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Old October 7th, 2017, 05:46 AM   #1
darkesha
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Digital and Analog signal conditioning in Manufacturing ?

Hi, I have 7 years of experience as a maintenance / PLC programmer in a fairly old steel mill. I was the one who converted PLC2 to CtrlLGx platform ten years ago.

After that, I went to Oil and Gas engineering firm where I was able to learn common practices in programming of O&G processing plants, compressors and other.

Since logic in the steel mill was just converted from PLC2 and PLC5 to CtrlLgx there is none of signal conditioning that I see O&G sector uses (Plant PAx system etc...).

I also remember almost all of the digital switches (proxy, limit etc...) are programmed as NO switches.
Another difference is a control voltage for field devices - it's all 120V in manufacturing vs 24V in O&G.


I started to think how much of a benefit would it be to program machinery with normally closed switches or at least as NO with the end of the line resistor for open circuit detection.

Also the signal conditioning used in oil and gas programming practice - do you think it would help in a purely sequencing /digital IO facility vs. process environment with it's 90% analog devices.

So for a professional manufacturing PLC Automation engineers who also have background in O&G or (as my American friend call it) Petroleum industry, what's the current trend in the programming in manufacturing ?

Last edited by darkesha; October 7th, 2017 at 05:50 AM.
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Old October 7th, 2017, 07:03 AM   #2
jstolaruk
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I've been in the auto industry for about 40 years, the last 33 in the controls side of it and added robot programming in the last ten. I haven't seen everything but quite a bit, from glass manufacturing, body-in-white assembly, painting, and final assembly, with the bulk of my time in powertrain (engines, transmissions, axles, etc).

Normally closed switches are routinely used for fail-safe sensing in material handling. Analog devices are normal for machining and assembly (pressing, linear displacement, leak testing, torquing of fasteners, etc).

The current trend is traceability. Laser etching everything with 2D barcodes (plus some human readable) then tracking components through the manufacturing and assembly processes. Just about every station has a connection to a server-DB-in-the-sky that requires the system to query it when processing a part or assembly to check to see that it is indeed in the correct step in the process, then uploading the results of that step.

I'm sure others here have experienced other trends.
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Old October 7th, 2017, 07:12 AM   #3
jstolaruk
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I was thinking of PLC2 conversions. My last was a PLC-2 to PLC-5 about ten years ago. I recall doing a PLC-2 conversion to Controllogix back in the late 90s early 2000s. The big pain was the conversion from a ladder printout and h/w drawings that were found in the bottom of the main panel, oil soaked of course. The machines were big, lots of iron, so the investment by the customer was worth it. Somehow we go the machines running.
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Old October 7th, 2017, 08:41 AM   #4
DwSoFt
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With regards to signal.conditioning. it depends on a few things. Fist of all to shutdown the entire plant is prevented from quick trips on OnG. But in manufacturing they are not.all shutdowns but more position sensors and the process is alot faster so they need the response from the switches faster and thus the conditioning would work against that
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Old October 18th, 2017, 06:38 PM   #5
darkesha
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Interesting point...I wonder what's the potential hit time-wise. I would expect response to be almost instantaneous.
Still hard to fight against open wire alarming on different inputs, even digital NO ones.
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