How to calculate the signal that a load cell delivers by division (?V/div)?

The signal that one or several cells of a weighing system deliver for a specific increase of load, normally the display division, is:

?u = (C * 1000 * Uexc * e) / (N * Emax )

Where,

?u = Increase of signal in ?V/div (micro?volts/division)
C = Nominal Sensitivity of the cell in mV/V
Uexc = Excitation Voltage of the cells in V (Volts)
e = Size of the division in kg
N = Number of load cells
Emax = Nominal capacity of the cells

Typical values:

?u = 0,8 a 5 ?V/div (micro?volts/division)
C = 1 a 3 mV/V (milli?volts per volt)
Uexc = 3 a 12 V (Volts)
e = 0,001 kg a 100 kg
N = 1 a 10
Emax = 1 kg a 400.000 kg

Examples:

Ej. 1) Scale of Max range=15 kg, division e=0,005 kg (5g)
N = 1 cell of Emax = 20 kg, C= 2mV/V
Load Cell Excitation Uexc = 10 Volts

?u = (2 * 1000 * 10 * 0,005) / (1 * 20) = 5 ?V/div

Ej. 2) Same example as Ex.. 1) but with Load Cell Excitation at Uexc = 5 Volts

?u = (2 * 1000 * 5 * 0,005) / (1 * 20) = 2,5 ?V/div

Ej. 3) Scale of Max range= 600 kg, division e=0,200 kg
N = 4 cells of Emax = 500 kg, C= 2mV/V
Load Cell Excitation Uexc = 5 Volts

?u = (2 * 1000 * 5 * 0,2) / (4 * 500) = 1 ?V/div

Ej. 4) Scale of Max range= 1500 kg, division e=0,5 kg
N = 4 cells of Emax = 750 kg, C= 2mV/V
Load Cell Excitation Uexc = 6 Volts

?u = (2 * 1000 * 6 * 0,5) / (4 * 750) = 2 ?V/div

Ej. 5) Same scale as Ex..4) with slightly bigger cells:
N = 4 cells of Emax= 1000 kg, C= 2mV/V
Load Cell Excitation Uexc = 6 Volts

?u = (2 * 1000 * 6 * 0,5) / (4 * 1000) = 1,5 ?V/div

Ej. 6)
Truck weighing type scale of a Max Range of =60.000 kg, division e=20 kg
N = 6 cells of Emax = 20.000 kg, C= 2mV/V
Load Cell Excitation Uexc = 10 Volts

?u = (2 * 1000 * 10 * 20) / (6 * 20.000) = 3,3 ?V/div

Ej. 7) Truck weighing type scale of a maximum Range =60.000 kg, division e=20 kg
N = 8 cells of Emax = 30.000 kg, C= 2mV/V
Load Cell Excitation Uexc = 6 Volts

?u = (2 * 1000 * 6 * 20) / (8 * 30.000) = 1 ?V/div

Recommendation:

As we have seen in the examples above, the signal values that the cells deliver per each “display” division are very small; between 1 and 2 ?V/div. Therefore, specific high sensitivity electronic instruments should be used for the load cells, that have super?stable power supply voltages, stable differential amplifiers, high resolution analog?digital converters of between 16 and 24 bits and filters and suitable protections.

The shielding of the conduit of the cell wires and a grounding of the complete system will help to protect these weak signals in environments with interferences, such as the industrial ones.