New.. and confused about load cells & pressure transmitters ohm's

[SABorn]

Well guys as far as i am aware it is not a recommended practice to post ones phone number to the forum, and hence the PM.

I did have a chat with Paul on the dog and bone to sortout some finer details and establish if he was keen to have a go at this and his level of ability, as you would know it is far easier to talk direct rather than playing a forum tennis match of questions.

It is nice to know there is a interest in this project, and for your benifit i will endeaver to keep this in the public arena.
Bare in mind this is Pauls project so he really has the final say of what goes public, but i look to be doing the design of this (how did that happen?) so i have some say as well.

My understanding is Bryan is also doing a version of this but with a commercial interest, i am a little different where i rather do things on a public level so the OP can learn and others can see what develops as well.

Project updata..........

Where this looks to be heading.

The display will be a standard lcd 2 line 40 charactors, just to keep it simple and low cost.

The picaxe will be a 20x2 and drive the lcd direct off the outputs, this leaves heaps of I/O's for other tasks

The front panel will have 3 press buttons for system control
1 Button for tare
2 buttons for menu selection

The calibration values will be set from the menu buttons, press both buttons to enter calibration, press tare to select Cal1 or Cal2, use the menu buttons to increase or decrease the calibration value, press both buttons to write the value to eeprom and exit calibration, repeat the process for Cal2.

The reason for 2 calibrations is Paul wants to use this in a loader and a forklift, each will have its own calibration.

Press the menu button to select ...Loader or Forklift

Lift the bucket/forks to a determined point and press Tare

Tare will write the present sensor value to eeprom, each and every sensor reading there after will have the Tare value subtracted from it, leaving the difference in value above tare (weight value) the weight value will then be divided by the calibration value entered, to give a value in Kgs, this is then written to the display and the process repeats.

Some option considered........

To use 1 menu button as a "weigh" button so a weight is only taken when the button is pressed, this way the weight will be locked on the screen untill the button is pressed again

If the weight button is used then a running total can be done, but this would require a further button press to add the weight, otherwise if several weight readings was done of the same load it would be added to the total giving garbage information.

As its a 2 line display the total could be on the second line.

Originally i designed the board with a 15 volt reg for the sensor supply, but then realized the loader is 24volt and the fork is 12volt so the reg wont work.

The type of sensor to be used is yet to be determined and can only hope the input voltage range dont effect its reading, as a direct supply of system volts will not be a stable input voltage.

Should resolution be very poor and non workable with the signal fed direct to the picaxe than i have allowed on the pcb for a ADC to 16 bit converter to be added up front to increase resolution from 1024 to 65535 for 0 to 5volt sensor input.

More as this develops.......

Pete.

 

[paulmac]

Pete,

Sound good. I like the idea of buttons instead on trimpots. Makes it much more user friendly. If you use the (1) menu button as the tare button, could you not use the other 2 buttons for;
(2) record/add weight and
(3) subtract/clear weight?

So when you press button (2) the current weight is added to the total.
When you press button (3) the current weight is subtracted from the total(allows you to 'fix' a double press etc)
When button (3) is held for say 3 seconds it clears the total.

Regards

Paul

 

[SABorn]

New update on progress..........

The project has advance nicely, thus far and much has been sorted and working.

I have opted to host more detailed information of this project on a different forum, and before a few start to jump up and down that i have taken this off forum, let me explain.

Firstly i did not like the comments from a very small minority here of me speaking with Paul by phone.
As Admin has cleaned up the thread i will continue to post here.

Secondly should the moderators of ET dont like my work and would rather that Picaxe projects not be disscussed on this forum than they can simply delete the links that i will provide, this way i have control of my work and it can not be deleted from the forum.

Thirdly i can post in article form on the host forum with photos and code inserts which is easier for me.

This is of no way intended to remove this thread from this present forum and i will link this thread to any further updates posted, as well as discuss the project here as well, so dont feel the need to discuss it on the other forum, its only a viewing platform.

If ET admin is unhappy with this approach than please advise and i will not continue.

Update can be found here...........

**broken link removed**


Pete.

 

[SABorn]

Pete,

Sound good. I like the idea of buttons instead on trimpots. Makes it much more user friendly. If you use the (1) menu button as the tare button, could you not use the other 2 buttons for;
(2) record/add weight and
(3) subtract/clear weight?

So when you press button (2) the current weight is added to the total.
When you press button (3) the current weight is subtracted from the total(allows you to 'fix' a double press etc)
When button (3) is held for say 3 seconds it clears the total.

Regards

Paul

Yes all of what you asked can be done, and the current version has most of that except for the subtract a weight function, which i will give some thought to.
There is a much more in depth explanation of the present functions in the update i posted a link to.

Pete.

 

[bryan1]

G'day Paul,
Between Eric and myself the glcd code is just about sorted and hopefully this weekend I'll design up and make a circuitboard and then simulate the 1-6 volts in real time. Soon I'll get some of those IP68 box's and make them up then test each of them out in the weather along with a sealed moisture circuit to see if any moisture finds it's way into the sealed box's.

Regards Bryan

 

[paulmac]

To All,

I have spoken to both Bryan and Pete via phone, for the simple reason that it's a lot easier to explain the idea and discuss details in person. Both have been very keen and helpful and have posted details on what was discussed on this forum. It's got the project up and running much quicker.

