RTC Magazine

Providing high voltage that can be remotely controlled in a small, confined area is a problem faced by many laboratories around the world. This problem became apparent for Sandia National Laboratories (SNL) when working with the world’s most powerful X-ray generator named the Z-Machine. The Z-Machine is capable of releasing 290 trillion watts for a billionth of a second. That’s 80 times the world’s electrical power usage. Due to the nature of these large scientific machines, the systems need to be placed behind Faraday shield screen boxes inside the Z-machine. And because of the limited space, Sandia needed a power solution that could stack 20 channels of high-voltage power in an area no larger than 19” x 40” x 20” and be controlled and monitored remotely via computer control.

Physics experiments often require many (up to 1000) continuously variable high-voltage (2kV to 6kV), low-current power supplies for various types of experimental apparatus, such as photo multipliers, ion chambers, tracking chambers, etc. In the past, this has often required a variety of units from different manufacturers with different voltage-current ratings, control interfaces, voltage, current and state monitoring circuitry and output protection features.

The physical packaging and I/O connections were also dissimilar. Such lack of uniformity has caused problems with system implementation, maintainability and control/monitor software because of the need to custom-tailor for each type. The work required to implement large, multi-channel high voltage systems with these system was often difficult and expensive.

Traditional high-voltage power systems were offered in NIM, VME or CAMAC architecture. Implementing a full 64-bit bus in VME requires a 6U form-factor, where in CompactPCI, both 32-bit and 64-bit can be implemented using a 3U form-factor. Unlike the older VME-based high-voltage power systems, where the main electronic design constraint was cost, newer designs must meet additional requirements for size, power consumption, remote control and monitoring capability. Newer designs should also be able to seamlessly integrate with other manufacturers off-the-shelf products in an environment containing a large variety of electronic equipment.

The CompactPCI architecture allows easy integration of needed functionalities into a single system. Instrumentation, data acquisition, machine vision, motion control and bus interface modules are just a few types of CompactPCI modules available. It also provides a high-performance and rugged industrial form-factor along with high compute density and higher-quality components. Taking these points into consideration, the CompactPCI architecture has been found to meet Sandia’s high-voltage system requirements.

Major system requirements are as follows:

1) DC supplies should be modular with the modules supplying an array of voltage ranges (typically -100V to -5KV)

2) Current draw in a quiescent state should be very small (typically < 1 mA)

3) Individual modules should be stable to 5% of the set value over a period of time

4) The ability to control and monitor the voltage and current characteristics remotely using a computer

5) Small and robust design, which is easy to maintain

6) Scalable in nature

System Architecture

Bi Ra Systems has three versions of these high-voltage module boards. Model 4720 has four high-voltage channels each having a voltage range from 0 to -300 volts; Model 4720A (Figure 2) has three channels with each channel having a range of 0 to -300 volts and Model 4730 has two channels, each having a range of 0 to -5KV. Since robustness and remote control and monitoring of these high-voltage systems were a priority, the next consideration was the selection of an appropriate, modular computer-interface bus system.

Once again CompactPCI proved to be the bus backplane of choice. The chassis selected for this purpose is National Instruments PXI-1044, which accepts both PXI and CompactPCI 3U modules. The PXI-1044 offers 467W of available power across 14 slots with 25W of cooling for each slot provided by three fans running at 140 cfm. The chassis is PXI specification Revision 2.1-compliant. It is equipped with NI-8196, which is a high-performance Pentium M 760-based embedded controller for use in PXI and CompactPCI systems. The PXI-8196 includes high-performance peripheral I/O such as 10/100/1000 Base TX Ethernet, four USB ports, an RS-232 Port and an IEEE 1284 ECP/EPP parallel port. This allows the user to have a choice in selecting the peripheral for remote communications with the chassis. Additionally, it comes with 512 Mbyte dual-channel DDR2 RAM and Windows XP Professional already installed.