VDSP-431 system & functional block diagrams
(this page is under construction. 2-14-2002)

The VDSP431 Digital Servo Controller  is a set of two different type of modules that when connected together provide a complete intelligent system able to control up to 6 channels of  double load cell . Up to (4) sets of VDSP-431 can be combined with (12) VDSP-SCM module to make a a 24 channel, DUAL feedback  (AC & DC) digital servo control systems as pictured above in photo 1.

This module is an intelligent DSP base VME module . It can support up to 3 VDSP_SCM
module. The primary features of the VDSP431M are as follows:

This module is a slave carrier board populated with 2 double load cell signal conditioning.
Signals conditioning are : The VDSP-SCM module is a servant carrier that is populated with :

A/C Singnal conditioning:

The A/C module is designed around the AD698 LVDT signal conditioner from Analog Devices.  The excitation frequency can be set between 20 Hz and 20 KHz by changing capacitors.  The VDSP431 AC Module is preset to 10 KHz at the factory.  The output of the LVDT demodulator is amplified by the same circuitry utilized by the DC Module.  Programmable relays allow the LVDT demodulator to be bypassed.  This is so the AC Module can be used to support DC high-level inputs such as a DCDT.  The AC excitation can be disabled when DC high-level mode is used.  Two  fourth order filters, with a cut-off frequency of 500 HZ, remove any residual carrier signal from the demodulator output. The LVDT modules excitation is preset at the factory to 7.0 Vpp at 10.0 KHZ. The demodulator gain is set to output +/- 9 Vdc over full stroke of the LVDT.

D/C Signal conditioning:

Incoming low level LoadCell signals are amplified by  high precision low noise, low offset, high impedance instrumentation amplifier. The SCM PGA Modules utilize a two stage instrumentation amplifier design that is able to provide any gain between 1 and 5000.

The PGA module containes a differential voltage power amplifier that is controlled digitally by a 16-bit D/A.  The output voltage is proportional to the D/A  output voltage. A +5v D/A output is translated in a 10 V peak-peak excitation voltage. The maximum output is 18v peak to peak into a 100? load.  Remote sense lines can be incorporated to compensate for voltage drops due to long wire lengths.

Valve driver:

The Valve driver module is able to drive up to 100 ma into a  200 ohm load.  The output of a 16-bit D/A converter drives  two power amplifiers that convert the input voltage signal to a current signal.  Output of the current is directly proportional to the input signal.  The current range is programmable by software using relays.
Four ranges are available :

Current selected is calculated with an input voltage of 5 V.Overdrive can be up to 100 %. The actual current delivered to the valve can be monitored by the DSP.  A differential amplifier converts the output current to a voltage signal directly proportional to the current flow into the load.

Load Cell configuration:


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1898 E. SOuthern Ave
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