Programmable Signal Conditioning                  DTX 5000 Series 



The DTX-5000 Signal Conditioner Series provides up to 64 channels of state-of-the-art signal processing in a compact (5U) chassis. Using hybrid mixed-signal technology, high-performance analog circuitry is combined with Digital Signal Processing to give gain accuracy performance previously available only in larger customized modules. A simple-to-use graphical user interface running under the Windows 2000 operating system allows for ease of setup and either local or remote operation as a network-based instrument node. The suite of conditioner modules include a strain amplifier with internal bridge completion, a general-purpose instrumentation amplifier with selectable AC or DC coupling, a linearized thermocouple amplifier with cold-junction compensation, a frequency-to-voltage converter with dual inputs for direction sensing, and an ICP accelerometer amplifier with constant-current excitation.

Design Features

Modular design using separate fully shielded four-channel modules with isolated power supplies reduces noise and allows for interchange of module types within a single chassis. During system design, special attention was given to reducing noise and improving reliability. All signal input and output connections are made directly from the external connector to the module backplane, and from there directly to the module. This eliminates long input cables and additional interface connectors that can pick up noise or become intermittent. The 6-layer backplane board includes large areas of ground plane to reduce noise pickup. Isolated power supplies are included on each module to separate the signal grounds from the digital ground. And all the module electronics are housed in rugged, shielded enclosures. Good temperature stability is obtained by doing the majority of signal processing in the digital realm, where temperature drift has no effect. In the analog circuitry that does exist, premium stability components are used to keep gain or offset drift to a minimum.

COTS Technology

Using commercial-off-the-shelf (COTS) computer hardware (Pentium processor) and a standard operating system ensures compatibility with future technology trends and facilitates product maintenance. A standard 10/100 base-T Ethernet interface is provided for network-based operation, and PC-compatible keyboard, monitor and mouse ports are available for standalone operation.

Mixed Signal Technology

The actual circuitry inside each module type varies, but they all share a common design approach. The input signal is first amplified to a usable level, and is then converted to a digital signal using a high-speed 16-bit Analog-to-Digital converter. This allows all gain correction and filtering to be done digitally, thereby improving system accuracy and stability. A Digital Signal Processor (one for each channel) uses stored offset and gain calibration factors to correct the digitized data values, and performs the requested low-pass filtering. The DSP also compares the signal level to user-specified limits, and sets the color and brightness of the front-panel Signal LED accordingly. After signal processing has been completed, the digital value is converted back to an analog voltage by a high-speed 16-bit Digital-to-Analog Converter. A four-pole low-pass filter removes the digitizing steps in the reconstructed signal, along with any high-frequency noise, and an output buffer provides up to 50 mA of signal current to the output load.

Sensor Power/Excitation

Each module also includes separate programmable Excitation Voltage generator for each channel (Excitation Current in the case of the ICP accelerometer conditioner). A power buffer is used to provide up to 100 mA of load current, and a sense circuit monitors and corrects the excitation voltage (or current) value in real time to compensate for fluctuating load conditions. Good temperature stability is obtained by doing the majority of signal processing in the digital realm, where temperature drift has no effect. In the analog circuitry that does exist, premium stability components are used to keep gain or offset drift to a minimum.

Module Calibration

High accuracy is obtained in the 5000 Signal Conditioners by implementing a unique end-to-end calibration scheme. A precision programmable voltage generator is connected to the input of each channel, and two calibration voltages (0V and approximately 80% of full-scale input) are applied during system calibration. These voltages are amplified by the input stage, converted by the A/D, processed by the DSP, converted back to analog by the D/A, filtered by the output filter, and then measured by a high-accuracy 24-bit A/D converter. The input and output voltages are compared, and system gain and offset correction values are computed and saved in the DSP memory. When data is being collected, these correction factors are applied to each data point in real time, resulting in a system accuracy better than ±0.05% of full-scale.

Front Panel Display

Careful attention was given to providing a meaningful front panel display of signal level and system status that wasn’t confusing to the operator. With 64 channels being displayed simultaneously, it can be easy to miss a channel error in a field of flickering lights. The 5000 Signal Conditioner uses just two LEDs per channel to display a variety of status conditions and signal levels. Various normal functions are indicated by varying the flashing rate or intensity of green LEDs. But system errors or signal overloads are immediately flagged by changing the appropriate LED color to red, causing that channel to instantly stand out from the rest.

Graphical User Interface

The control software display includes a summary view of the status of all 64 channels, essentially a copy of the chassis front panel, a spreadsheet view of the parameter settings for each module, and a detailed block-diagram view of the settings for each channel. Two dedicated LEDs per channel give instant feedback of channel status and signal level, warning the user of overload or other potential error conditions.
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Last Updated: 31-Jul-2012  

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