EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: kuifje on February 14, 2019, 07:39:42 pm
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Hello,
I just got the Rigol DS1054z and I can't find the 50 ohm input setting.
Normally on digital oscilloscopes you can select load resistance. Why not on this one?
Already looked in the datasheet but can't find anything.
Thanks!
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There is none ... just like on many entry level scopes. If you need a 50Ohm input, use a 50 ohm feedthrough terminator.
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Uh... that sucks, because they didn't deliver the 50 ohm feedback terminator.
It is "feed through", and it is not included with the scope. There are plenty of options on eBay. For example https://www.ebay.com/itm/50-Ohm-Feed-Through-Terminator-BNC-to-BNC-50KY-Device-Q9-Adapter-Black/173224204575 (https://www.ebay.com/itm/50-Ohm-Feed-Through-Terminator-BNC-to-BNC-50KY-Device-Q9-Adapter-Black/173224204575)
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I'm new to this website, I have a question too about a function generator, should I make a different thread or can I just comment here?
Make a new one.
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Oscilloscopes with bandwidths of 100 MHz and below do not usually include switchable 50 ohm terminations. If you must, then a BNC-T and BNC 50 ohm terminator can be used at lower frequencies.
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Uh... that sucks, because they didn't deliver the 50 ohm feedback terminator.
It is "feed through", and it is not included with the scope. There are plenty of options on eBay. For example https://www.ebay.com/itm/50-Ohm-Feed-Through-Terminator-BNC-to-BNC-50KY-Device-Q9-Adapter-Black/173224204575 (https://www.ebay.com/itm/50-Ohm-Feed-Through-Terminator-BNC-to-BNC-50KY-Device-Q9-Adapter-Black/173224204575)
Lemme ask a stoopid question. Does measuring that termination with a DMM demonstrate anything valuable?
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Lemme ask a stoopid question. Does measuring that termination with a DMM demonstrate anything valuable?
Yes, it shows that there is actually a resistor inside. This is not a guarantee with Chinese products :).
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Lemme ask a stoopid question. Does measuring that termination with a DMM demonstrate anything valuable?
It gives you the DC resistance; but it will not tell you much about the terminator's behavior at high frequencies (where capacitance and inductance come into play). In other words, a DC resistance reasonably close to 50 Ohms is a necessary, but not a sufficient condition for good termination.
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I guess that is likely to be good enough for the application. I've made a few terminations using SMD resistors and a BNC connector.
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I guess that is likely to be good enough for the application. I've made a few terminations using SMD resistors and a BNC connector.
Since you don't tell us what "the application" is, it's tough to comment on that statement. :P
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Diy is good enough for 100MHz, probably up to 500MHz..
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I have a related question.
Say you have your scope connected to a 30VDC power rail with a coax or X1 probe, and you accidentally hit the 50 ohm impedance button. Now you have 0.6A (0.6A=30/50) going into the scope, and the scope is dissipating 18W (18W=30*30/50). I think this would damage the scope. Am i right, or am I missing something? It bothers me a lot that you could blow up your scope by accidentally pushing a single button.
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I have a related question.
Say you have your scope connected to a 30VDC power rail with a coax or X1 probe, and you accidentally hit the 50 ohm impedance button. Now you have 0.6A (0.6A=30/50) going into the scope, and the scope is dissipating 18W (18W=30*30/50). I think this would damage the scope. Am i right, or am I missing something? It bothers me a lot that you could blow up your scope by accidentally pushing a single button.
Yep. Thats why most scopes that have, or are only 50 Ohm have a warning that says "Do not exceed 5Vrms". Because if you're DC coupled, you're going to have a very, very bad time. All that energy will be dissipated in the matching method they use (probably just a 50r resistor).
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I have a related question.
Say you have your scope connected to a 30VDC power rail with a coax or X1 probe, and you accidentally hit the 50 ohm impedance button. Now you have 0.6A (0.6A=30/50) going into the scope, and the scope is dissipating 18W (18W=30*30/50). I think this would damage the scope. Am i right, or am I missing something? It bothers me a lot that you could blow up your scope by accidentally pushing a single button.
X1 probes can have considerable series resistance which is higher than 50 ohms but in general what you say is correct. Well designed oscilloscopes monitor the input voltage level and disengage their internal 50 ohm termination if a dangerous overload is detected to protect their internal termination.
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I guess that is likely to be good enough for the application. I've made a few terminations using SMD resistors and a BNC connector.
Since you don't tell us what "the application" is, it's tough to comment on that statement. :P
The topic context is about the OP and a DS1054Z. I'm thinking that most use cases for this scope is likely not to be effected much by a poorly RF matched through termination. I don't typically make very sensitive measurements with my scope, though. I guess using a wire-wound resistor might cause problems? Could make one worse than serialing 25, 2W wire-wound resistors? That would look like a foot-long coil.
The terminations I made used 4 radially mounted SMD resistors and that application was for single port OSL reflectometer calibrations up to around 4 GHz. If I remember correctly, they performed very well when compared to a commercial calibration T from the German company. This is just for field level applications.