# How can I improve the accuracy of my load cell signal output?

• elixirnova
In summary, the conversation discusses the use of a load cell, which is a wheatstone bridge strain gauge, and the need to provide it with 9Vdc or 12Vdc excitation voltage. The output from the load cell is recorded using a NI USB 6009 DAQ. The goal is to maximize the sampling rate and improve the output accuracy, which requires "zeroing" the output voltage and scaling it up to +/- 10V. The suggested solution is to use a low noise op-amp or an instrumentation amplifier. Additional information on the load cell's input and output resistance is also provided.
elixirnova
Howdy,

I am a mechanical engineering student with limited circuitry knowledge to start...

Anyhow I have a [-500,+500]lbf load cell that is essentially a wheatstone bridge strain gauge. I want to give it either 9Vdc or 12Vdc excitation voltage since I have a regulated power supply that can output those voltages. The load cell is rated for 10V excitation with a maximum of 15V though.

Anyhow here is my problem. I am using a NI USB 6009 DAQ to record the voltage output from the load cell. At zero load I tested the voltage outputs for both 9V and 12V input excitation voltages.
9V input -> 4.19V output
12V input -> 5.65V output

The Full Scale range of operation I hope to use this load cell in would result in a maximum/minimum increase in output voltage to
9V input -> 4.19V +/- 0.027V output
12V input -> 5.65V +/- 0.036V output

The other device I have is the USB 6009 DAQ that can ready +/- 10Vdc but it has limited resolution, if I hook the system up to the DAQ without conditioning the output signal I only get +/-5lbf output accuracy and that is when sampling at 1hz. I would like to maximize how fast I can sample and greatly improve the output accuracy. So I figure I need to "zero" the output voltage with a circuit and I suppose scale the output up to +/- 10V.

I hope I am not asking too complex of a question. I just don't really know where to begin. All I have come up with so far is:
-Low Noise Op-Amp to apply a GAIN to the output signal and power it with the DC voltage source
-Use a voltage divider circuit in parallel with the excitation source voltage to "zero" the output voltage.

I must not be doing any of it right though since the circuits I have thrown together from guides on the net have not done anything that I am wanting them to do :(.

Any help on where I need to look now?

Here is some other info on the load cell
Nominal Input Resistance: 394ohms
Nominal Output Resistance: 350ohms

Would an instrument amplifier with a setup such as the one posted in another PF topic work?

I suppose it is called a voltage difference amplifier. I suppose I could have one input voltage be my load cell output and have a 2nd power source of 5V which would give me an output of Vo = 0.65*A where A = R3/R1 and I could amplify the signal with a gain of about 14.5 which would give me Vo=9.425V nominal and Vo=9.86V FS (500lbf load).

Although I hear that I shouldn't be using an op-amp for a load cell amplifier. Instead I should be using an instrumentation amplifier. Can I perform a voltage difference amplifier with an Instrumentation amplifier as well??

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You could use op-amps or instrument amps. Depends on your cell and what you want to do. e.g. how many varying elements, temperature compensation, linearizing.
I found this http://www.analog.com/static/imported-files/seminars_webcasts/49470200sscsect2.pdf" that might help in you circuit design.

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## 1. What is a load cell signal output?

A load cell signal output is a type of electronic signal that is generated by a load cell, which is a device used to measure force or weight. This signal is typically in the form of a voltage or current and is used to indicate the amount of force or weight being applied to the load cell.

## 2. How is the load cell signal output measured?

The load cell signal output is measured using a device called a load cell amplifier, which is connected to the load cell. The amplifier converts the signal into a usable form, such as a digital readout or a value that can be recorded by a computer.

## 3. What factors can affect the accuracy of the load cell signal output?

Several factors can affect the accuracy of the load cell signal output, including temperature changes, electrical interference, and overloading of the load cell. It is important to regularly calibrate the load cell and ensure it is not exposed to extreme conditions to maintain accuracy.

Yes, the load cell signal output can be adjusted by using a calibration process. This involves applying known weights or forces to the load cell and adjusting the output signal until it matches the expected values. Proper calibration is important for accurate and reliable measurements.

## 5. What are some common applications of load cell signal output?

Load cell signal output is commonly used in industrial and scientific applications for measuring weight or force. It is often used in scales, tension and compression testing machines, and material testing equipment. Load cell signal output is also used in robotics and automation to control and monitor the amount of force being applied by a robotic arm or tool.

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