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

[ericgibbs]

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.

hi Pete,
Did you finally sort out the ADS1100.?? the d/s is a little 'naff' on certain points.

 

[SABorn]

Hi Eric,

Yes i did get the ADS1100 working rather well, and think it is an excellent chip, but have been reserved to post much information on the ADS1100 setup as i am waiting to have a sensor to test it out, and to prove i have it all sorted correctly.

I see little point in quoting a full setup procedure to find it dont work with the sensor.

Are you and Bryan intending to use the ADS1100 as a front end to the sensor as well. ?

I am happy to share what i found if anyone cares to ask me, otherwise i will post full details once all is proven to work correctly.

The data sheet is correct and the information is all there, its just a little hard to put it all together to get the full 16 bits from a single input.

Pete.

 

[ericgibbs]

hi Pete,
I'm not sure what Bryan is using for his scale, I only helped with the Glcd.??

I use the ADS1100 in 16bit 8smps mode, differential and single input, with a PIC for general purpose measurement projects.
Eric

 

[SABorn]

Eric,

The ADS1100 only works between 0-3 volts on a single input, and it was only after i had tested it that i found this quoted in the data sheet.
This limits the full scale reading to 8 bits for a single input, which was not what i was wanting.

I did find a way around this with circuit changes and coding, but need to prove it all works correctly with a sensor before i go quoting a sure fix.

One question you might be able to answer, is why when i read location zero the bit value is twice the value of location 1.

Why would location 1 be half the value and for what reason would you use it for.

Pete.

 

[ericgibbs]

Eric,

The ADS1100 only works between 0-3 volts on a single input, and it was only after i had tested it that i found this quoted in the data sheet.
This limits the full scale reading to 8 bits for a single input, which was not what i was wanting.

I did find a way around this with circuit changes and coding, but need to prove it all works correctly with a sensor before i go quoting a sure fix.

One question you might be able to answer, is why when i read location zero the bit value is twice the value of location 1.

Why would location 1 be half the value and for what reason would you use it for.

Pete.

hi Pete,
At 8 smps, the ADS1100 accept a single input from 0v thru +5V, but you will only get 32768 ie 15Bit, when using a Gain of 1.

Again with a Gain of 1, for a differential input, at 8smps it will accept +/-2.5V, this gives the full 16bit.... 32768 below ie: negative and 32768 above ie positive.

EDIT:
I guess you know that you address the ADS then do two successive reads, high byte, low byte.??

 

[ericgibbs]

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

hi Paul,
Have the transducers arrived yet.?

 

[paulmac]

Eric and Bryan,

Yep, they have, but I've started seeding so haven't had the time to post them on. Hopefully Monday.

 

[SABorn]

Post advertising another site deleted - please take note that this site isn't for promoting your own site.

Consider this a final warning as you have already been warned about this behaviour before!

Moderator.

 

[paulmac]

Bryan,

Sorry for not catching up with you sooner. Seeding has finally started and things get a bit hectic. The transducers have turned up and as Pete is building one too now, I'll send 1 to each of you to have a play with. Can you let me know your postal address and I send it, hopefully tomorrow. I tried to PM you but said you're inbox was full.

Need sleep, catch up with you later.

Regards

Paul

 

[SABorn]

I have received the sensor and done some tests.
I posted an update on the other forum but if i link it to here Nigel will ban me.

( let me just say i have no problems with the rules and if i had been politely advised that linking to other forums was not allowed, than the need for a RED notice could have been avoided, and for the record... no i was not warned before,..... as well it is not my site, i only help out with admin duties as many here do help with moderator duties)

Anyways.......... here is the update..........

I had done some tests on the pressure sensor on the bench here, and got some not exactly linear readings, the gauge used was unknown if it was true and correct.
So today i had a little time to visit a friend of mine who owns a hydraulic workshop, and use his test bench to run some better controlled tests.

Very happy with the results and got good linear readings across the full tested scale ( 0 to 3000psi) as the test bench was setup for a max of 3000psi the testing was limited to this, as to adjust the bench for higher pressures required some changes to be made and seen no point in needing to go higher, secondly i was a guest in the workshop and did not want to exceed the kind free use of the equipment.

With no pressure the display showed a reading (no recorded) this was zeroed with Tare.
The pressure was increased in steps of 250psi from a start point of 500psi, the gauge used was a large analog pressure gauge that allowed a little room for error, but close enough to prove the results.
The readings were rounder off.

Recorded results

500psi 5000 adc
750psi 7500 adc
1000psi 10000 adc
1250psi 12500 adc
1500psi 15100 adc
1750psi 17700 adc
2000psi 20500 adc
2250psi 23200 adc
2500psi 26000 adc
2750 psi 28100 adc
3000psi 31200 adc

The test was repeated several times with slight differences in readings, this was mainly due to the analog pressure gauge and the ability to align the needle with accuracy.
(or should i say the person controlling the pressure and the lack of understaning on need for accuracy, and a attitude of near enough is good enough)

A calibration factor was entered of 100:1 and the test repeated, the display showed corresponding readings to the pressure applied.

At a guess i am expecting 3000psi to be equal to a maximum weight of 5000 kg, and think the resolution of the readings should give reasonable display results within the 50kg range Paul had wanted.

Should anyone be interested the thread on the sensor is..... Square BSPP 1/4 inch.

Gerald had made several recommendations to the mounting of the sensor, as he had commented it is common for farmers to kill the sensors due to the hydraulic hammer effect applied to the sensors.
This is mainly due to operating equipment on rough ground with the bucket arms raised, and the hammering the hydraulics get from the arms bouncing up and down.

He recommends installing a ball valve under the sensor and shutting the oil flow off when the weight indicator is not required.
Also fitting the sensor on a small hose or tube and not directly into a large hose or tee fitting as this helps to dampen the shock effect.

And the last recommendation is to fit a gauge saver prior to the sensor or use a fitting that has been welded up and with a small weep hole for the oil to squeeze through, as this restricts the huge surge of oil to the sensor with hammering that destroys them.

All good advice i think.

Now it just a matter of Paul finishing his crop sowing and some spare time to install the system, then do some field testing to prove it all works within the equipment.

Pete.