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
Unread November 28th, 2004, 09:34 PM   #1
TEOWK
Member
Malaysia

TEOWK is offline
 
Join Date: Oct 2004
Location: Batu Pahat
Posts: 38
Load Cell Application

Dear All,
I am working with a Load Cell project. The auto packaging machine will weigh the product for 15kg. When 15kg is reached, the dough input will stop and the 15kg dough is then packed.

For this application, can we connect the load cell directly to a Analogue to digital converter, and use the PLC the control its I/).

Right here we have a digital scale CAS Model No: CI 5200A. Shall we use the load cell with this scale, and then obtain the signal from this scale to control the dough output motion?
Thanks
  Reply With Quote
Unread November 28th, 2004, 09:44 PM   #2
elevmike
Member
United States

elevmike is offline
 
elevmike's Avatar
 
Join Date: Feb 2004
Location: Detroit, MI
Posts: 4,012
It seem the model number is not for the scale but for the display.. Try contacting the manufacture of the scale to see if they have an interface for it. http://www.cas-usa.com/contact.htm

By they way you didnt mention the PLC brand and model either.. I have now Idea as to your PLCs capabilities without knowing what it is.
  Reply With Quote
Unread November 28th, 2004, 09:51 PM   #3
TEOWK
Member
Malaysia

TEOWK is offline
 
Join Date: Oct 2004
Location: Batu Pahat
Posts: 38
Thanks for your reply.
I intend the use the Matsu****a NAIS FP0 with a FP A/D unit to obtain the analogue signal from load cell. For the user interface, I am thinking of using Taiwan HITECH touch Screen to key in the 15kg into the PLC.
Thank you.
  Reply With Quote
Unread November 29th, 2004, 12:51 AM   #4
rsdoran
Lifetime Supporting Member
United States

rsdoran is offline
 
rsdoran's Avatar
 
Join Date: Apr 2002
Location: Birmingham, AL
Posts: 7,372
cant say **** here..ie s h i t even in the name M a s u s h i t a.

You have at least 2 choices
1. Interface the scale (RS232 etc) to communicate to the NAIS plc.
2. Use the scale to send a "weight reached" signal to the plc.

The first choice would offer more resolution and precision.
__________________
http://www.patchn.com Industrial Electrical & Maintenance @ www.patchn.com "Tell me and I forget, show me and I remember, involve me and I understand."
  Reply With Quote
Unread November 29th, 2004, 04:09 AM   #5
JesperMP
Lifetime Supporting Member + Moderator
Denmark

JesperMP is offline
 
JesperMP's Avatar
 
Join Date: Feb 2003
Location: Copenhagen.
Posts: 14,002
I dont know the weighing device you are using. But I do have some general tips.
If you are considering to let the PLC handle the weighing by means of the raw signal from the scale then there are several things that you must consider.

First, how do you get the value from the loadcell into your PLC.
Alternatives:
1. Take the signal via a loadcell transmitter. It can be 0-10V or 4-20mA.
2. Install a loadcell module in the PLC. Connect the loadcell directly to the module.
3. Read the value via Profibus or Devicenet (if possible).
4. Read the value via serial ASCII (if possible).

Second you must do two things that a weighing device will do for you:
1. Tare the signal when you start the weighing sequence.
2. Memorize the "tail" from the previous weighing sequence. Then stop the weighing before the setpoint is reached by taking the tail into account.
__________________
Jesper
See my profile interests for Q&A
  Reply With Quote
Unread November 29th, 2004, 04:53 AM   #6
sandymax
Member
India

sandymax is offline
 
sandymax's Avatar
 
Join Date: Nov 2004
Location: India
Posts: 112
AND 4401

Hi,
i have exp in weighing machine.
i prepfer to have a AND 4329 or 4401 weighing controoler
it is having so many features like recipe etc.
i did one application in which i use PLC siemens 221 micro
and AND 4329
i put seppoints
i.e final 25 KG
preliminar 20 kg
and taken as input to PLC based on thease inputs i control Valve
so i am having good results even you set free fall , zero band

Thanks
sandy
  Reply With Quote
Unread November 29th, 2004, 08:21 AM   #7
elevmike
Member
United States

elevmike is offline
 
elevmike's Avatar
 
Join Date: Feb 2004
Location: Detroit, MI
Posts: 4,012
Update:

A good friend of mine just told me that most large industrial scales have a programmable setpoint to activeate a form C relay output when the scale has reached the setpoint. Sound pretty simple.. Check with the scale company.
  Reply With Quote
Unread November 29th, 2004, 08:39 AM   #8
mordred
Member
Canada

mordred is offline
 
mordred's Avatar
 
Join Date: Mar 2004
Location: Red Deer
Posts: 1,892
A cheaper solution is to purchase a 920i weigh scale indicator. This indicator is fully programmable with optional input/output cards. The reasons I suggest this route is the simplicity in maintaining calibration. Also in many applications, weights and measures has a few regulations that straight PLC to load cell connections would have difficulty in following. However it does not sound like your application would require certification. Another two options are GSE series scales or Bizerba scales are also programmable and reliable. In our plant we have a GSE 650 talking to an Omron PLC via constant transmit ascii strings of the weights as they pass through the scale. This in turn selects which chute to kick off at.
__________________
Can I ground short a Sparky?

