Model 2461 Interactive SourceMeter® Instrument Reference Manual
Section 2: General operation
2461-901-01 A/November 2015
2-115
Digitizing aperture and sample rate
In most cases, you will get good results if you leave the aperture at the default setting of automatic.
When auto is selected, the instrument makes as many measurements as possible in the sample
period. When it is set automatically, it is set to 1 megasample per second (rounded down to the
nearest integer).
You may want to set a manual aperture if you need an aperture that contains higher than one discrete
1
µ
s averaged reading.
Although the maximum sample rate is 1 million samples per second, the input filtering of the A/D is
set at a 3 dB corner point of slightly greater than 350 kHz to prevent aliasing. Therefore, a 350 kHz or
higher voltage input is attenuated by a factor of 0.707. For dynamic signals, this attenuation could
cause attenuated readings. Consult the specifications for detail.
Input frequencies above 500 kHz are occasionally prone to the signal processing problem of aliasing.
The following figure shows the relationship between the aperture, sample rate, and count.
Figure 74: Digitize aperture, sample rate, and count
For large count (more than 5,000,000) and sample rate values (more than 150,000), data may lost.
Adjust one of the values to a lower level.
Contact check
You can use the contact check function to prevent measurement errors caused by excessive
resistance in the force or sense leads. This can be caused by poor contact at the device under test
(DUT), failing relay contacts, or wires that are too long or thin.
Using SCPI or Test Script Processor (TSP
®
) commands over a remote interface, you can check for
excess resistance in the connections from the front and rear panels of the Model 2461 to the DUT.