16
Gossen Metrawatt GmbH
2.3.4
Constant Power Mode (CP)
There are two sorts of constant power modes, the Constant Power-Voltage Source mode (CPV) and the Constant Power-Current
Source mode (CPC). The CPV mode is applied to voltage source test, and the CPC mode is applied to current source test. In CP
mode, the load consumes the constant power in accordance with the programmed value regardless of the changes of external current
and voltage (see Figure 2.4). Press the
key to enter into mode selection and parameter setting menu. Choose CPV or CPC mode
with
▲
and
▼
keys.
Input the power value via Entry keys or the knob with
◄
and
►
keys. Use
Enter
key for confirmation. The CP mode and parameters can
also be set via remote command (MODE CPV, MODE CPC, POWer <NRf+>).
Figure 2.4
Constant Power Mode (CP)
Figure 2.5 shows the current-voltage curves for several common power supplies. The constant power curve is a hyperbola in the first
quadrant. The constant power curve usually intersects with current-voltage curve at two points (the CPV point and the CPC point)
when the power of the external power supply is larger than the set power. At the CPV point, the power supply shows the feature of
voltage source: the output power will be increased with increasing current; at the CPC point, the power supply shows the feature of
current source: the output power will be increased with increasing voltage. SPL Series electronic load can be set at any one of inter-
section points to be operated by the user.
Figure 2.5
Current-voltage Curves for Normal Power Supply
As it adopts the advanced slope detection method, SPL 250-30/SPL 400-40 Series electronic load only needs to test a part of the cur-
rent-voltage curve to know whether the two curves (constant power curve and current-voltage curve) intersect. Therefore, when the
set power is larger than the actual power, the external power supply will not be short-circuited by the load for the insufficient power.
When the load detects that the power of the external power supply is insufficient, it will try to find constant power point automatically till
the set power is met.
2.3.4.1
Setting Ranges
The setting range for the power setpoint value for both CPV and CPC mode is 0 ... 250 W (SPL 250-30), for 0 ... 400 W (SPL 400-40),
for 0 ... 200 W (SPL 200-20) and for 0 ... 350 W (SPL 350-30).
2.3.4.2
Immediate Power Level
The immediate power level refers to the power set value in CP mode, which can be set via mode selection and parameter setting
menu, or via remote command (POWer <NRf+>). The immediate resistance level can also be modified directly with
◄
►
cursor keys
and the knob.
2.3.4.3
Triggered Power Level
The triggered power level refers to the preset power value, which can become immediate power level automatically when a trigger is
received. If the CP mode and the input are enabled, the input will be updated immediately when a trigger occurs. If the CP mode is not
active, this power level will have no effect on the input until the CP mode becomes active. The triggered power level only can be set via
remote command (POWer:TRIGgered <NRf+>). Once a power level is triggered, subsequent triggers will become invalid until another
(POW:TRIG<NRf+>) command is received. The trigger operation will be described in later chapters. The status register of the electronic
load can keep track of pending triggers and other operating conditions, which will be described in detail in the “SPL SCPI Programming
Guide”.
Constant Power Curve
U/I Characters of Power Supplies
CPV Mode
CPC Mode
V
V1
V2
I1
I2
I
