Industrial and Scientific Computing, Validation and Automation
LabVIEW, TestStand, LabWindows/CVI

Test bench and Measurement freelance Engineer

SCPI (Standard Commands for Programmable Instruments) is a standard that defines a language for communicating with instruments based on messages. The majority of the GPIB instruments use the SCPI but also RS-232, Ethernet, VXI, PXI may use it. Several measurement instrument manufacturers have adopted this standard as HP / Agilent for example, allowing some communication uniformity between several devices.

Some examples of SCPI commands:

Instrument identification querry: *IDN? Instrument reset: RST Measure querry: MES?

IVI (Interchangeable Virtual Instrumentation) is a specification of instrument driver published by the IVI Foundation, formed by the biggest names in the instrumentation as Agilent, National Instruments, Rohde & Schwarz, Aeroflex, Tektronix, Teradyne, Pickering and other.

This specification defined instument classes (multimeter, oscilloscope, power supply, ...). All drivers in the same class have the same exported functions. This ensures instruments compatibility and interchangeability: measurement software is linked to the driver class that needle to the specific driver of the used instrument.

Example: I have a test application which measures voltage with a multimeter. My software calls the driver of the multimeter class. IVI refers to the specific driver for the X model from Agilent. Thus, we can change this multimeter by the Y model from Agilent or the Z model from Tektronix  with a simple configuration without modifying the software (for since we have installed the IVI driver of these three instruments).

List of instrument classes defined by IVI:

Digital multimeter (DMM) Oscilloscope Arbitrary waveform/function generator DC power supply AC power supply Switch Power meter Spectrum analyzer RF signal generator Upconverter Downconverter Digitizer Counter/timer Some specific instruments do not fall into this classification. In this case it is possible to create a new class.

LabWindows/CVI provides wizards for developing drivers and adding a new class.

IVI driver scan be called by any type of programming language. However TestStand, LabVIEW, and Measurement Studio can offer all the key functions in hand for their use.

GPIB or IEEE 488 is the specification that defines a parallel bus of digital communication over short distances. It is widely used in industry or scientific research to test applications and able to control instruments (multimeters, oscilloscopes, spectrographs, power ...).