I need to do oscilloscope testing on BAS networks talking over RS485. Protocols like modus, BacNet, Johnson N2, and others. I need to know if your product line includes anything that can help with this.
The pertinent specs for my use I suppose is:
Voltage: +-5vdc all the time, with 24vac (typically 22v to 29vac in practice) on occasion if possible.
Comm speed: 9600 bps, up to 115200 bps. I see 78600 and 38400 most frequently.
I will be most commonly be using an oscilloscope measuring differential between the + and - on the comm trunk, occasionally between + and a reference, and - and the same reference. The reference is usually the common leg of a 24vac transformer, but it can also be ground or a provided, dedicated reference wire.
I need to use an Oscilloscope to find ground loops causing a voltage offset, noise from a VFD or lighting ballast, lack of termination, or improper voltage biasing, capacitance in the wire preventing the voltage from reaching the amplitude necessary to trigger a 0 or 1 value, shorts in the cable from rubbing or cutting that has voltage draining from a conductor to shield or between conductors.
So first off, is the Analog Discovery 2 able to provide useful data? Is its oscilloscope able to provide readings on this type of network with good enough resolution that I can see the issues I am looking for?
Secondly, what is the best way to hook it up?
I was looking at the BNC connector board, as it provides the typical Oscilloscope probe connections. But then I noticed that it changes differential terminals into Single Ended ones and wondered if you may not have something better. For example, can I pull Oscilloscope readings from the Pmod RS485?
My life is sitting on a bucket in a basement programming Air handlers and mechanicals... so the likelihood of shorting out this Analog Discovery 2 by touching a Single End ground clip to the wrong thing is plausible, and shorting out my controller's RS485 transceivers is likely. Crap happens in mechanical rooms. I would much rather use differential connections. If I could add the to Analog Discovery 2 to the trunk using the Pmod-RS485 and scope it - that would be beyond perfect.
Question
Numbawunfela
I need to do oscilloscope testing on BAS networks talking over RS485. Protocols like modus, BacNet, Johnson N2, and others. I need to know if your product line includes anything that can help with this.
The pertinent specs for my use I suppose is:
Voltage: +-5vdc all the time, with 24vac (typically 22v to 29vac in practice) on occasion if possible.
Comm speed: 9600 bps, up to 115200 bps. I see 78600 and 38400 most frequently.
I will be most commonly be using an oscilloscope measuring differential between the + and - on the comm trunk, occasionally between + and a reference, and - and the same reference. The reference is usually the common leg of a 24vac transformer, but it can also be ground or a provided, dedicated reference wire.
I need to use an Oscilloscope to find ground loops causing a voltage offset, noise from a VFD or lighting ballast, lack of termination, or improper voltage biasing, capacitance in the wire preventing the voltage from reaching the amplitude necessary to trigger a 0 or 1 value, shorts in the cable from rubbing or cutting that has voltage draining from a conductor to shield or between conductors.
So first off, is the Analog Discovery 2 able to provide useful data? Is its oscilloscope able to provide readings on this type of network with good enough resolution that I can see the issues I am looking for?
Secondly, what is the best way to hook it up?
I was looking at the BNC connector board, as it provides the typical Oscilloscope probe connections. But then I noticed that it changes differential terminals into Single Ended ones and wondered if you may not have something better. For example, can I pull Oscilloscope readings from the Pmod RS485?
https://reference.digilentinc.com/reference/pmod/pmodrs485/start#example_projects
Or the Pmod-ad5?
https://store.digilentinc.com/pmod-ad5-4-channel-4-8-khz-24-bit-a-d-converter/
My life is sitting on a bucket in a basement programming Air handlers and mechanicals... so the likelihood of shorting out this Analog Discovery 2 by touching a Single End ground clip to the wrong thing is plausible, and shorting out my controller's RS485 transceivers is likely. Crap happens in mechanical rooms. I would much rather use differential connections. If I could add the to Analog Discovery 2 to the trunk using the Pmod-RS485 and scope it - that would be beyond perfect.
Link to comment
Share on other sites
6 answers to this question
Recommended Posts
Archived
This topic is now archived and is closed to further replies.