regardless of
range. For example, if a O.lnF
signal
is suppressed on the
2nF range, it will remain at O.lnF on the 2OnF and 2OOpF
ranges. Only one reading for the presently selected func-
tion can be suppressed; the value will be lost if the func-
tion is changed. The instrument can be toggled between
Q/t and capacitance without losing the stored value.
The suppressed readings can be as small as the resolution
of the instrument will allow, or as large as full range (see
Note 1). Some typical examples indude:
Applied Suppressed
~~ -.~Signal Reading
Displayed
Valila
Figure 3-3. Integrator Charge vs Time Curve for a
30
pF 0.5 pF
29.5
pF
Capacitance Measurement
- 1.5 IIA
-1 l-IA - 0.5 nA
11.3 nF l3nF
- 1.7 Is
3.3.3
C/Co-STORE Co
C/Co allows the user to normalize capacitance to a stored
capacitance value (Co). c/c, applies only to the capacitance
reading (even while Qk is being displayed). To store a
capacitance reading (Co), simply set up- the desired
capacitance measurement, then press SHIFT then STORE
&. The next reading will be stored as Co. To normalize
the capacitance readings to Co, prks C/Co (the LED will
come on). This will divide a!J subsequent readings by the
stored reading, Co, and show the resulting quotient on the
display. Once a value of Co is stored, it will be retained
in memory until a new value is stored or the instrument
is turned off.
O.lOpA - O.OlpA
OSlpA
NOTES:
1. Using suppress reduces the dynamic range of the
measurement. For example, if the suppressed value is
lOO.OOpA on the 2OOpA range, an input current of more
than 99.99pA would overrange the instrument even
though input currents up to 199.99pA are normally
within the capabilities of the 2COpA range.
2. Setting the range lower than the suppressed value will
overrange the display; the instrument will display the
"OL" message under these conditions.
3. To store a new baseline, suppress mu&first be disabled
and then enabled once a&n. The next reading taken
will be stored as the n&baseline.
C/Co allows comparison of the relative shapes of two or
4.
more CV curves even when absolute capacitance values
Enable suppress on the measurement range that yields
the highest resolution for the application.
may be different.
5.
If the ins&ument is displaying Q/t when suppress is
enabled, the capacitance value will be suppressed even
3.3.4 SUPPRESS
though the caiacitance reading is not dkslayed. Sup-
pression has no effect on Q/t readings.
The SUPPRESS button allows the user to compensate for
external offsets present in the test setup by subtracting the 3.3.5 ZERO CHECK and CORRect
offset value from subsequent readings. (To compensate for
internal offsets, see~ZER0 CHECK and CORRect.) Sup-~- zero che& is -d to protect the input amplier of the
Press~maY be used with capacitance or went measure-
men& but not Q/t.
~Model595 from overloads and switch@g transients when
changing instrument functions or connections to the devices
3-3