How to connect multiple load cell outputs together?

Thread Starter

Meca10

Joined Jun 15, 2021
27
I´m making a force plate with 4 500 Kg load cells. I put load cell on each plate corner. I made an instrumentation circuit for every load cell with AD620 and LM358. The LM358 was used to fix the instrumental amplifier offset error. Afterward used an ADC (ADS1115) to read weight readings for each load cell and sending all measurements to ESP32 using I2C protocol.
How can I calibrate all load cells without using a summing circuit or Hx7111 module for obtaining total weight voltage?.

Regards.

Meca.
 

ericgibbs

Joined Jan 29, 2010
16,409
hi M,
Usually all 4 L/C's are connected in parallel.
Check this PDF.
E

Clip:
Most industrial load cells are used in multiple load cell weighing systems. Load cells should be
electrically connected in such a way that the signal (output) lines, excitation (power supply) and sense (when present) lines are in parallel. Usually the connection is not made at the indicator, but in a separate housing, a so called junction box, located adjacent to the weighing system.
 

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Thread Starter

Meca10

Joined Jun 15, 2021
27
Hi Eric
I read Pdf sent to me. However, I have doubts. Can you give me other example about the calibration process using excitation trim configuration?.

Please if anyone has experience using parallel Load Cells configuration. Can you give me an explanation how calibrate them?

Thanks
 

Thread Starter

Meca10

Joined Jun 15, 2021
27
Eric I don't use Hx711. I connect 4 load cells on parallel and put signal(+) and signal(-) on Ad620

Could use an instrumentation amplifier?
 

ericgibbs

Joined Jan 29, 2010
16,409
hi,
When I make Load Cell platforms [ for animal weighing] , I use 4 L/C's of the same specification, connected into INA amp.
What are you connecting the INA output into.?

Almost the same as your specification.
E


Update:
Please post a digram of the project.
 

Beau Schwabe

Joined Nov 7, 2019
129
The Hx711 is basically an Instrumentation amplifier connected to a 24 bit ADC. A micro directly reads the ADC and provides the information serially. Conveniently it also includes a voltage regulator. The 24 Bit ADC and micro eliminate a lot of the noise problems that can parasitically enter the system using discrete components.
 

ericgibbs

Joined Jan 29, 2010
16,409
hi M,
Have you built the circuit in your posted images.?
If yes, they should work OK.
The AD620 is an INA Instrumentation Amplifier.

What question are you having a problem with.?

E
 

Thread Starter

Meca10

Joined Jun 15, 2021
27
hi M,
Have you built the circuit in your posted images.?
If yes, they should work OK.
The AD620 is an INA Instrumentation Amplifier.

What question are you having a problem with.?

E
Yes Eric I built the circuit on post images. However I can't calibrate the load cells because on documentation said that I need full load for make measurement LC output. The weighing machine has 2 Ton max capacity weight and I don't have 500 kg for calibrate each LC.
How calibrate system without all load?
 

ericgibbs

Joined Jan 29, 2010
16,409
hi,
Is the scale being used weigh commercial resale products, if Yes you should hire a company that can calibrate the weight platform and issue you with Calibration Certificate/s

What are you weighing on the scale.?

E
 

Thread Starter

Meca10

Joined Jun 15, 2021
27
hi,
Is the scale being used weigh commercial resale products, if Yes you should hire a company that can calibrate the weight platform and issue you with Calibration Certificate/s

What are you weighing on the scale.?

E
Eric I make a force platform. It's some similar to weighing machine. The FP is used to measure athlete ground reaction forces (GRF)
 

Thread Starter

Meca10

Joined Jun 15, 2021
27
Hello

I have a doubt about how to calibrate load cell array. I used excitation trim schema for connect in parallel four load cell. I send Sig(-) and Sig(+) pins to Hx711 module. However I don't know exactly How to calibrate load cells using excitation trim circuit. Someone can explain me?. The Trimmer value for each load cell is the 100 Ohms.

Thanks.
 

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Last edited:

Thread Starter

Meca10

Joined Jun 15, 2021
27
hi Meca,
Look at page #2 of this PDF.
E
Hi E
I am reading page #2 and this recommend used high sensitive voltimeter a least 42 digits for pre trimming the potentiometers. I don't have multimeter with high sensitivity. Do you have any alternative for make calibration process with commercial multimeter?
 
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