Tech Tip: Controlling Electronic Test Equipment with SCPI

The Circuit Specialists CSI3721A and CSI3723A programmable DC electronic loads and the 3631A, 3662A, 3663A, and the 3664A programmable power supplies are fully programmable test instruments that support the standard commands for programmable instruments (SCPI) control protocol. The SCPI standard specifies a common syntax, command structure, and data format for controlling and receiving data from a wide range of test and measurement equipment.


Array 3664A Programmable Power Supply

Because the communication type is not specified by the SCPI standard, you may use GPIB, USB, RS-232, Ethernet, and several other types of cables. Most of the Circuit Specialists units offers feature an RS-232 port, but they can also be used with USB adapters or outfitted with a GPIB interface as a special order.

SCPI commands are ASCII text strings consisting of one or more keywords and one or more optional parameters. Responses to commands such as data or handshake responses can be ASCII text strings or binary data.

SCPI commands either perform a “set”, such as turning a power supply or electronic load on or off, or a “query” operation, such as reading a voltage or current value. In addition to setting and querying in a single operation, SCPI enables you to group similar commands.

Examples of simple command syntax for performing an operation on an programmable electronic load like the CSI3721A are listed below.

INPUT OFF disconnects the load from the device under test.
MODE CCL sets the CC mode.
CURR:0.5 sets current level
INPUT ON connects the load to the device under test.
MEAS:CURR? sends the actual current measured back to the PC.

The SCPI specification provides an easy-to-understand and universal method for controlling and measuring a wide variety of electronic test equipment. Earlier protocols were mostly vendor specific and required a custom user interface to allow computer controlled operation. Circuit Specialists will be providing more test and measurement equipment that adheres to the SCPI protocol in the future as we improve and expand our selection of products.


George Leger has a Masters in Electrical Engineering from Stanford University, worked in private industry pioneering surface-mount technology and in government research labs for twenty years, published several papers on surface-mount technology, co-authored papers published in national symposiums on accelerator technology, was past president of SMTA and an adjunct professor at the community college level, holds a patent, and is a certified microchip design partner, serving as a consultant to many companies developing electronic circuits.

Leave a Reply