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EA Elektro-Automatik GmbH
Helmholtzstr. 31-37 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
www.elektroautomatik.de
PSB 9000 3U Series
3.11.2.3 Resolution
Amplitudes generated by the arbitrary generator have an effective resolution of approx. 52428 steps. If the am
-
plitude is very low and the time long, the device would generate less steps and set multiple identical values after
another, generating a staircase effect. It is furthermore not possible to generate every possible combination of
time and a varying amplitude (slope).
3.11.2.4 Possible technical complications
Operation of switching mode power supplies as a voltage source can, when applying a function to the output volt-
age, lead to damage of the output capacitors due to continuous charging/discharging which causes overheating.
Furthermore the actual voltage progression may differ from what’s expected.
3.11.2.5 Minimum slope / maximum ramp time
When using a rising or falling offset (i.e. DC part) at functions like ramp, trapezoid, triangle and even sine wave,
a minimum slope, calculated from the rated values of voltage or current, is required or else the adjusted settings
would be neglected by the device. Calculating the minimum slope can help to determine if a certain ramp over
time can be achieved by the device or not. Example: model PSB 9080-120 is going to be used, with 80 V and
120 A rating.
Formula: minimum slope = 0.000725 * rated value / s
. For the example model it results in ΔU/Δt of
58 mV/s and ΔI/Δt of 87 mA/s. The maximum time which can be achieved with the minimum slope then calculates
as approximately 1379 seconds according to formula
t
Max
= rated value / min. slope.
3.11.3 Method of operation
In order to understand how the function generator works and how the value settings interact, the following should
be noted:
The device operates, including in function generator mode,always with the three set values U,I and P.
The selected function can be used on one of both the values U or I, the other two (here labelled “I Source” resp.
“I Sink” and “P Source” resp. “P Sink”) are then constants and have a limiting effect.
That means if, for example, a voltage of 10 V is set in source mode for the DC output, a load is connected and
a sine wave function should operate on the current with an amplitude of 20 A and offset 20 A, then the function
generator will create a sine wave progression of current between 0 A (min) and 40 A (max), which will result in an
output power between 0 W (min) and 400 W (max). In case the output power is however limited to 300 W, the cur-
rent would be limited to 30 A and, if clamped to an oscilloscope, it would be seen to be capped at 30 A and never
achieve the target of 40 A.
For an even better understanding how the device works in dynamic operation you must read following:
•
The device also has an integrated electronic load, here called “sink”, which is supposed to
discharge the capacitance on the DC terminal when running dynamic voltage changes, i.e
higher voltage to lower voltage, in source mode. This requires a certain current and thus power,
which can and should be adjusted for almost every function described below (parameters “I
Sink” and “P Sink”). For safety reasons, the current “I Sink” is always set to 0 after selecting a
function, which means the sink mode is deactivated for the moment.
•
The sink current as adjustable with parameter “I Sink”, when adjusted unequal to 0, furthermore
discharges capacities which are possibly in the load application and thus this current setting
has to chosen carefully, because it also affects the cross section of cables to the load applica
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tion. Recommendation: I Sink = I
Max
of the curve resulting from the function.
