hi k,
screen aka shield.
The signal level from the L/C is very low, which means the INA has to have a high gain.
So any 'electrical' noise that is picked up on the L/C wires, will give a 'noisy' Vout signal.
Grounding the screen/shield to 0v/common will shield the L/C cable from pick up electrical noise.

Solder a a short piece of bread board type wire to the screen and poke it into the B/B 0v line.
Note: the 100R for Rgain.

Personally I would chose to use pin #15 which is 5V rather than pin #14 which is only 2.5v, this will increase the L/C output voltage by 2.
E

 

"The signal level from the L/C is very low, which means the INA has to have a high gain.
So any 'electrical' noise that is picked up on the L/C wires, will give a 'noisy' Vout signal.
Grounding the screen/shield to 0v/common will shield the L/C cable from pick up electrical noise."

Great explanation!

 

Hello eric!

I tested as you advised in post #19

No force on the L/C 57mV
As I increased force, it went up to 75mV *and it saturated at this value.

The new L/C came in, its a very cheap load cell that can only take 10Kg, link : https://www.amazon.com/a14071900ux0057-Aluminium-Electronic-Weighting-Replacement/dp/B00R1J9DZ6

I tested again just like you said on post #19 but with this L/C

No force on the L/C 57mV
As I applied force the output would go up, up to about 360mV

The behavior from this load cell was perfect! Here is a graph I took:

Now I really think the load cell is broken or something is not right with it.

Do you know how could a load cell break or malfunction? Maybe I applied too much force when testing?

Edit: Should I test (with the old load cell) post #19 by inverting Green and White?

 

hi k,
Pleased to hear you are making progress.
Note that you new L/C has the following specs:

Rated load: 10kg /22lb; rated output: 1+/-0. 15mV/V
Input resistance: 1066 +/- 20 Ohm; output resistance: 1000 +/- 20 Ohm
F. S; recommend excitation Voltage: DC 5V
max excitation Voltage: DC 10V

So I would suggest using a 5Vext voltage, this should give a L/C signal of ~1mV/V, so a change in value of the Rgain resistor will be required.
The increase from 350R to 1000R of the L/C resistance values will not have any effect on the circuit.

Do you know how could a load cell break or malfunction? Maybe I applied too much force when testing?

Many reasons for a L/C failure.
Manufacturing defects.
Excessive force applied to the cell
Excitation over voltage which could cause heating of the sensor elements.

Should I test (with the old load cell) post #19 by inverting Green and White?

You could repeat the tests in order to confirm your original measurements.

E

BTW:
What is the required voltage range for the INA, Vout to the Arduino analog input.?

 

Hey!

What is the required voltage range for the INA, Vout to the Arduino analog input.?

I believe it to be 5V or 4.5V at max.

I repeated the test to no success :/

this should give a L/C signal of ~1mV/V,

I'm still a little lost on what 1mV/V means, does that mean that my Vout will change by about 1mV/5V (if i use 5V for Vext), which is 200uV for every force amount I apply? I'm not sure if i making sense.

I tested the new load cell and it works perfectly, I even changed Rg from 100 0hm to 10 Ohm and got a bigger range in my output, output went from ~0.05V up to ~2.40V

At this point I think is better to buy a new S-Beam L/C

 

hi k,
The 1mV/V, means that with a 5V L/C excitation, the L/C will output 5mV at the rated load of 10kG.
[so that is 0.5mV for every 1kG increase in load, eg: 5kG loading would give 2.5mV] , its a linear change.

With only a 2.5Vext it will be only 2.5mV at 10kG.

I would recommend using 5Vext so that you get 5mV at 10kG load, amplify that by say 500 will give a Vout of +2.5V.

If you require a +5Vout the INA125 cannot swing that high with only 5V supply voltage, it would mean powering the INA and L/C with 10Volts.

The ADC in Arduino can be programmed [ if it is 12 bit ADC] to give 512 counts for a 2.5Vinput.
Or
you can use a 2.5V reference voltage for the ADC and get 1023 counts for 10kG.

By adjusting the INA Vout to 2.44V, this will give 1000 ADC counts, which means 1000 counts = 10kG.

Do you follow that OK.?

E

 

Yes, Thank You so much for the help! Great explanations! You helped clarify the circuit a lot!

 

Hello eric, hope you are doing well!

I wanted to ask you one last question, I couldn't find a way to private message you in AAC so I'm posting my question here.

I got a new load cell and it is working perfectly with the circuitry you suggested!

My question is: if I invert the signal cables, the green and white cables, will that affect the load cell? Or just affect my output? i.e. Instead of positive voltage it will be negative voltage.

Let me know if my question is clear!

Best,
k

 

hi K,
You should be able to PM me.
If you reverse the Gn and Wh wires, the signals will try to drive the INA amp output below zero volts, which it cannot do as you are using a single INA supply voltage.

E
Pleased to here you have it working, nicely done.
E

 

Hey,

I see. I asked because I have a load cell that goes negative when compressed and positive with tension.
I want to reverse this behavior so that it goes positive when compressed and negative when it has tension.
And I am assuming that by changing the Gn and Wh cables I'll be able to achieve this.

thank you so much!