Series 7000 Ruggedized Ethernet Data Acquisition Systems
Fully self-contained, the 7000 provides transducer excitation, bridge completion and balance. The transducer output is amplified, filtered to remove signal components that could produce alias errors and digitized to 24-bit resolution. The digitized transducer output is digitally processed providing multiple sample rates, an 80 dB/octave FIR filter and 32-bit floating point output format in millivolts referred to input, millivolts referred to output or user defined engineering units.
Three models are available that differ in their excitation and signal conditioning capabilities. Model 7X16 for strain gage and bridge transducers has programmable voltage excitation, bridge completion for 120 and 350 Ohm strain gages, shunt calibration and automatic balance. Model 7X20 is similar but provides regulated power for transducers with internal electronics. Model 7X18 is for voltage inputs. The amplified transducer signals are digitized, processed and output at 10 to 24,000 samples per second (Model 7200), 102,400 samples per second (Model 7300) or 204,800 samples per second (Model 7400) as selected for individual channels. A digital signal processor (DSP) provides low-pass filtering selectable from 10 Hz to 3,000 Hz with 80 db/octave roll-off.
Each module has a 100BaseT Ethernet interface for control and data output, which simplifies system wiring and provides remote and distributed operation. IRIG time may be employed to synchronize sampling on multiple modules within 10 microseconds, or a TTL timing may be used to achieve better than 1 microsecond time alignment. Multiple modules with up to 4,096 channels may be connected on a single Ethernet LAN.
The module enclosure features interchangeable end plates that provide fully sealed, ambient air or forced air cooling. Forced air cooling provides the capability to operate over a wide temperature range according to application requirements. Occupying less than 500 cubic inches and weighing less than 14 pounds, the 7000 systems can be installed in locations previously not suitable for data acquisition systems. The Ethernet interface and IRIG timing make it easy to distribute enclosures throughout the test facility, minimizing sensor cabling and installation costs.
The Series 7000 does not sacrifice performance for size or portability; it features higher accuracy than most systems designed for a laboratory environment. For the 7X16, accuracy is better than 0.025% for gains up to 200 and 0.05% for gains above 200 over the temperature range -20°C to +50°C, which can be extended to higher temperatures by forced air cooling.
Series 7000 is supported by Pacific’s PI770 software that provides a ready-to-run application and an SDK for user program development. Calibration and performance verification is accomplished by PANEL72 Maintenance and Calibration software. The ACS2000 Automatic Calibration System automates performance verification and periodic instrument calibration.
Series 7000 Functional Block Diagram
|Cabling transducers to a remote data acquisition system is costly and may require intermediate signal connections that introduce reliability problems. In addition the transducer and cable impedance can filter the signal, attenuating high frequency signal components. Locating data acquisition hardware near transducers at many test facilities has required specially constructed and environmentally conditioned enclosures. Using the Series 7000, the data acquisition can be installed in unprepared locations and the only external connections are power, timing and Ethernet.
Model 7X16 maintains ±0.025% uncertainty (±0.05% for gains above 200) over the full temperature range by continuously correcting for temperature induced excitation, gain and zero variations. Models 7X18 and 7X20 maintain better than ±0.05% uncertainty for gains up to 200 and ±0.1% (for gains above 200). The 7200 modules are calibrated and correction vectors are stored in non-volatile memory. An internal sensor determines the correction vectors applied to the data according to the device temperature. Software is available for automatic recalibration. An internal programmable voltage reference that can be externally monitored is provided to verify channel performance.
The excitation output is programmable from 0 to 15 Volts with better than 1 millivolt resolution. Calibrated 1 Volt ±0.1% steps are also provided. Output current is 50 mA. The excitation voltage is continuously monitored by sense inputs connected to the sensor and automatically adjusts as necessary to maintain a constant voltage over the full temperature range. Bridge completion is programmable for quarter-bridge, 120 and 350 Ohm gages, half and full bridges. Other values can be supplied on request. Two steps of shunt calibration are provided. Transducer balance employs a high-resolution DAC and is initiated by program instruction.
The sensor inputs are protected up to ±50 Volts differential and ±30 Volts common mode. They are applied to a high impedance, programmable gain, differential instrumentation amplifier. The amplifier has programmable gains from 1 to 1,000 providing full-scale input ranges of ±10 mV to ±10 Volts. Calibrated gain steps with ±0.02% accuracy are provided or the amplifier gain may be continuously programmed. Autozero maintains the amplifier output offset within ±1 mV.
Analog to Digital
Conditioned and amplified transducer signals are digitized by a 24-bit resolution Sigma-Delta analog-to-digital converter that over-samples the analog signal enabling the use of a single frequency anti-aliasing filter.
Sampling is synchronized between channels and systems providing time aligned data. All channels are simultaneously sampled at the highest sample rate, 24 kS/s. The sample clock may be synchronized to IRIG A, B or G time. IRIG G time is generated by the unit connected to the external IRIG source or designated as the master time source if external IRIG is not used. Distributed to multiple system it maintains channel to channel time skew less than 1 microsecond for channels in the same or other systems using the same master time source. If the timing signal is not present or lost during acquisition sampling will continue at the last programmed rate using an internal clock.
Finite Impulse Response (FIR) filtering is provided. Eighty sets of 128 FIR filter coefficients are available in each 7000, providing an extensive selection of filter frequencies and characteristics. The coefficients are user programmable, and each coefficient is 18 bits in length. The filters are loaded with customer-specified default coefficients providing logical filter cutoff selections and characteristics. The default filter frequencies and characteristics are easily changed using program instructions to satisfy future requirements.
Data are output in a digital format on the Ethernet interface. The output data is 32-bit floating point format and can be chosen via programming to be Volts, millivolts, microvolts, or user defined engineering units derived from a polynomial expression. Each system can output data from all channels at the maximum sample rate. Data rates in excess of 7 million samples per second are achievable from combined systems on a single LAN.
All operating parameters can be set and queried using the extensive, built-in command set. Setup information is saved in password protected EEPROM memory on board, and it is automatically restored when power is applied or the system reset. The command set is well documented, and source code programming examples are provided.
PI770 is the choice for test management, data acquisition, and data display. Ready to run out of the box it is a 32-bit application that runs on Microsoft Windows operating system. It provides all the tools for test definition, setup and tracking, transducer calibration, data acquisition, display, replay and export, and test quality validation. PI770 comes with an Application Programmer’s Interface that greatly reduces the development time for custom operating software. PANEL72 is Pacific’s maintenance and calibration software. It may be used to troubleshoot installation problems and calibrate the 7000 modules.
Initializing communication with the Series 7000 is simple. Commands are included that enumerate the 7000 devices on the network. After the enumeration operating software creates a socket interface between itself and each 7000, simple Send and Receive network commands are used to communicate. Status LEDs that assist with initial setup are located on the connector end of the enclosure. Multiple systems, up to 4,096 channels, may be connected to a single Ethernet LAN.