There are usually several waveforms output by a function generator. The one that most resembles a ramp is called a sawtooth. Look at the link to see the other choices.

If the waveform slopes up and then goes down with the same slope, you would call it a triangle wave, but yours sounds like a sawtooth.

Technically a ramp should be a single straight line (between two points). Presumably that's what is intended with the description "Zwischen diesen Zeitpunkten wird das Signal durch das Gerät kontinuierlich verändert".
However, in the progression
Bei 0s Sekunden: 0%
Bei 5s Sekunden: 20%
Bei 10 Sekunden: 50%
Bei 15 Sekunden: 30%
there are four reference points specified and thus three linear segments (or 'ramps') — one segment between each pair of sequential points.
So while a single segment (╱, say) is well described as "a ramp", a sequence of segments (︿/︺W﹀\︹︿, say) strictly speaking comprises multiple ramps. (And, indeed, potentially some flat [horizontal] segments, which are not often thought of as 'ramps'.)
Industrially maybe you could casually still call such a sequence 'a ramp'. Or 'a ramped/ramping function'.
Mathematically speaking you would want to be more precise and call it a piecewise linear function, or a linearly interpolated function.
In the context of generating signals, it might be possible to refer to a piecewise linear trace/profile/signal/function, or a linearly interpolated trace/profile/signal/function. (Although these are more wordy.) "Profile" & "function" are better for what's been specified (ideally), whereas "trace" & "signal" are better for what's been measured (in reality)
Again, whether such a wordy phrase is necessary depends on whether a distinction needs to be made to other profiles — for example, if the device also generates sinusoidal signals, which are continuously varying and do not contain any ramps. If the device were only capable of generating piecewise linear signals, then most of the time you could refer to simply the "trace/profile/signal" without losing any information. (Function is a bit tricky, because it can be more easily misunderstood in the absence of the proper context.)

If the signal happens to be periodic (i.e. cyclical), then it might be described as having a sawtooth or triangular profile. And we would be more inclined to start talking about it as a "wave" or a "waveform".
The progression given above does not exhibit any clear periodicity.

The term that bothers me the most here is "Rampen-Bildschirm".
I am guessing that this is a screen/monitor used to display the signal (visually). I cannot be sure about the German, but "ramp-screen" sounds awful to me in English. If it's the only screen/monitor/display on the device, then one option would be to simplify the name to just "Bildschirm" ~ screen/monitor/display. If more precision/formality is preferred, then better may be something like "trace display screen/monitor" or "signal display screen/monitor". Or possibly "scope" (https://en.wikipedia.org/wiki/Oscilloscope)
Cf. https://patents.google.com/patent/US5852789 , http://www.patents.com/us-6556202.html , https://telonicinstruments.co.uk/rigol-uk/DS/DS1000D-TK User...

"Slope" is not a very fitting word to describe either the linear segments (although it might characterise them, because the 'slope' one of the properties of a straight line) or the display screen/monitor.

--------------------------------------------------
Note added at 34 days (2018-03-03 11:18:27 GMT) Post-grading
--------------------------------------------------

As I had guessed, there are almost no 'hits' online for the phrase "Rampen-Bildschirm". Even fewer if we exclude this ProZ thread and also the client's old/current product manual. So it seems to be not particularly idiomatic in German either. There are also a smattering of 'hits' for "Rampenbildschirm", but not for a device similar to that described above.
For example, one device that uses this uncommon term appears to relate only to single ramps (linear changes in pressure).
https://www.resmed.com/epn/dam/documents/products/machine/vp...
https://www.resmed.com/epn/dam/documents/products/machine/vp...