Keithley KUSB-3100, User Manual

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Principles of Operation
15
2
2
2
2
2
2
2
2
2
Vin = Code
Offset Binary
* LSB + Offset
where,
• FSR is the full-scale range (20 V).
• N is the input resolution (12 bits).
• LSB is the least significant bit (0.0048828 V).
• Vin is the analog voltage.
• Code
Twos Complement
is the raw count used by the software to
represent the voltage in twos complement notation.
• Offset is the actual minus full-scale value ( – 10 V).
• Code
OffsetBinary
is the raw count used by the software to represent
the voltage in offset binary notation.
For example, assume that the software returns a code of 3072 for the
analog input value. Determine the analog input voltage as follows:
Code
Offset Binary
= Code
Twos Complement
XOR 2
N-1
Code
Offset Binary
= 3072 XOR 2048 = 1024
Vin = 1024 * 0.0048828 V + – 10 V
Vin = – 5.00 V
Error Conditions
An overrun condition is reported if the A/D sample clock rate is too
fast. This error is reported if a new A/D sample clock pulse occurs
while the ADC is busy performing a conversion from the previous
A/D sample clock pulse. It is up to the host application to handle this
error either by ignoring the error or stopping acquisition. To avoid
this error, use a slower sampling rate.