Semiconductor Laboratory

Computer supported measurement techniques

Computers are often used to communicate with measurement equipment to automate a measurement. There are many ways to implement this communication. While it is possible to commuicate via the serial ports or UBS ports using a low-level computer language, it is usually more convenient to use a high level language such as LabVIEW or Python to communicate with instruments. These languages can then also be used to manipulate the data and display it.

Some instruments implement the Virtual Instrument Software Architecture (VISA). This is a standard that gives the instruments plug-and-play capability. Programs that understand VISA (like LabVIEW or Python) can recognise which instruments are connected to the computer and communicate with them. Usually this communication takes place by sending text strings to the instrument. A common format is called Standard Commands for Programmable Instruments (SCPI). Some manufacturers do not follow these standards and it is necessary to install drivers to communicate with their instruments.

For instruments that have a microprocessor and memory, it is often possible to upload a program to the instrument and then tell the instrument to execute this program. Suppose you want to measure a voltage as a function of time. If you repeatedly send a command to read a voltage, there will be a delay between every measurement due to the communication between the computer and the instrument. However if you first upload a program to the instrument that instructs it to rapidly make 10000 voltage measurements and store the results in local memory, the measurements can be made more closely spaced in time.