29
EN
Instruction Manual
SCPI Commands for Electronic Loads
Date: 23-07-2015
SCPI
3.9 Special commands
3.9.1 SYST:DATA:SET and SYST:DATA:REQ
Note
This section only applies to the Ethernet cards IF-E1, IF-
E2 and IF-E1B!
Only via the Ethernet
port, the network card is working with
SCPI commands, which are described starting section 3.
In addition, the card provides two extra commands which
can be used to send a telegram to the device in hexadecimal
form, which is similiar to the object orientated binary protocol
(as described in the external guide „
Programming
“). Purpose
of these commands is to control features of the device where
no particular SCPI is available for. So you can even control
the PSI 9000 or PSI 8000 series function manager via these
two SCPI commands. In order to do this you only need to
build a telegram like this:
SYST:DATA:SET
ON, DATA
resp.
SYST:DATA:REQ
ON
All
ON
and
DATA
bytes are decimal values and are sent to
the device with the SYST:DATA:SET command.
Important:
All bytes must be seperated by commas!
DATA
is required when sending something to the device,
like a set value or a status. The number of
DATA
bytes must
be correct, else the device will return an error. The
DATA
length is defined in the object lists (see external
object lists
)
and varies from object to object.
For example, when sending a voltage set value, a 16 bit
integer is required, which results in two bytes and two
comma seperated decimal values for the SYST:DATA:SET
command.
The first value,
ON
, represents the object number (i.e. like
a command) from column 1 of the object lists. It defines the
target for
DATA
. The combination of object number and data
is considered as a set command, while the object number
alone is considered as a query command.
Example 1:
The level control shall be set to „Level A/B“, dynamic mode.
Given that the e-load is already set to remote control and
according to the
object list
for EL3000/EL9000, object 54
has to be used. The list defines bits 5 and 6 of control byte
to select the Level mode, where the binary value 10 will set
„Level A/B“. So the control byte will be hex 0x40 and decimal
64. The required mask will be hex 0x60 and 96 decimal.
The mask selects the bits to change and to initiate a certain
reaction by the control byte without effecting the other bits.
The resulting SCPI command looks like this:
SYST:DATA:SET
54,
96,
64
For further information about the meaning of the values
refer to the external guide „
Programming
“ and the related
object lists
.
Example 2:
The actual values of voltage, current and power shall be
queried from the device. This is done by a REQuest. Accor-
ding to the object lists, the object 71 returns all three actual
values at once in form of six single bytes. The request would
look like this:
SYST:DATA:REQ
71
The device will, for example return, six decimal values:
71,
67,
37,
21,
127,
24,
16
The first value is the object, the rest is the actual values. Two
subsequent values build a 16 bit value, which represents
the actual value as per cent. So the 6 values result in these
hexdecimal, combined values:
67,
37,
21,
127,
24,
16
0x4325, 0x157F, 0x1810
The calculation into decimal or hexadecimal per cent values
can also be done like this (VB, C or similiar):
Per cent value = First value * 256 + Second value
For the first two bytes of the example above, this will calcu-
late to a decimal of 17198, ie. 67 * 256 + 37, which again
represents the hexadecimal value of 0x4325.
The order or the resulting three 16 bit values is defined:
Firrst value is actual voltage, the second the actual current
and the third the actual power, each in per cent of the no-
minal value of the device. After this, they need to be calcu-
lated to real values. See section 1.7 of the external guide
„
Programming
“.
In order to translate the calculated per cent value into a
real actual value, the nominal values of the load required
as reference. Let‘s say the load has 80 V, 200 A and 4800
W, like with a EL9080-200. A second formula would be this:
Real actual value = Nominal value * per cent value / 25600
For the example above and the per cent value of the current
0x157F, it would result like this:
200 A * 5503 / 25600 = 43 A
Note
This example corresponds to the SCPI command
MEAS:ARR?. It means, that the command would return
the same values as the calculated ones. It may occur that
values returned by MEAS:ARR? command slightly differ in
the decimal places due to a small translation error.
Содержание IF-E1
Страница 17: ......
