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Stefan Kanev
10/30/11 14:14
Read: 564 times
Silistra
Bulgaria


 
#184457 - some Q/A
Responding to: Zeeshan Ashraf's previous message
My friend was having a lot of variance batch-to-batch - this was one problem


how big was variance and what precision was achieved by system?


Hopper dead weight = 250 ~ 300 KGs
Load-cells on hopper = 3
Load cell specs :
Type = Tension S-type
Capacity = 500 KG each
Output type = 2mV/V
Connection = 6-wire (EX+, Sense+, x-, Sense-, Out+, Out-) with sheild.
Total measuring range = 1000 ~ 1500 KGs
Minimum weight to measure = 0.1KG
Accuracy = +/-10% approx that of min. resolution

So total max weight is 1800 kg with 3 loadcels x 500 kg each.
Loadcells here are undersized, i suppose they are out of health already.
'Legal' trade accuracy with 'standard' C3 loadcells(3x500 kg capacity) is 0.5 kg, in best case - 0.250 kg . This is something what Your friend should be informed about. So recipes/batches should be developed with these limitations in mind - do not lie Yourself and friend that 0.1 kg accuracy is realistic aim. You can achieve such result (0.1kg) but You can't declare it.

In the modular concept, theoretically, if a single channel fails, only that particular channel module needs to be replaced. This reduces long-term costs and re-calibration time.


If one amp-channel fails, You still will need recalibration with test weights on hopper. Or individual loadcell+amp calibration on test place with test weights (not whole hopper).And here we go to 'digital load cell'.
You can buy new set with new digital loadcells and replace old cells.
In case of fail You will change D-loadcell. Recalibration will be not needed, but price will be high. Or You can DIY D-loadcells.

With 3-4 standard loadcells - passive summing box and AD7730 is enough.
There is no need of amp-boards. Main reason for using amp-boards are 2:
- noise on cable , between loadcells and PLC
- PLC's ADC usually are 'universal' , 12...14 bits.
AD7730 (and other in this class) eliminates amp-need.
Multi-channel amplifier/multi-amplifier box - is not needed in Your system.
Multi- ADC system is good only if You can use:
- reliable loadcells with reliable REALISTIC data in passport( Loadcell's passport data / test report by producer)- test report can be used instead test weight.

or

- test weight to calibrate single loadcell- disconneced from hopper .


Think about temperature changes on loadcell's output too.
Check datasheets with care.

regards

List of 58 messages in thread
TopicAuthorDate
Load-cell conditioning / summing      Zeeshan Ashraf      10/29/11 10:29      
   what is that?      Erik Malund      10/29/11 15:43      
      RE: #184430 - what is that?      Zeeshan Ashraf      10/29/11 15:45      
         then say what you mean      Erik Malund      10/29/11 15:53      
            your description leaves something unclear      Erik Malund      10/29/11 16:02      
               RE: #184435 - your description leaves something unclear      Zeeshan Ashraf      10/29/11 16:27      
                  where are the loadcells???      Erik Malund      10/30/11 06:08      
                     RE:      Zeeshan Ashraf      10/30/11 09:01      
      RE: #184430 - what is that?      Zeeshan Ashraf      10/29/11 15:56      
         some Q/A      Stefan KAnev      10/30/11 14:14      
            RE      Zeeshan Ashraf      10/30/11 15:27      
               Q/A 2      Stefan KAnev      10/31/11 03:00      
                  RE      Zeeshan Ashraf      10/31/11 04:18      
                     re re      Stefan KAnev      10/31/11 05:00      
                     get rid of that summing amp      Erik Malund      10/31/11 07:09      
               you will be lucky to get 16 bits      Erik Malund      10/31/11 07:04      
                  Precision again...      Kai Klaas      10/31/11 16:58      
                     Comparison      Per Westermark      11/01/11 01:12      
                     RE      Zeeshan Ashraf      11/01/11 02:20      
                        why do you keep babbling about a summing amp      Erik Malund      11/01/11 06:41      
                        Priorities...        Kai Klaas      11/01/11 07:07      
                           RE      Zeeshan Ashraf      11/01/11 07:45      
                              cirrus, ti      Stefan KAnev      11/01/11 08:42      
                                 maxim, linear tech, Analog Devices      Erik Malund      11/01/11 10:09      
                                 RE      Zeeshan Ashraf      11/01/11 17:36      
                              it takes the same time ...      Erik Malund      11/01/11 10:14      
               500 running foot of cable      Stefan KAnev      11/01/11 22:25      
                  RE      Zeeshan Ashraf      11/01/11 22:57      
                     Go for ADC with multiplexed inputs instead of multiple ADC        Per Westermark      11/02/11 07:14      
                        Good Advice      Michael Karas      11/02/11 08:00      
                           It depends...      Kai Klaas      11/02/11 08:48      
                              This is a MODULAR concept !      Zeeshan Ashraf      11/02/11 19:57      
                                 it depends      Stefan KAnev      11/03/11 00:50      
                                 don't be ridiculous      Erik Malund      11/03/11 07:17      
                                    Consider other parameters too.      Zeeshan Ashraf      11/03/11 08:16      
                                       calibration      Stefan KAnev      11/03/11 08:46      
                                       if you do not buy bootleg parts ...      Erik Malund      11/03/11 08:50      
                                          Voltage reference      Per Westermark      11/03/11 09:08      
            Accuracy...      Kai Klaas      10/30/11 16:40      
               RE      Zeeshan Ashraf      10/30/11 16:55      
                  Keep the signal paths as simple as possible.      Michael Karas      10/30/11 20:34      
                  sun umbrella      Stefan KAnev      10/31/11 03:10      
   Separate Gain Paths - Not The Best      Michael Karas      10/29/11 23:33      
      RE: #184439 - Separate Gain Paths - Not The Best      Zeeshan Ashraf      10/30/11 00:11      
         Error Budget Calculations?      Michael Karas      10/30/11 09:50      
            Hysteresis      Kai Klaas      10/30/11 10:14      
         This should alarm you!      Kai Klaas      10/30/11 09:58      
            RE      Zeeshan Ashraf      10/30/11 10:14      
               No contradiction...      Kai Klaas      10/30/11 10:22      
                  RE      Zeeshan Ashraf      10/30/11 10:40      
                     Digital Summing        Michael Karas      10/30/11 12:55      
               with DC exitacion ...      Erik Malund      10/31/11 07:20      
            welcome on board      Erik Malund      10/31/11 07:14      
      RE:      Zeeshan Ashraf      10/30/11 00:16      
   Look at ADuC845      Oliver Sedlacek      10/31/11 01:44      
      ADuC845      Russell Bull      11/16/11 20:54      
         Noise V good      Oliver Sedlacek      11/17/11 04:39      
            Ok, then      Erik Malund      11/17/11 06:26      

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