- March 18, 2019
Troubleshooting Method For Load Cells
Understanding how load cells work can seem complex for some people. In most of the cases, a simple fault-finding guide is all you need to help you understand load cells and their operating mechanisms. We will be going through some of the examples below.
Load cells produce a very tiny output, commonly in the range of mV/V. Therefore, load cells require a signal amplifier to amplify the signals to be readable in the measurement instrument. A tiny error in measurement signal can show up in the instrument which can come from many sources.
Commonly, the solution lies in using screened, twisted pair cable along with a good quality signal conditioner to eliminate the noise. However, sources of the error may come from either the load cell itself, the cable or the signal amplifier.
Fault Finding in Load Cells
- Check the wiring connections between the signal conditioner and the load cell. Ensure that the wires are connected per the colour coding prescribed by the manufacturer. Use the load cell’s calibration certificate to check for manufacturer’s instructions.
- On the calibration certificate, you will also find the resistances between signal +/- and excitation +/-. Measure these resistances using a multimeter to ensure that the sensor does not suffer any internal damage.
- Take a look at the load cell. Does it move freely? If there are mechanical restrictions, the load cell’s output will be affected. Poor cable routing can be a cause for skewed readings. Ensure that the cable routing is free to move.
- Check for overload in load cell. Overloading can permanently deform the load cell and keep it from returning to its zero position correctly.
Fault Finding in Cabling
- Ensure that the signal conditioner and load cell are not too far apart. The greater the distance, the higher the chance of the cabling falling prey to capacitive coupling and electromagnetic fields.
- Check to ensure that the sensor cables are not running anywhere near the inductive loads.
- Use twisted pair, screened cable as it helps to reduce the magnetic influence of power cables. Also, check to ensure that the cable is screened and connected to ground only at one point.
- Test cable continuity for the integrity of the cabling.
Fault Finding in Signal Conditioning
- Check the excitation voltage of the signal conditioner.
- Check how many load cells have been connected. If there are too many, it may not work. You can check the cell’s total resistance using a multimeter. Before doing so, however, you must also check the specification on the signal conditioner for the minimum load.
- Shorting between the inputs on the signal conditioner. This should simulate a zero load resulting in a zero output.
- If the signal conditioner you are using has a shunt cal function, ensure that it is not active as it may interfere with correct readings.
- If you are pairing a four-wire load cell with a six-wire conditioner, link the excitation and sense terminals appropriately. If they are not correctly linked, you will not see a sense input, which means no reference point.
- Check whether the output from the signal conditioner matches with the input needs of the display.
- Check to ensure that the positive direction corresponds with the required positive reading.
- Check to ensure that gain and offset are correctly set. You may need to recalibrate using the reference manual at this point.
At Measurex, we supply world-class sensor technology including load cells, signal conditioners, pressure sensor, displacement sensor, rotary sensor and strain sensor. Get in touch with us today to discuss your application.