Last edited by mordred; November 29th, 2004 at 08:42 AM.
  Reply With Quote
Unread November 29th, 2004, 12:30 PM   #9
Laurent
Member
Canada

Laurent is offline
 
Laurent's Avatar
 
Join Date: Jul 2002
Location: Montreal
Posts: 110
Hi TEOWK,

For a FP0 analog input you will need a load cell signal conditioner. Those components may be adjusted by their manufacturers in order to fit your requirements (output signal, range, span...). Your best choice for the FP0 would be to deal with a 0-20mA signal (12 bits/4000 pts fully usable in current mode).

Carefully consider the second advice from JesperMP: this is key in weighing solutions to have the system "auto-teaching" its own inaccuracy in order to correct the target value for the following shot. This may not be properly achieved in a serial communication (but this actually depends on your process speed and targetted accuracy).

By the way I am currently working on dough depositors. What kind of system are you dealing with?

Laurent
  Reply With Quote
Unread November 30th, 2004, 07:41 PM   #10
TEOWK
Member
Malaysia

TEOWK is offline
 
Join Date: Oct 2004
Location: Batu Pahat
Posts: 38
Thank you.

I just met with the customer yesterday. They would like to weigh the concrete cement and pack this product into 15 kg each. There is an old weighing indicator kept by them. The brand is CAS CI 5200A. I took this weighing indicator and test with a load cell yesterday.

The weighing indicator has built in relay for HIGH, LOW and FINAL setpoint. However, when I connect it to a load cell, error message "no LC" and "OVER" keep pops out. The signal line carries 0.8mV when I aded a load. I am trying to figure out this problem.

Thanks again to everyone.
  Reply With Quote
Unread November 30th, 2004, 08:18 PM   #11
Terry Woods
Member
United States

Terry Woods is offline
 
Join Date: Apr 2002
Posts: 3,170
"No LC" sounds like an open circuit.

"OVER" sounds like a short-circuit.

If the signal line carries 0.8V with any load, small or large, then that sounds like... a defective A/D converter?

Check the wiring between the Load Cell and the Reader first.

Then, if that is good, use a different analog input location or, if you don't have another location to use, replace the A/D converter.

However... before doing any of that stuff... if your Load Cell is subject to a "SCALER ROUTINE" then be damned sure to check the operating points in the "Scaler Routine" first.
  Reply With Quote
Unread November 30th, 2004, 09:46 PM   #12
TEOWK
Member
Malaysia

TEOWK is offline
 
Join Date: Oct 2004
Location: Batu Pahat
Posts: 38
The load cell gave output between 0.1mV to 0.8mV when I imposed a different load on it. Ii seems that the load cell is O.K. But then, could i be the parameter setting problem in the weighing indicator. Is the SCALER ROUTINE a parameter(Function) in the indicator?
Thanks.
  Reply With Quote
Unread December 1st, 2004, 03:10 AM   #13
JesperMP
Lifetime Supporting Member + Moderator
Denmark

JesperMP is offline
 
JesperMP's Avatar
 
Join Date: Feb 2003
Location: Copenhagen.
Posts: 14,002
This is an example of a POSSIBLE functionality of the three signals from your weighing device.
Its just to give you an idea. Study the documentation to find out exactly what the signals mean.
Note: Because there is a HI and a FINAL signal, I am guessing that the weighing sequence require a coarse and a fine dosing speed.
This can be achieved by running a screw feeder at varying speeds, or by having two screw feeders - big + small.

Weighed up. Stop adding material.
FINAL ON
HI ON
LO OFF

Nearing the setpoint. Only use "fine" dosing.
FINAL OFF
HI ON
LO OFF

Far from the setpoint. Add material with "coarse" dosing.
Or when emptying: Not empty.
FINAL OFF
HI OFF
LO OFF

Tared and empty.
Or when emptying: Emptying finished.
FINAL OFF
HI OFF
LO ON

__________________
Jesper
See my profile interests for Q&A
  Reply With Quote
Unread December 2nd, 2004, 08:32 AM   #14
dandrade
Member
Brazil

dandrade is offline
 
Join Date: Jan 2004
Posts: 374
Quote:
For this application, can we connect the load cell directly to a Analogue to digital converter, and use the PLC the control its I

The load cell gave output between 0.1mV to 0.8mV when I imposed a different load on it.
It is sure that to impedance of the cell and input they are adequate?
Modules (interface) manuals, indicate options of extremely short signals (less mV, mA)
For me, it incorrect load cell directly to a Analogue input PLC.Confirm, guys?
  Reply With Quote
Unread December 2nd, 2004, 08:48 AM   #15
mordred
Member
Canada

mordred is offline
 
mordred's Avatar
 
Join Date: Mar 2004
Location: Red Deer
Posts: 1,892
no LC is usually no load cell. the over is the MV|VO reading is too high or out of range of Full scale which should be s asetting in your parameters. You either have a bad load cell or you have a bad indicator a\d converter.
  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
VFD , motor , PLC (start /stop/position application) Gautham LIVE PLC Questions And Answers 28 May 25th, 2006 05:29 PM
How to calibrate a load cell & how to program mitsubishi plc for analog input M. HASSAN LIVE PLC Questions And Answers 7 February 24th, 2005 11:53 AM
How to calibrate a load cell & how to program mitsubishi plc for analog input M. HASSAN LIVE PLC Questions And Answers 1 February 19th, 2005 07:10 AM
Load Cell and 1746-NR4 Mark Buskell LIVE PLC Questions And Answers 10 July 12th, 2004 05:51 AM


All times are GMT -5. The time now is 05:27 AM.


.