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SVM2608 Introduction 11
SECTION 1
INTRODUCTION
INTRODUCTION
The SVM Series leverages off VXI Technology’s line of high-density modular VXIbus
instruments, but are optimized for the VMEbus. All SVM instruments are designed to provide all
the features of test instrumentation in other platforms such as GPIB or VXI. These features are
achieved in hardware rather than in a driver. This approach to the interface design guarantees the
user that all communications to the module occur in microseconds, as opposed to several
milliseconds, considerably improving system throughput. The board is equipped with a
microprocessor which significantly increases the module’s functionality and task performing
capabilities.
The SVM2608 is a ruggedized circuit card designed for insertion into a convection-cooled VME
chassis. It is a double height VME size module (6U) of single slot width and conforms to all
physical requirements as specified by VME specifications. The VME interface is compatible with
the VME32/64x configuration with two 160-pin (32 x 5) backplane connectors (P0 – P1). The
SVM2608 consists of four low-speed (100 kSamples/s) channels and, with the addition of the -01
Option, can include two, high-speed (20 MHz) channels.
OVERVIEW
The SVM2608 is a precision, four channel digitizer capable of capturing data on all four channels
simultaneously either in FIFO (or “real-time”) mode or Linear (or “burst”) mode. A processor
enables the user to perform a variety of calculations with the data acquired. Each channel is also
capable of measuring voltage and resistance. All four channels can measure voltage at the same
time, but resistance can only be measured one channel at a time. Resistance can be measured in
two different modes: 2-wire or 4-wire. Both modes use a local current source to inject a current
into the resistor under test and then measure voltage across the resistor.
All four channels are independent of one another. The front end of each channel has both a
variable gain amplifier and an attenuator, thus allowing for full ADC scale measurements of
signals from 1 V to 100 V. Before being digitized, the signal can be passed through a Low Pass
Filter (LFP) with a cut-off frequency of 20 kHz. The ADC is a 16-bit converter capable of taking
as many as 100 kSamples/s on a scale of -10 V to +10 V. To compensate for offset and gain
variation in the ADCs, each channel has two 12-bit DACs that are used to calibrate the offset and
the gain on each channel ADC. These calibrations are performed at the factory using precision
voltage reference sources.