The "Hi-Z feature" is simply a way for you to tell the signal generator what load it is connected to. The reason this feature exists is so that the signal generator can more accurately display the voltage amplitude at the load. More detailed explanation below.
Would it damage the generator if I hooked it up to a circuit in the wrong range?
Answer: no, there is no risk of damage - all that happens is the displayed value for output amplitude changes.
The signal generator has a fixed output impedance of 50Ω; this does not change, it is always present with all settings, as the manual explains on page 67 (refer image below).
Link for above image:
https://int.siglent.com/upload_file/user/SDG1000/SDG1000_UserManual_UM02010-E08B.pdf
There are several practical reasons for this, one of which is to protect the sig-gen from being overloaded when the output is short-circuited.
When you connect your sig-gen to a load, this is what the overall circuit looks like (assuming the cable is ideal, ie: has negligible impedance compared to [Rout] and [R_load]):
simulate this circuit – Schematic created using CircuitLab
[Node1] is the output of the ideal sig-generator with an output impedance of 0Ω, this is inside the sig-gen and the user (you) cannot get to it.
[Node2] is the output terminal of the sig-gen, which is what you connect your cable to.
Here is the key idea:
The sig-gen controls the voltage at [Node1], but displays the voltage at [Node2] according to what you set for parameter:
If this is set to "Hi-Z" then the displayed value is simply the same as the controlled value.
The voltage at the load [Node2] is not the same as the voltage at [Node1]; there will be a voltage drop due to [Rout]. The sig-gen does not "know" the voltage at [Node2] it only "knows" voltage at [Node1] - it "knows" this because you tell it, by setting up the parameters associated with voltage amplitude.
You, as the user, want to know the voltage at the load, which (for the purposes of this discussion) we shall assume to be the same as the voltage at [Node2].
If the load is 1kΩ as shown in the above schematic, the voltage at the load will be almost (but not quite) the same as the voltage at [Node1]. You can calculate it accurately from the usual resistor-divider equation:
[Node2 volts] = [Node1 volts] * ( 1000Ω / (1000Ω + 50Ω) )
= 0.952 [Node1].
So the voltage at the load will be 95% of the voltage at [Node1] - which is not perfect, but accurate enough for most uses. If you set the sig-gen to output a DC voltage of 1.00V with no AC component, here is what the Sig-Gen will display as the output voltage for different values of the parameter "Load Setting":
| # |
Load Setting |
Sig-Gen Display |
Actual V measured at load |
| 1 |
Hi-Z |
1.00Vdc |
0.95Vdc |
| 2 |
50Ω |
0.50Vdc |
0.95Vdc |
| 3 |
1kΩ |
0.95Vdc |
0.95Vdc |
Note: Row #3 of the above table may not be correct. According to the manual, it seems you can set this parameter freely to any value, however, I have not used this product myself so cannot be sure this is how it will work; I suggest you try it out yourself - you can't do any damage to the sig-gen by changing this parameter setting.
If you set the sig-gen to output a sinewave of 1kHz & 1.00Vp-p, then a scope connected across the load will show the sinewave to have an amplitude of 0.95Vp-p.
The 50Ω output impedance is industry-standard practice, done to ensure that the unit can drive standard 50Ω co-ax cables and other 50Ω standard loads to avoid the problems caused by incorrectly terminated transmission lines (that is a separate topic).
Below: the relevant section of the manual, for convenience.
Link for above images:
https://int.siglent.com/upload_file/user/SDG1000/SDG1000_UserManual_UM02010-E08B.pdf
