Requirements

The system is designed to perform life tests of aerospace products hydraulic power steering, including drop tests. The measurement is performed on a pair of independent stands.

System records signals from up to 32 channels with sampling up to 2 kSa/s on each one. It is assumed to use all 32 channels for the strain gauge. There is also a reserve of some channels for measuring other signals, e.g., temperature or position (at the expense of strain gauge channels).

In addition, signals for a pair of load hydraulic motors are generated. The signal generating device provides feedback so that system makes corrections to the generated electrical signal according to the actual value of the load.

The system’s task is to generate load signals, monitor measured analog signals, and evaluate whether they meet the specified conditions. If so, they are forgotten in most cases. Otherwise, they are recorded on a large disc. The system considers the possibility of one site reconfiguring while measuring at the other one.

System description

Modules are placed in the VXI frame of the VX1410 type from Tektronix. The frame has 13 positions; 7 are occupied by measuring modules and a computer, so six remain available as a reserve for further system expansion. The frame is equipped with a fault monitoring module (e.g., drop-in power supply, overheating, etc.) that reports detected faults and the status of the air filter. The report is transmitted either via the RS232 serial line to one of the computers in the workplace or directly to the built-in measuring computer. This monitoring suits long-term unattended tests.

The frame is designed so that replacing the faulty module is as quick as possible in a failure. For example, replacing the power block takes three minutes. This feature minimizes the consequences of failure on long-term and unrepeatable measurements.

VX1410

DBS8700 module is used for the measurement. It has a 16-bit resolution at 200 kHz sampling. It contains logic to control coupled multiplexers (max. number of channels is 255). Assuming full-speed measurements on all 32 channels simultaneously allows sampling at up to 6,250 samples/s, meeting the measurement requirements with sufficient reserve. The module contains a pair of DMA channels designed for hardware data transfer via the VXI bus at full speed, without computer intervention. There is a possibility of independent sampling of individual channels. The module has built-in memory for the repeated sequence of channel sampling and amplification (scan list) consisting of up to 1024 steps. The module is equipped with a FIFO buffer for data with a depth of 1024 samples. Notably, the module allows the automatic start of the measuring sequence (without computer intervention) when the preset level on a given channel is exceeded. This feature can be advantageously used for automatic start of measurement only if the limit value of some signal is exceeded.

Input signals are multiplexed using a pair of 16-channel DBS8710 multiplexers. The multiplexers are equipped with sampling circuits on all input channels, allowing simultaneously voltage sampling at all inputs. It eliminates the problems arising from the gradual measurement of individual channels (the usual problem in many measuring tasks).

A pair of DBS8751 modules ensure the generation of motors. Each module contains four channels; each channel is equipped with a memory of up to 64,000 samples. Both writings from the computer and direct access to memory modules (DMA) change the memory contents. With the set sampling frequency, the data is transmitted by a D/A converter with the 16-bit resolution to the analog output, where a low-pass filter adjusts it with a cut-off frequency of 21 kHz.

PC-VXI module is a critical part of the system for test control, data evaluation, and generation of waveforms. A Pentium Pro 200 MHz is inserted into the VXI system frame, works in a Windows NT environment, and has 32 MB memory, an Ethernet port, PCMCIA, SCSI-2, and GPIB buses. It provides VXI bus control, allows block transfer of DMA speeds of up to 20 MB/s, and maps address spaces of VXI modules to their address space. Included is a VISA library with fully programmable trigger support and configuration programs. The module’s PCI/ISA expansion slot is equipped with an IRC position sensor board. The computer is very reliable.

VXI

The system is complemented by a custom-made measuring program created in the TestPoint development environment.

Program

This program provides measurement at two sites, evaluation and visualization of data, and control of excitation actuators. The control signal is force, but the system allows the regulation to a selected quantity level (i.e., even such that is calculated, not measured directly). The system is connected to the corporate LAN.

The system supports the generation of excitation curves. Due to its resistance to environmental influences and small dimensions, it is used to measure data in various modes of operation. The program then performs statistical processing of empirically determined values ​​and creates “typical” characteristics for the given mode of use. With the possibility of graphical modification of the excitation waveform and manual input of fault signals, modification of these characteristics is supported.

Program

The solution has the following main advantages:

  • a highly reliable solution,
  • the system grows very slow old,
  • delivery as a whole, warranty for the functionality of the system as a whole without the risk of undetected design errors,
  • one partner for solving possible complaints of technology and programs, domestic service,
  • an open solution allows combining the most suitable modules into one unit,
  • expandable to 128 channels,
  • up to 6,250 samples / s on all channels simultaneously,
  • feedback allows keeping the shape of excitation pulses not on the electrical output but directly as angle or displacement values, including the possibility to generate load signals of any course,
  • two channels of DMA (= hardware data transfer via VXI at full speed, no computer intervention),
  • possibility of independent sampling of individual channels,
  • built-in memory for repeating channel sampling and scan lists of up to 1024 steps,
  • FIFO data buffer,
  • automatic start of the measuring sequence (without computer intervention) when the set level on the channel is exceeded,
  • includes a dedicated three-channel IRC counter that counts back and forth with a zero mark,
  • one system for testing in the testing room and data acquisition from the operation,
  • connection to the environment via a computer network, data available anywhere in the company,
  • modules are VXIplug & play compatible, with full VXIplug & play support from National Instruments (i.e., de facto from the standard creator),
  • measuring program based on user requirements, developed with the participation of the user’s staff according to the mutually agreed project,
  • possibility of further modification of the program,
  • direct contact to program authors, hotline,
  • except for drivers, there is no customized code in any language (C, Pascal); everything is programmed in a graphical development environment instead,
  • detailed documentation,
  • possibility of lending modules during repair or calibration period,
  • all VXI modules are self-test equipped.

More information request here.