Signal
Conditioner/Amplifier
8000
Description
R.C. Electronics Inc. advances the state of the art in signal
conditioning with the Model 8000 Computer Controlled Signal
Conditioner and Amplifier. The Model 8000 combines the high
precision and proven reliability of manually controlled amplifiers
with the speed, convenience and accuracy of operation resulting
from computer control.
The 8000 offers the operator many advantages, including the
ability to quickly and accurately set gain offset, filter cutoff
and excitation voltage from a local or host computer. Settings
may be made either individually via the computer keyboard or
a complete test setup of all amplifiers may be made in seconds
using data stored in the host computer memory.
In addition, all these parameters can be read back from
the 8000 by the host computer to display overall status or provide
a permanent printed record. The 8000 also has a status output
that, upon interrogation, allows the user to record all settings
over the Tape or Galvo output in a PCM coded format.
Interfacing to the host computer is provided by an RS-232C
or IEEE-488 bus. An optional portable computer can be used
to provide
local control via a second dedicated RS-232C port.
The Model 8000 consists of a main frame and a plug-in Bridge
Completion Module. The main frame provides the isolated power
for the excitation supply and a high precision differential
DC amplifier. The Bridge Completion Module allows the user
to
handle all types of resistance transducers including strain
gauges, RTDs and potentiometers. Each conditioner is fully
guarded
and isolated as required to maintain signal integrity. System
hardware consists of three major components: Model 8000 Signal
Conditioner/Amplifiers, a Master Rack and a Slave Rack.
The Master Rack houses the initial group of eight Model 8000s
with a Slave Rack for each additional group of eight. Slave
Racks can be accommodated to allow system expansion to as
many
as 2048 Model 8000 units. The Master Rack contains the master
microprocessor which communicates with the host computer,
the
portable local computer and the microprocessor in other Slave
Racks. The master microprocessor speaks to all slaves by
a round
robin serial link, allowing complete data verification between
all groups of 8000s.
Each Model 8000 is controlled directly by the microprocessor
in its Master or Slave Rack.
The 8000’s precision differential DC amplifier features
multiple feedback techniques to reject common mode signals.
Input impedance is greater than 50 megohms. Bandwidth is 500
kHz. The power supply’s triple-shielded power transformer
provides maximum isolation for transducer excitation.
Design Features
A versatile plug-in card is provided with the Model 8000 allowing
the user to complete two independent bridges via an 8-pole
DIP switch. This is an easy means of switching between two
bridges of different resistance (e.g. 120 Ohm and 350 Ohm).
In addition to bridge completion, there are provisions on the
plug-in card for mounting up to 16 Shunt Calibration resistors.
This will support up to ±4 steps of single or double
Shunt Calibration. Four resistors are selectable per step
of
single shunt calibration or two resistors per step of double-shunt
calibration.
All transducer input wires (up to 10 conductors plus a shield)
are routed through the Bridge Completion card. Included on
the
card are provisions for the addition of components (resistors
and capacitors) for customizing the Model 8000 to suit a wide
range of applications. These include but are not limited to
the following functions: 1) AC coupling in input signal; 2)
Custom voltage dividers for voltage substitution calibration;
3) Versatile bridge completion/shunt calibration.
Automatic Bridge Balance
The Model 8000 offers an extremely convenient and accurate means
for automatically balancing the input bridge circuit. The optional
“Auto-Zero” circuit senses the polarity of the amplifier
output and injects an isolated ratiometric correction voltage
into the amplifier’s input to effectively null out any
zero offset that may be generated by the bridge circuit. The
auto-zero function is activated by a computer command. A front
panel LED is illuminated while the auto-zero sequence is in
progress.
Two ranges of Auto-Zero Adjustment are provided in both a Ratiometric
and Zero Suppression Mode. In the Zero Suppression mode the
computer has full control of the voltage insertion circuit
in steps of 40 mV RTI or 1.8 mV RTI allowing the amplifiers’
output to be set anywhere from minus to plus full scale.
Filter
The 8000 features provisions for mounting up to 6 plug-in filters
in any configuration of 2, 4 or 6 poles using Bessel or Butterworth
characteristics. Cutoff frequencies range from 1 Hz to 100 kHz.
Each filter is coded with an 8-bit identifying number, which
is read and stored by the computer to assure data validity.
Filters can be independently selected by the computer to provide
either the same or different cutoff frequencies for the tape
and galvo output.
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