Manual

3-22 BHK-1/2-MG 121313
3.6 PROGRAMMING TECHNIQUES TO OPTIMIZE PERFORMANCE
Proper programming techniques can offer significant response time improvement and reduce
undesirable transients at the output. The key to performance optimization is to minimize mode
changes (voltage mode/current limit to current mode/voltage limit or vice versa). Mode changes
should be limited to changes in load conditions (to which the power supply will respond auto-
matically), or by programming the limit parameter when required by the user application.
The proper way to program the supply is to initially program the operating parameter to zero and
the complementary limit parameter to the desired maximum value. Subsequent commands
should change only the operating parameter. (The operating parameter is the parameter that
controls the output, e.g., voltage controls the output in voltage mode, current in current mode.)
The complementary limit parameter should be programmed only when there is a need to
change it.
3.6.1 EXAMPLE OF PROPER PROGRAMMING
Assume the power supply is intended to operate in a test application that requires a set of spe-
cific output voltages. The initial set of commands should program output voltage and current
limit. If the same current limit applies to the rest of the test, all subsequent commands should
only program output voltage.
3.6.2 EXPLANATION OF PROGRAMMING TECHNIQUES
Kepco's auto-crossover digital supplies can operate in either voltage mode with current limit, or
current mode with voltage limit. The operating mode is determined by the voltage and current
commands received, as well as the load.
Each time voltage and current commands are received, the unit must evaluate the commands
and the load conditions to determine the proper operating mode. Reducing the number of times
this evaluation must be made is desirable because Kepco's digital auto-crossover supplies
employ two separate feedback loops. Each time there is a potential mode change, there is
always an uncontrolled period of a few milliseconds while the two feedback loops compete for
control of the output. In addition to increasing the time before the output reflects the pro-
grammed command, undesirable transients may also be present at the output during this
period.
By sending only the operating command, there is no doubt as to what the operating mode will
be, so the unit is never uncontrolled, response is quick and no transients are possible.
3.7 SCPI PROGRAMMING
SCPI (Standard Commands for Programmable Instruments) is a programming language con-
forming to the protocols and standards established by IEEE 488.2 (reference document
ANSI/IEEE Std 488.2, IEEE Standard Codes, Formats, Protocols, and Common Commands). SCPI com-
mands are sent to the BHK-MG 40W Power Supply as ASCII output strings within the selected
programming language (PASCAL, BASIC, etc.) in accordance with the manufacturer’s require-
ments for the particular GPIB controller card used.
Different programming languages (e.g., BASIC, C, PASCAL, etc.) have different ways of repre-
senting data that is to be put on the IEEE 488 bus. It is up to the programmer to determine how
to output the character sequence required for the programming language used. Address infor-
mation (GPIB address) must be included before the command sequence. (See PAR.3.3.3 to
establish the BHK-MG 40W Power Supply GPIB address.)