Views: 136 Author: Site Editor Publish Time: 2021-05-17 Origin: Site
Does load cell excitation voltage matter?
As stated previously, load cells require an excitation voltage to produce an output signal. A higher excitation voltage will produce a higher output voltage swing when a load is applied to the cell. So, bigger is better, right?
Yes, to a degree. Larger signals are easier to measure and digitize. Additionally, assuming the noise is constant, the ratio of signal to noise (SNR) increases. This is good from a data quality standpoint.
However, a high excitation voltage has drawbacks. Higher voltages through the resistive strain gauges (which comprise the Wheatstone bridge) will cause more current to flow and heat the strain gauges. The cell body acts as a heat sink to keep the gauges cool. If the maximum rated excitation voltage is exceeded, the heating will cause signal perturbation or gauge failure. Additionally, in battery operated devices, high excitation voltage (and thus, current) will cause the battery to deplete much faster than with lower excitation voltages through the circuit.
Excitation voltages lower than the manufacturer’s stated maximum are acceptable for the given load cell. The manufacturer’s recommended value is obviously best, but there is no harm in a lower excitation voltage. For example, 5V is a very common excitation voltage for modern load cells. Modern instrumentation amplifiers are much better than old designs and their output signals are not compromised by the lower excitation voltage. It is perfectly fine to use a 5V excitation amplifier with a 10V recommended excitation load cell. (However, the converse is not true!)
Finally, when choosing the excitation voltage, consider the common mode voltage produced by the cell’s output. The amplifier or other signal conditioning electronics must be able to handle this common mode voltage, whose value is 50% of the excitation voltage. For example, a 10V excitation produces a 5V common mode voltage. Typically these amplifiers provide the excitation voltage to the cell; when this is the case, an external excitation voltage is not recommended.