Background:
I am a junior engineer who work with testing and designing inverters for motors. I have been looking at a new oscilloscope since the one I had gave up. There are alot of Tektronix TPS2024b being used since it has dedicated isloated channels on it. I was not sure how isolated channels worked to begin with but I now understand their usefullness. It is very hand to have a scope being able to do the same measurements as a multimeter without making mistakes, but also very nice to be able to avoid long paths to ground for more precise measurments.
So I decided an isolated scope that can measure high and low voltages well would be a a good choice for me, especially since differential probes sometimes can cost quite a bit, and adding that to the cost of the oscilloscope it quickly takes of.
So I started looking and it seems it is quite unusual, very unusual in fact. So I thought it would be a good idea to ask here to see if you can tell me what I am missing. I have noticed that the bandwidth seems lower on the isolated scopes, but it is hard to draw any conclusions with so few alternatives to compare.
Question(s):
- Why are there so few bench osilloscopes with dedicated isolated channels?
- Is it a design issue, a cost issue, a business issue or is it just better with differential probes?
Other:
Oscilloscopes i have found:
- Tektronix TPS2000 series (~15 year old design)
- Cleverscope CS448
- Handyscope HS6 DIFF
There are also some hand held isloated oscilloscopes, I could add to the list but I have not written them down since I was not looking for a hand held scope. USB scopes to me seems very good and like a no-brainer, if it is possible to get one.
Best Answer
It is a cost (price) and demand issue. Most users don't need isolated inputs. Most users have ground-referenced signals so a scope with non-isolated inputs is OK.
Cost is an issue as isolated inputs require more complex circuits compared to the standard solution. This makes the oscilloscope more expensive.
Also note that isolated inputs and differential probes are different things! You can use an isolated input as if it is a differential (floating) input but it's not really the same as the connection on the oscilloscope is a BNC connector which is a single ended input. The two electrical connections on a BNC plug aren't precisely the same, one is also the shield, the other (inner connection) is shielded. For DC and low frequency that usually doesn't matter much but for higher frequencies ore low noise measurements it can matter. Then a true differential probe is the better option.