Project/RelayMatrix

Introduction

In professional test systems, there is often the need for switching. Power supplies, loads, and various measurement devices need to switch on or off, or be able to be chosen across multiple inputs or outputs on a test system. This is done by relays in most cases. Relays are fairly reliable, oppose little influence on the test system and have good conductivity in the "on" position, and also good isolation in the "off" position. As the complexity increases, the number of relays can also become very large. Purpose-built switching systems are efficient, but also less flexible. If you want maximum freedom, you will look for a system that can connect any input to any output. These kinds of systems have relays in a matrix configuration. For small signal types such as voltage measurements, a reed type relay is very compact, and a high density can be packed in a minimum of space. For switching larger currents, a more conventional type power relay is needed.

All of these relays must be switched at the right moment. Usually, there will be some sort of automated sequence system, controlling the progress of the task being performed. Scripting systems such as National Intrument's LabView or Keysight's VEE programs offer easy to understand graphical representation of a test sequence, with great flexibility. The test script systems communicates with equipment with a number of interfaces, varying from the ancient but still widely used IEEE488 parallel bus, to RS232, PCI variants, USB and Firewire busses and Ethernet connections. The common communication standard across all these interfaces is usually SCPI, the Standard Commands for Programmable Instruments. This is an human readable ASCII based set of commands, which is extensible and adaptable to a large number of instruments. Power supplies, vector analysers, multimeters and a host of other measuring and driving equipment can have SCPI support.

A relay matrix system is often an expensive piece of equipment, bound to a single vendor, and limited to a certain voltage or current. To find a suitable system, it can become neccesary to mix different types of relay matrix configurations. Because there of often the need for a compact system, small relays are used, which can be costly. Many thousands of dollars/euro's can be spent on a matrix system. But what if you could make a system yourself? Choose a cheap relay, buy them in bulk, and make your own system?