Issue with UTILCELL Model 620 Load Cell and MCC USB-2404-ui Data Acquisition: Extremely Low Voltage Values

[Otman]

Hello everyone,

I am working on a project involving the UTILCELL Model 620 load cell with a nominal load of 500 kg and the MCC USB-2404-ui data acquisition device. However, I have encountered an issue that has puzzled me, and I need your assistance to resolve it.

While testing with Instacal and working with DASYlab, I noticed that the voltage values I obtained from the load cell were surprisingly low, reaching the range of 1e-5 V/V. Although I am confident that the data acquisition device is reading the load cell, as the values vary when a load is applied, I am concerned about the accuracy of the results.

I have attached an image displaying the connection I have set up for your reference.

After analyzing the situation, I suspect that the problem may be related to calibrating or scaling the values obtained from the load cell. However, I have no prior experience in dealing with such issues, and I am unsure of the proper steps to address them.

Therefore, I kindly request your knowledge and expertise in this area. Has anyone encountered a similar issue or do you have any ideas on how I can tackle this problem? I would greatly appreciate your suggestions or steps I can follow to calibrate the load cell properly and obtain accurate voltage values.

Thank you very much for your time and assistance! I am eager to hear your feedback and resolve this inconvenience to proceed with my project smoothly.

[JRys]

The USB-2404-UI returns millivolts per volt of excitation power - mV/V sensitivity. It uses the excitation power as a reference to the A/D. If the excitation power fluctuates, it will not change the accuracy of the measurement. Some devices use a fixed excitation power and return millivolts. If the excitation power fluctuates, the accuracy will suffer. So what they do is use another pair of wires as feedback to regulate the power. Long story short, when loaded to 500kg, your load cell should return 0.002 volts. You should have received a calibration sheet with the load cell with the calibrated sensitivity rating. For instance, instead of the nominal 2mV/V, is may be 2.1mV/V at 500kg. Make sense?  

[Otman]

4 hours ago, JRys said:

The USB-2404-UI returns millivolts per volt of excitation power - mV/V sensitivity. It uses the excitation power as a reference to the A/D. If the excitation power fluctuates, it will not change the accuracy of the measurement. Some devices use a fixed excitation power and return millivolts. If the excitation power fluctuates, the accuracy will suffer. So what they do is use another pair of wires as feedback to regulate the power. Long story short, when loaded to 500kg, your load cell should return 0.002 volts. You should have received a calibration sheet with the load cell with the calibrated sensitivity rating. For instance, instead of the nominal 2mV/V, is may be 2.1mV/V at 500kg. Make sense?  

How should I connect the 6 wires of my load cell to the DAQ device considering that two of these wires are for regulating power?

Additionally, if I want the USB-2404-UI to provide measurements in kg, should I follow these calculations?

- Nominal load (Sn): 500 kg
- Calibrated sensitivity (Sc): 1.9994 mV/V
- Voltage (V): 10 V
- Maximum Voltage (Vm) = Sc * V = 1.9994 * 10 = 19.994 mV
- Scaling Factor (Sf) = Sn / Vm = 500 / 19.994e-3 = 25007.50 kg/V

Finally, do I need to input the obtained scaling factor into DASYlab, as shown in the attached picture?

[JRys]

To understand the other two wires, you must realize a four-wire measurement. Excitation current runs through the Excitation wires and will drop voltage if the cables are long. The other two wires (Sense wires) carry no current and measure the voltage at the sensor. So a four-wire measurement can accurately measure the voltage of the device when long cables are used. The USB-2404-UI cannot accommodate long wire runs. So, you can either leave them unconnected or shove them into the same terminals as the excitation wires. 

As for scaling to engineering units, you're on the right path. However, I prefer to use the Enter 2 points because it's easier. X1=0.000, X2=0.0019994, Y1=0, Y2=500000, and DASYLab will figure it out.

[Otman]

On 7/18/2023 at 7:52 PM, JRys said:

To understand the other two wires, you must realize a four-wire measurement. Excitation current runs through the Excitation wires and will drop voltage if the cables are long. The other two wires (Sense wires) carry no current and measure the voltage at the sensor. So a four-wire measurement can accurately measure the voltage of the device when long cables are used. The USB-2404-UI cannot accommodate long wire runs. So, you can either leave them unconnected or shove them into the same terminals as the excitation wires. 

As for scaling to engineering units, you're on the right path. However, I prefer to use the Enter 2 points because it's easier. X1=0.000, X2=0.0019994, Y1=0, Y2=500000, and DASYLab will figure it out.

Thank you very much! Your help has been so helpful! :D