I am considering buying a scope for work, I do not think my employer will cover this, so cost is a consideration.
I am new to oscilloscopes and have an opportunity to learn how to troubleshoot and analyze different circuits.
Essentially, I want to use this on different industrial communication protocols such as:
Modbus TCP/IP and RTU including RS-485 and RS-232
Profibus
HART
EtherCAT (nice to have)
Additionally, it would be nice to test 600VAC VFDs
Questions:
1) Are two channels sufficient? What situation would I use 4?
2) Should I get MSO and what would its purpose be in the above protocols?
3) What do I need to test Ethernet?
4) What is a comfortable amount of memory/bandwidth/sampling for the above protocols?
are the 2000 series capable enough, or will I wish I went with the 3000 series? I was considering the 3204D or 3404D with or without MSO.
For all ethernet base protocols you will be better of with wireshark.
For 485 and 422 based protocols the best you need or a differential probe or use 2 ch per data stream and a math A-B function to see the clean signal.
On your desk you can do with 1 channel per data stream (RX/TX) but in industrial situations you will need the differential signal to trouble shoot.
differential probes are expensive (unless you buy a 4444 that has 4 differential inputs)
I would use a 4 channel scope so you can use a digital output on the PLC or other controller to trigger the scope and capture the bus on the trigger moment.
If I have time and don't forget it I will post some captures of polluted signals where the differential signal is ok.
An other example why differential probes only tell half the story.
Black would be the only signal you see with a differential probe, the blue and green gives the individual signals compared to ground on the bus, and the black is calculated from A-C
Benno
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