Keithley 6487 User Manual

Model 6485 and 6487 User’s Manual Buffer and Sweeps 6-3
Buffer timestamp
To change the buffer timestamp format, press MENU, select TSTAMP, then press ENTER.
Select the desired option: ABS (absolute) or DELT (delta). For ABS, each timestamp is ref-
erenced to the first reading stored in the buffer. The first reading always has a timestamp of
0000000.0000. With DELT, each timestamp provides the time between the readings.
Clear
To clear the Model 6487 buffer, press CONFIG followed by STORE, then set the reading
count to 0 (pressing AUTO will clear the display quickly). Press ENTER with a reading
count of 0 displayed to finish clearing the buffer.
Buffer statistics
• MIN and MAX provides the minimum and maximum readings stored in the
buffer. It also indicates the buffer location of these readings.
• The PK
-PK (peak-to-peak) value is the difference between the maximum and
minimum readings stored in the buffer:
PK-PK = MAX - MIN
• Average is
the mean of the buffer readings. Mean is calculated as follows:
y
n
Σ
X
i
n
-----
i=1
=
Where: X
i
is a stored reading.
n is the number of stored readings.
• The STD
DEV value is the standard deviation of the buffered readings. Standard
deviation is calculated as follows:
y
n
Σ
Avg X
i
–()
2
i1=
n1–
------------------------------------=
Where: X
i
is a stored reading.
n is the nu
mber of stored readings.
Avg is
the mean of the buffer readings.

Keithley 6487 Specifications

General

Type	Picoammeter/Voltage Source
Current Measurement Range	20 fA to 20 mA
Interfaces	GPIB, RS-232
Voltage Burden	< 200 µV
Input Impedance	>10^14 Ω
Power	100 V / 120 V / 220 V / 240 V
Basic Current Measurement Accuracy	0.4%