Pete, I've had a look at the post and it looks great. I like the 2 line display.

Bryan, sounds like you and Eric are flying along. Hopefully the transducers will arrive soon.

regards

Paul

 

[Reloadron]

I should know this but what was the final display? Also the final transducer decided on?

Ron

 

[SABorn]

From my understanding Bryan is building a unit to a commercial standard and using a dot matrix display.

My objective is slightly different and am desiging a unit to a lesser standard that can be constructed by any home electronic tinker with basic off the shelf components of a lower price bracket and without the need for pic programmers and a knowledge of writing code etc, as i intend to post the final code used so anyone can dump it into a picaxe chip.

The display i am using is a standard 2 line 16 character LCD, the cheap crappy type of which of just purchased 10 of these.........

**broken link removed**

The sensor we agreed to try was this one................

**broken link removed**

which was the 1 to 6 volt output and the cheaper of the range looked at, a sensor in the 3000 psi range should be enough.

Pete.

 

[paulmac]

Ron,

Because of the cost (~$40) both are using the ebay transducer with 1-6v output and 400bar range. Pete is using a standard 16 character 2 line lcd display and Bryan is using a 128x64 glcd

Regards

Paul

DAMN!... you beat me! Must type FASTER!

 

[Reloadron]

Thanks guys. Yes, I noticed all you guys from down under are quick on the keyboards.

You also keep strange hours.

Ron

 

[SABorn]

You also keep strange hours.

How did you know my wife was called Hours, and who you calling strange.

We are all too poor here from spending our money on electronics to buy a watch or a clock so we dont know the time.

Besides that big hand, little hand thing is just confusing for me.

Pete.

 

[SABorn]

I have updated the thread with a schematic and some other small progress reports, for those who are interested it can be found here........

**broken link removed**

Pete.

 

[Reloadron]

Nice find on the pressure source.

Really nice job on the link too Pete. Like, wow!

Ron

 

[SABorn]

While talking to a friend on the phone and discussing problems he was having with a Weight Master Totaliser scales on a tractor loader he has, i searched the net for data on this equipment and in the data sheet i noticed their sensor on the loader arms had 2 targets or trigger sensors as they called it.

The reason for this was a weight reading would only be taken if the arms was being lifted up and no reading was taken in a downward movement, as the pressure is different depending on the direction of travel.

This also allowed for the speed of travel to be assessed as well, and only steady even movement recorded a weight reading, increasing accuracy of the readings.

My question now is do anyone think this is an important factor and should i increase the Trigger Sensors to 2 and implement this in code to only read in one direction of travel.


First i thought it was just more wiring needed to do this, but if you have to run a cable of 2 wires than its no harder to run a cable of 3 wires.



The page from the data sheet is attached below.

Pete.

 

[Reloadron]

The reason for this was a weight reading would only be taken if the arms was being lifted up and no reading was taken in a downward movement, as the pressure is different depending on the direction of travel.

That makes sense to me. The pressure on the ram when lifting would be the pressure required to lift the load and a representation of the load weight I would think. On downward movement the ram pressure would be bleeding off. That would be my guess as it makes sense to me.

Ron

 

[paulmac]

Pete,

Just read your post, there's a few points here.

1. The Basic or entry level scales don't use the multiple trigger points, weigh while lifting, moving etc. Just a static weight at a fixed point, even to the end of having the loader stationary. This is the only way to get an accurate weight with JUST the pressure transducer.

2. Advanced scales (and expensive ones!) will use angle sensors, position sensors and sensors that measure the speed of the bucket movement to allow weighing without stopping the lifting or forward motion of the loader, so that they can remove all the variables from the measured weight.

I have spent quite a bit of time with various suppliers asking how their systems work and even getting demonstrations at various field days. The Advanced scales are great, but cost $3000 and up and are overly complicated for the original idea I had.

Trying to measure with the rams in motion, with just the pressure transducer would be almost impossible because any changes in engine rpm, forward speed and the amount you pulled back on the value control would ALL affect the oil flow rate to the ram and therefore the pressure in the ram. The more oil flow to the ram the faster it will lift, the more force is needed to overcome the inertia of the weight in the bucket, the higher the pressure and visa versa . You would get a different pressure reading for the same weight, depending on the variables mentioned above.

Having a second trigger point wouldn't be a bad thing for any machines that are difficult to fit a mechanical sight point too, but I think, having spoken to scale suppliers, there's not any other way to weigh the load other than a static point with just a pressure transducer.

Regards

Paul

 

[SABorn]

I added some photos of the prototype board and basic setup to date, should anyone be interested, it can be viewed here...............

**broken link removed**

Still waiting on the sensors to arrive before i can do much more to the project.

Will keep you all updated as things develop further.

Pete.

 

[Reloadron]

Just plain wow! Pete, you took this to a whole new level. Really nice work you have done there. Did I ever ask if you were retired?

Ron

 

[SABorn]

Thanks for the kind comments Ron.

Retired.......Hmmm, i wish, working on it as only about 20 years to go, and counting......


Pete.

 

[SABorn]

Another progress update, can be found here................

**broken link removed**

I intend to do a few circuit changes for the end project like add a piezo to indicate when the arms are on target for a weight reading, and shuffle a few sockets etc around for better access, otherwise it is close to complete should final testing prove it all works accordingly.

Waiting on sensors now.

Pete.