Trying to scope Bacnet MSTP

Which product is right for your exact requirements
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Numbawunfela
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Trying to scope Bacnet MSTP

Post by Numbawunfela » Sun Jun 17, 2018 10:02 am

I am looking for the proper Oscilloscope to look at RS485 communications for BacNet MSTP, Modbus, Johnson N2, and so on. I need to see if there is noise on the line, voltages are right, and other things that can tell me if there are wiring issues. I see things like a lack of termination, ungrounded shields, shields used as a reference conductor, insulation worn through so a conductor is shorted to the shield and grounded, grounding issues.... and so on.

I suppose the pertinent specs for you are:
Speed of signal - 9600 bps up to 115200 bps. Typically I deal with 38400 and 76800.
Voltages - about 2.3vdc and 2.7vdc
I see 2 and 3 wire trunks. They are + and - and sometimes a reference. Usually systems are 2 wire referencing a 24v ac (which can be as high as 29v in practice) common that may or may not be grounded.

I would like to avoid smoking my scope when trying to reference a 24v common, accidentally touching the hot lead on the power supply and exceeding the 20v max on the inputs. Or trying to reference the + and - on the comm trunk, having them short through my Oscilloscope, and smoking a transceiver.

Thanks for the assist!

Gerry
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Re: Trying to scope Bacnet MSTP

Post by Gerry » Wed Jun 20, 2018 10:06 am

Hi Numbawunfela,

Most of your question has already been answered elsewhere on our forum (see here: topic22841.html). Regarding your concern of accidentally touching a 29V line, our 2000 series PicoScopes have overvoltage protection to ±100 V (DC + AC peak, see under 'Oscilloscope — vertical [analog inputs]' here: https://www.picotech.com/oscilloscope/2 ... ifications).

Regards,

Gerry
Gerry
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Numbawunfela
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Re: Trying to scope Bacnet MSTP

Post by Numbawunfela » Fri Jun 22, 2018 2:21 am

Thanks for the clarification, I appreciate your taking time to respond

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