The concept of using modular instrumentation at the heart of functional ATE systems was quickly established following the introduction of the VXI platform in 1987. Back then, defining a system interface was a simple matter of selecting your preferred interconnect receiver and connecting the instruments to it with cables. Aside from the inevitable noise and crosstalk issues always associated with cable harnesses, this process worked well.
Twenty six years on and the PXI platform, not VXI, is now at the forefront of new ATE designs. PXI offers unparalleled performance and density in a much smaller footprint and traditional cabling methods to the interface simply don't meet the requirements of these modern ATE systems.
As a designer and manufacturer of system interconnection solutions, MAC Panel sought to develop a PXI interconnection that eliminated the cable harness between the PXI instruments and the ATE interface. The result of this development was the SCOUT interface.
In place of cables, the SCOUT receiver utilises connection assemblies that incorporate a pcb to connect between the PXI instrument and the receiver connector. The connection assembly, known as a DAK (Direct Access Kit), is attached to the front face of the PXI instrument to form a single PXI/DAK assembly. A DAK is attached to each PXI instrument in the ATE system.
Installation of the PXI/DAK assemblies involves simply inserting the PXI/DAK through the SCOUT receiver and screwing the DAK in place; a couple of minutes per instrument. The SCOUT receiver is designed to provide precise alignment to the PXI chassis (see fig 1).
All DAK pcb designs incorporate extensive shielding to eliminate noise related issues that might negatively impact signal performance and integrity. Additionally, the pcb's are housed in an aluminium casing offering additional noise protection.
By using a pcb interconnection it is possible for users to incorporate customer circuitry into the DAK. This is typically application specific such as signal conditioning, lvds circuitry, isolation and boundary scan hardware etc. In fact both Goepel Electronics and JTAG Technologies have released a DAK version of their popular PXI boundary scan hardware. There are already many examples of how a DAK can be customised to suit specific application requirements.
Some PXI instruments are unsuitable for pcb connection due to signal types. High power switching or rf signals for example. In such cases, short wires (180mm) are utilised in place of a pcb. Again, this offers significant performance advantage over typical cable methods where the cable is usually a minimum of 500mm long.
Many ATE systems are a hybrid design using PXI in conjunction with other instruments. The SCOUT receiver is designed to incorporate cabling for other instrument sources which can easily connect to spare connector slots on the SCOUT receiver. Where there is a considerable amount of non-PXI I/O requirements; there is a SCOUT receiver available specifically designed to accommodate this requirement.
There is a variety of SCOUT receiver designs available to suit the many makes and models of PXI chassis' available, as well as more than 600 COTS DAK designs. The defence and aerospace market has largely adopted PXI as its preferred ATE instrument platform. By their nature, some defence ATE's have a large number of instruments; requiring more than one PXI chassis. SCOUT is now available for a dual chassis configuration; connecting two PXI chassis' simultaneously.
In summary, SCOUT eliminates PXI system cable harnesses, offers superior signal performance and stability, reduces system build times and reduces short and long term system costs.
Gary Clayton is sales director for MAC Panel.