filtering load cells

[delene]

I have used the PIC18f452 to design a scale - it works great for small scale and weighbridges.
I know want to modify it to weigh cattle.
My problem is that the cattle jumps about - there is never a stable ready. What I want to do is lock the display on the mass of the scale. ie. If you weigh 60kg and jump on the scale after a couple of seconds the scale must lock on 60kg as your weight.

Does anyone have any idea how I go about this.
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This message was ported from CCS's old forum
Original Post ID: 144515804

[Kenny]

:=I have used the PIC18f452 to design a scale - it works great for small scale and weighbridges.
:=I know want to modify it to weigh cattle.
:=My problem is that the cattle jumps about - there is never a stable ready. What I want to do is lock the display on the mass of the scale. ie. If you weigh 60kg and jump on the scale after a couple of seconds the scale must lock on 60kg as your weight.
:=
:=Does anyone have any idea how I go about this.

A very effective method posted by Mr. Hamlett that I have used in similar situations:
<a href="http://www.pic-c.com/forum/general/posts/8286.html" TARGET="_blank">http://www.pic-c.com/forum/general/posts/8286.html</a>

There are others posted on this forum, place 'filter' in the search.

Regards
Kenny
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This message was ported from CCS's old forum
Original Post ID: 144515808

[delene]

Thanks Kenny
I will give it a try and let you know

Delene
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This message was ported from CCS's old forum
Original Post ID: 144515813

[R.J.Hamlett]

:=Thanks Kenny
:=I will give it a try and let you know
:=
:=Delene
I would suggest, that you might need to add a bit of 'intelligence' to the filtering as well. For instance, if you know that the maximum weight that should ever be seen, is a particular value, you could reject any figure above this value (corresponding to a sudden force as an animal jumps), before feeding the numbers into the filter algorithm. You could then have the damping 'assymetric', so that it responds slower to a loss of weight, than to a weight being added, which shouldn't then result in a tendency to 'overweigh' (which would otherwise happen with such an assymetric response. Tuning the algorithm, would be easiest, by having variables holding values for 'upsmall', 'uplarge', 'downsmall', 'downlarge' (corresponding to the points where you change the slope of the damping), and for 'max', 'smalldiv', 'largediv', (the division ratios to be used). If you allow these to be updated externally, using a serial link, you can experiment, to actually see how to get the damping to work best for you. The particular problem you are going to have, is that the 'jump' upwards in value, when an animal steps onto the platform, will be very similar to the jump seen when the animal moves. I would possibly think in terms of turning the damping down, when the platform receives a small duration of signal close to zero (a couple of successive samples), then accepting the first 'high' figure after this (as the animal first jumps on), and then damping more massively from this.
If you have access to a data logger (or could put together some code to do this with the PIC), you might consider getting some typical 'snapshot' raw data sequences, and trying different levels of damping on these in the PC, to see what the best solution is.

Best Wishes
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This message was ported from CCS's old forum
Original Post ID: 144515814

[PCM programmer]

:=I have used the PIC18f452 to design a scale - it works great for small scale and weighbridges.
:=I know want to modify it to weigh cattle.
:=My problem is that the cattle jumps about - there is never a stable ready. What I want to do is lock the display on the mass of the scale. ie. If you weigh 60kg and jump on the scale after a couple of seconds the scale must lock on 60kg as your weight.
:=
:=Does anyone have any idea how I go about this.
----------------------------------------------------

Collect some sample data, and import (or type) it into Excel.
Use the built-in statistical functions, such as AVERAGE or
MEDIAN, etc. to test different filters. You can test other
filters by typing in an equation. Excel can also graph the
results. This is how I proved to myself that a median
filter would work best for my project. A median filter
removes "spikes" from data.
<a href="http://www.pic-c.com/forum/general/posts/13211.html" TARGET="_blank">http://www.pic-c.com/forum/general/posts/13211.html</a>

You can use Excel to model the filter, and test it against
real data. You can see exactly how your PIC program will work,
in advance. And you don't have to buy MatLab. Most people
already have Excel on their PC.

I think the most important thing is to bring the data into
Excel, make a graph of it, and study it. Then you can
decide what filter (or filters) you need.

For lots of discussion articles on using filters with PICs,
go here: <a href="http://groups.google.com/advanced_group_search" TARGET="_blank">http://groups.google.com/advanced_group_search</a>
Set the group for comp.arch.embedded.piclist" and do a search
for: filter
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This message was ported from CCS's old forum
Original Post ID: 144515824

[C Shah]

[quote="delene"]I have used the PIC18f452 to design a scale - it works great for small scale and weighbridges.
I know want to modify it to weigh cattle.
My problem is that the cattle jumps about - there is never a stable ready. What I want to do is lock the display on the mass of the scale. ie. If you weigh 60kg and jump on the scale after a couple of seconds the scale must lock on 60kg as your weight.

Does anyone have any idea how I go about this.
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This message was ported from CCS's old forum
Original Post ID: 144515804[/quote]

I would like to get atleast 18bits of stable ADC data (from 24bit CS5532) connected to loadcell. Also, it should reject all vibrations, other sudden/temporary effects like overhead fan blowing air on it etc... Can anyone help me out on the issue? CPU used in 8051 based core (plenty of ROM+RAM available)!
Thnx
C Shah

[Ttelmah]

If it is an '8051 core', then go and ask on a group for this. This group is for people usng _CCS C_, on the PIC processor.

Best Wishes

[Shah]

[SherpaDoug]

I want to second the idea that you log some data to a PC and play with it using a spreadsheet or other good math modeling tools. Once you figure out what works you can then figure out how to do it in a microprocessor. It is probably going to be more than just averagings. Try googling "Median Filter" or searching for "olymipc scoring" on this forum.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[Ttelmah]