Analogue And Grounding Question

[richleva]

Hello,


I had debate with Coworker involving Grounding and Analogue.
We Build and manufacture PLC enclosures, should the ground terminal blocks (where the field devices terminate to) be isolated from the grounded Din Rail, And have wires running straight to the ground Bar/Bus. Or.. Can we just use ground terminal blocks that bond directly to the Din Rail?


Does the ground terminal blocks need to be isolated from the Din Rail and wired directly to the ground Bar?


In my mind its the Same Thing? Same ground reference.


Apparently the 60hz from the 120Ac has a different affect on the two different installations??


Does it actually matter?
If this is not clear please let me know

 

[Tom Jenkins]

In my opinion, all grounds should be at the same potential, wired together, and tied to a good, solid earth ground.

 

[Super Koop]

Analogs are a bit safer, but for sure there should be grounding in addition to a shield/gnd.

Recently had an instance with a high speed counter card catching flow-meter pulses.
Shield was properly connected, but we were getting noise back from a nearby pump. My counters were going nuts, and we could not validate the volumes. Had to run an additional ground to the plumbing.

 

[danw]

A friend of family worked for Westinghouse and did contract work for the DoD at the Distant Early Warning (DEW Line) radars in Canada during the 1950's/60's cold/nearly hot war period.

He learned a whole lot about grounding for radars and instrumentation based on structures sitting on ice. Lots of heavy braided copper and copper 3/4"x3/4" bars and brazed connections.

You know you're getting old when you write stuff like this - not particularly relevant, but wanting the world to know that getting radars to track US bombers simulating Soviet bombers coming over the pole was an on-going engineering effort.

 

[drbitboy]

...You know you're getting old...

Old or not, this is cool.


Warfare advances technology (video games too).


Talk about a double-edged sword .

 

[parky]

Analogue screens/shields should be grounded at one point only to reduce what are often called earth loops, I suggest grounded at one end (usually plc /controller side) often it is better to wire directly to the input but if that is not practical, then continue the screen (Shield) or grounding wire through a terminal (not earth) and ground it as close to the instrument i.e. PLC card/ controller.