You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old June 8th, 2004, 04:05 PM   #1
jdcochran
Member
United States

jdcochran is offline
 
jdcochran's Avatar
 
Join Date: Jun 2004
Location: Atlanta GA
Posts: 5
Relays Instead of PLC in High Speed BarCode Application for Pharma???

OK, for my first post, I need a sanity check. For justifiable logistical reasons, I proposed to a client that I might be able to save them lots of FDA validation effort$ on a bar-code scanning operation to augment an existing line. How? By staying out of their existing PLC logic and adding an ancillary device/system that was not subject to extensive code validation and revision controls.

I proposed to accomplish this with a simple prox switch, simple relays, and some relay counters.

Now that I did it, I'm fearing that the line's high-speed indexing rate may byte me in the ASCII.

In essence, a small carton is scanned for pharmacode and compared with an expected result. If a bar code anomaly occurs, the product is rejected. Normally, it would be simple to immediately activate a reject function (in this case, a solenoid is activated). However, the reject action does not occur until later down the line, say 10 cycles later.

At any rate (no pun intended), I sketched out some prelim relay logic code. I have a few other logic decisions to make in the system... but ended up with a prox switch (for trigger), 2 counter relays, and 6 standard relays.

Questions:

1) what is the maximum rate at which todays off-the-shelf industrial relays (24VDC coil) typically respond?

2) in a PLC program, I must concerm myself with scanning sequence. In the hard-wired world, I must be concerned about everything happening at once. Any gotchas I need to consider before implementing a high-speed hard-wired relay system?

3) my line speed is somewhere between 400-600 clicks/min. Is this doable with discrete components? I'll even consider solid-state devices. Any suggestions on high-speed counters relays that could stand up to this speed? Discrete relays that can take the abuse?

I have a vision system as a contingency (has internal logic capability and runs at 3600/min rate). However, I'd like to present both options, the former being less expensive than the ladder.

[subtle PLC humor intended in previous statement]

Any assistance will be greatly appreciated and returned in kind.

-- John

Last edited by jdcochran; June 8th, 2004 at 04:09 PM.
  Reply With Quote
Old June 8th, 2004, 04:31 PM   #2
elevmike
Member
United States

elevmike is offline
 
elevmike's Avatar
 
Join Date: Feb 2004
Location: Detroit, MI
Posts: 4,012
I'm going to suggest that your two counters, and 6 relays sockets, etc.. are going to cost far more than a small PLC like a Automation Direct DL05 (about $100.00), that has more relays, timers, and counters than I care to count. A simple display (for your counts) like a DV1000 could be plugged directly into port 2 of the PLC. The DL05-DR has a couple of hi-speed inputs also.

The big advantage is that it will be more flexable for the usual necessary adjustments.
  Reply With Quote
Old June 8th, 2004, 05:10 PM   #3
jdcochran
Member
United States

jdcochran is offline
 
jdcochran's Avatar
 
Join Date: Jun 2004
Location: Atlanta GA
Posts: 5
Quote:
Originally posted by elevmike
I'm going to suggest that your two counters, and 6 relays sockets, etc.. are going to cost far more than a small PLC like a Automation Direct DL05 (about $100.00), that has more relays, timers, and counters than I care to count. A simple display (for your counts) like a DV1000 could be plugged directly into port 2 of the PLC. The DL05-DR has a couple of hi-speed inputs also.

The big advantage is that it will be more flexable for the usual necessary adjustments.
Mike -- thanks for the response. The validation considerations are driving the decision to attempt this with a non-programmable solution. Any device that has a programming port is subject to an order of magnitute more complex and expensive set of validation documentaition, testing, revision controls, etc.

Thanks Again,

John
  Reply With Quote
Old June 8th, 2004, 08:20 PM   #4
APB
Member
United States

APB is offline
 
APB's Avatar
 
Join Date: Jan 2004
Location: VT
Posts: 30
By 400-600 clicks per minute I assume you mean number of decisions.
600/60=10 per second. Depending on a number of factors mechanical relays will begin to fail between 1 and 10 million cycles. Add in 6 relays and the probability for failure increases significantly. I think the mechanical relay solution will very quickly have reliability issues.

If programming is out, look into designing a circuit board with old fashioned shift registers, counters, and mosfet output driver.

See if the requirements for validation and revision control can be relaxed if you use something like a PIC or Basic stamp with write once capability
__________________
Andy
  Reply With Quote
Old June 8th, 2004, 09:19 PM   #5
jdcochran
Member
United States

jdcochran is offline
 
jdcochran's Avatar
 
Join Date: Jun 2004
Location: Atlanta GA
Posts: 5
Andy -- very good points.

Thanks,

John
  Reply With Quote
Old September 29th, 2004, 03:49 PM   #6
jdcochran
Member
United States

jdcochran is offline
 
jdcochran's Avatar
 
Join Date: Jun 2004
Location: Atlanta GA
Posts: 5
Project ended up with a PLC anyway. A-B MicroLogix. Designed, fabricated, tested, shipped and commissioned in 3 weeks.

Thanks all for the help.

-- JDC
  Reply With Quote
Old September 29th, 2004, 06:08 PM   #7
Rod
Member
United States

Rod is offline
 
Rod's Avatar
 
Join Date: Jun 2004
Location: Ft Worth, TX
Posts: 535
When relay speed is a concern then I would look to SSR (solid state relay). The cycle time is as fast as a LED.

Rod (the CNC dude)
  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
PC to PLC Protocol TheRixta LIVE PLC Questions And Answers 13 December 17th, 2008 12:56 PM
Need help with AB 1746-HSCE2 High Speed Counter module. SilverLoop LIVE PLC Questions And Answers 4 December 23rd, 2003 08:37 AM
processing speed, PLC joel LIVE PLC Questions And Answers 3 August 9th, 2002 09:41 PM
high speed counter confusion schick LIVE PLC Questions And Answers 6 July 24th, 2002 06:00 PM
"At speed" vs "motor running" input from a VFD ganutenator LIVE PLC Questions And Answers 12 June 10th, 2002 07:28 PM


All times are GMT -5. The time now is 02:37 PM.


.