A load cell is a force transducer. It converts an applied force into an electrical signal that can be measured. The electrical signal changes proportionally to the force applied. Multiple kinds of load cells exist: hydraulic, pneumatic, etc. but we are focusing on the most common type – strain gauge load cells.
The MonoDAQ-U-X is capable of both powering the load cell and logging data directly from the cell without the need for any additional external components. Up to four 4-wire load cells or up to two 6-wire load cells can be connected to a single MonoDAQ-U-X device.
Connecting the load cell
Load cells usually consist of a metal body to which strain gauges have been fitted in a Wheatstone bridge configuration. The cell is powered by an excitation voltage and the force can be derived from the voltage difference on the signal wires. Strain gauge load cells are a widespread, accurate, and cost-effective solution for measuring force.
On the left is a diagram of a load cell and on the right the Wheatstone bridge on which it is based.
The wire color code we used (red and black for excitation and green and white for signal) is commonly encountered but by no means is it the only one. Make sure to consult the loadcells datasheet to determine what color code your cell uses
Single load cell
Since the MonoDAQ-U-X comes with native support for strain gauge load cells all we need to do is select the strain gauge option from the channel 1 function drop-down menu.
Excitation is automatically set to 5V which is the standard for most strain gauge load cells.
Multiple load cells
Up to four load cells can be connected this way.
It should be noted that all four load cells share the same excitation. This could lead to a voltage drop in the excitation wires (red and black). If force is being calculated from a mV/V to force conversion from the load cell’s datasheet this could lead to measurement errors. In this case, the excitation wires should be kept short or thick enough to minimize the voltage drop.
Alternatively, the load cells can be calibrated manually which circumvents this problem.