Coupling on Rigol scope - Page 1
Forum section: electronics / beginners

author: stitch
author_rank: Regular Contributor
timestamp: September 01, 2011, 01:40:53 am
content: I am a new owner of a Rigol DS1052E Oscilloscope.Under the channel menus are coupling options: DC, AC, and GND. There is also a coupling menu under the trigger menu. You get to the trigger coupling menu this way: Trigger menu button>Set Up>Coupling. The choices under the trigger coupling menu are: DC, LF Reject, HF Reject, AC.Right now, I'm not concerned with LF Reject or HF Reject. What confuses me is that there are DC and AC coupling choices under both the channel menu and the trigger menu. Can anyone help me understand what is the purpose of having these two places to set AC or DC coupling? Do they conflict?

author: Computeruser
author_rank: Regular Contributor
timestamp: September 01, 2011, 01:45:35 am
content: It is the same basic setup on oscilloscopes going back years (decades). If your signal is a small AC signal riding on top of a larger DC component, you need to use (want to use?) AC coupling on your input channel just to see the small signal only.Now exactly the same thing holds true if you want such a signal to trigger your scope. If you are trying to trigger from a small AC component on top of a larger DC component, you need to use AC coupling or else the DC component would swamp the trigger. ... C

author: stitch
author_rank: Regular Contributor
timestamp: September 01, 2011, 03:57:27 am
content: Thank you. I am going to experiment with it.

author: Computeruser
author_rank: Regular Contributor
timestamp: September 01, 2011, 06:46:53 pm
content: Cheers. Let us know if we can help. ... C

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 02, 2011, 12:18:05 am
content: GND... what is GND coupling?

author: joelby
author_rank: Frequent Contributor
timestamp: September 02, 2011, 12:22:07 am
content: Quote from: Mechatrommer on September 02, 2011, 12:18:05 amIt sets the input to GND, which is useful because you don't always know where ground is due to the vertical axis adjustment. It's a bit less useful on modern oscilloscopes that have a vertical offset readout on the screen.

author: Mechatrommer
author_rank: Super Contributor
timestamp: September 02, 2011, 12:43:33 am
content: Quote from: joelby on September 02, 2011, 12:22:07 amit sets the +ve probe to gnd? yea that make sense because when i set to that coupling, all i get is a flat zero line (since the -ve probe is already ground). so can we make this as the most nonsense feature on modern dso? with the gnd (-ve) probe already at the gnd?

author: joelby
author_rank: Frequent Contributor
timestamp: September 02, 2011, 12:46:00 am
content: Yeah, it's not that useful these days, although if it effectively connects the input to ground using a relay rather than just replacing the ADC's output with zeros, it can be useful for examining the oscilloscope's noise floor if you don't have an external BNC short.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 02, 2011, 07:25:30 am
content: The ground position puts a true ground on the 'scope input,& is a lot quicker than finding a shorted BNC among the assorted pads,adaptors,etc lying on your bench!.It's not as quick as just shorting the earthing lead & probe tip,but it doesn't act as an RF pickup loop,like that does.It also allows you to see if the vertical offset readout on the 'scope is lying in its teeth!VK6ZGO

author: w2aew
author_rank: Super Contributor
timestamp: September 02, 2011, 12:16:38 pm
content: Quote from: stitch on September 01, 2011, 01:40:53 amEven though this description of the Trigger coupling controls is for a classic Tek 465B analog scope in this video, the concepts for trigger coupling are exactly the same. Hopefully this will answer your questions about trigger coupling...

author: ejeffrey
author_rank: Super Contributor
timestamp: September 02, 2011, 12:31:25 pm
content: Quote from: Mechatrommer on September 02, 2011, 12:43:33 amIt doesn't ground the probe (which would short out anything the probe is connected to), it connects the scope input to ground instead of to the probe to give you a clear reading of zero volts DC. Old analog scopes didn't have a little tick mark on the side of the display to show you the vertical offset and the ground switch was the easiest way to adjust the vertical offset. It isn't really necessary on DSOs, but people are used to seeing it.

author: stitch
author_rank: Regular Contributor
timestamp: September 02, 2011, 03:26:16 pm
content: Thanks for the direction, w2aew. I couldn't understand why they would have AC and DC coupling menus in two different places on the scope. The video helps a lot.