Checking Sugar level in berries

I am using an old conveyor that has a couple load cells. It has one load cell on each side and weighs about one foot of conveyor space. There is a fancy controller to calculate the weight that is broken. I am not sure what the mathamatical equasion is to calculate the moveing weight. I know I will be using the belt rpm and the moving anolog signal. I am putting sugar in berries. The ratio of sugar is one part sugar and four parts berry. I know I have other parts to put in my program like the changing sugar level in the berry, however, I need to figure out the math equation. Any help would be great. I have no problem writing a program, I just havent been able to see all the variables.I am going to use a plc insted of their broken expensive controller.

Thanks Rick

Hi rabristol,

Can you post additional info, such as -

Which PLC are you using?

What is the avg. line speed?

How/where are the sugar and berries combined?

Is the sugar weighed out on the same load cells as the berries, by another scale or metered out by auger?

By what means are you bringing in the weight data in to the PLC (analog, RS-232, etc.)

Any additional info on the system could be of help.

For the most part, and this is overly simplified, take the sampled weight value and multiply it by 0.25, then take that value to use for the amount of sugar to add, i.e. a time sampled weight of 4 pounds of berries, when multiplied by 0.25 would result in 1 pound of sugar needed to be added (as in your 4 part berries to 1 part sugar spec.)

rabristol,

Your calculation is probably just as easy as you might think. I have not had to do this for a long, long time, but here is what I think I remember:

To use this method, you need to plan to capture and sum together a running quantity of Sample Weights that will be taken on regular Sample Times.

You need variables:
D = Distance between loadcells (inches) - this is the physical measurement of the centerline distance between each loadcell roller. Be as accurate as you can.
S = Speed of the belt (inches per minute)
W = Sum of Sample Weight (pounds) - the weight taken from the input from the combined loadcells with the dead weight of the belt taken out.
T = Total Sample Time (seconds) - the period of time between each sample weight measurement.
K = Number of Sample Weights taken

Your running weight (or pounds per second) is

( W x D x 60 ) / ( K x T x S )

Explanation: Each time you take an individual reading, you are measuring the total weight on the belt section between the two loadcells. While the belt runs and you take multiple, regularly timed readings and, then, by knowing the speed of the belt and the accumulated weight and this distance, you can calculate a running average pounds per second going by on the belt. Knowing this, you can calculate the feed rate of you sugar in pounds per second (or whatever the correct units are) to meet your blending requirements.

Steve

One more thing...

To calibrate and check your maths you will need a calibration chain.

Its just a chain. You could rent some.

We do this with 100 feet chains. After it has passed through the system... check the results... you've already weighted the chain!

You should be programming some damping function for the vibration of the conveyor could misled you. We usualy Zero the sytem, running it empty and taking out the vibes with math... Ready to use systems will have this incorporated in there electronics.

first make a table by just trial and error.
so use a pulser on the belt that will give you the speed.
on every pulse get the analog value. put it in a add register.
every second read the register and zero it again. then you have the amount of analog each second. in the table you can find the weight of product.
it will not be nice linear i think.
if it is well then it can be done without a table.
To refine the program a timer and a bucketregister can be used.
For mixing cement it is used much. There is one belt running along some bunkers.
If the belt runs at same speed a simple analog calc is enough. as the analog value from the load cells can be directly converted to the sugar valve.