KEPCO BIT 4886 Operator Manual - Manual (Page 36)

4-2
BIT 4886 120413
and thus the output current (where s = sign, + or – and xxxx = the absolute value of out-
put current). Sending VOLT sxxxx controls voltage limit (where s = sign, + or – and xxxx
= the absolute value of voltage limit.
4.1.1.2 AUTOMATIC RANGE OPERATION.
The BIT 4886 has low and high ranges which are changed automatically when the main channel
set point is changed from a value less than the 1/4 of the units operating capability to a value
that is higher than 1/4 of the operating capability. The automatic gain change is enabled at
power up, or by either the *RST command or a mode change command (FUNC:MODE).
An automatic range change can result in undesirable transients when passing through the quar-
ter scale point as result of BIT 4886 card gain change, depending upon the load at the output of
the BOP. For example, with a 50V BOP in voltage mode, the quarter scale gain change is at
12.5V. When the unit is programmed from 12.5V to 12.6V, the gain of the BOP changes and a
spike may be seen at the BOP output. A transient may also occur when changing from –5V
volts to +50V as –5 volts is in the region between –12.5V and +12.5V and +50V is beyond the
quarter scale region. When the unit is programmed to remain in full scale, the gain change
does not occur and this eliminates the transient.
4.1.1.3 USING THE BIT 4886 TO PRODUCE A SOFTWARE-TIMED RAMP AT THE BOP OUTPUT
If the power supply is intended to operate in a test application that requires a set of specific out-
put voltages in a specific order and the number of points is more than the 1000 points available
in the BIT 4886 LIST command, a computer-controlled ramp can be used.
The recommended way to run a voltage ramp is to set the current limit to maximum plus at least
2% (or unit limit for max absolute value of the load). While in voltage mode, current limit is the
absolute value of the programmed current.
Before running the ramp it is recommended that the scale be set to full scale using
VOLT:RANG 1 to avoid any transients as explained in PAR. 4.1.1.2.
When installed, the Labview interactive example available on our web site creates a KpDCpwr
directory in Labview's user.lib. This sub-directory contains various programs such as KepcoDCPwr
Software Timed Ramp.vi. This vi is a software-timed linear ramp that is an example of using both
the range command and the limits in generating a ramp. There is also a KepcoDCPwr Software
Timed Current Ramp.vi for the same functionality in current mode.
4.1.2 MAKING SURE THE PREVIOUS COMMAND IS COMPLETE
Some SCPI commands require a flash memory update and can take an indeterminate amount
on time to complete. These commands are:
• *SAV
• MEM:PACK
• MEM:UPD
• CAL:COPY
• CAL:SAVE
• SYST:PASS:NEW
• SYST:SEC:IMM
When sending these commands via the GPIB, these commands require a query to be added to
the command string to verify the previous command is complete. When the command is com-
plete, the unit updates the status byte and indicates MAV (Message Available, bit 4 - see Table
A-3) is true. MAV indicates that there is a response to be received by the computer, so when it