Determining the maximum cable length when using the remote sensor function with A&D’s weighing indicators

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To determine the maximum cable length, the following values are necessary: the cross-sectional area of cable conductor, the electrical resistance between input terminals of the load cell, and the number of load cells. When using A&D’s weighing indicators, the allowable two-way resistance for cables is about 10% of the resistance between the input terminals of the load cell. Therefore, the one-way resistance is about 5%. The resistance of copper wires with a cross sectional area of 1 mm2 is calculated as 0.02 Ω/m. The formula when using one load cell is as follows: The maximum cable length = the allowable cable resistance ÷ the cable resistance per meter. When two or more load cells are used, the formula is as follows: The maximum cable length = the allowable cable resistance ÷ the cable resistance per meter ÷ the number of load cells.

As an example, let’s calculate the maximum cable length when using three A&D LCC11 load cells with KO162 load cell cables.
The resistance between the input terminals of the LCC11 is 800 Ω.
The allowable cable resistance is 5%. KO162 load cell cables have a cross-sectional area of 0.5 mm2 so the resistance is 0.04 Ω/m.
The maximum cable length = 800 x 0.05 ÷ 0.04 ÷ 3
In this case, the maximum cable length is 333 m.
While the calculated length is 333 m, it may not be possible to use a 333 m cable in some environments (such as areas with a large amount of noise).

The following charts show the relation between the thickness and allowable length of load cell cables.

Are Your Cables Too Thick?

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How do people choose load cells cables? If you look around at customers’ factories, you frequently find cables that are thicker than necessary, probably because they are worried about the resistance of the load cell cable causing measurement errors. In the 1970s, it was common practice to choose a cable that was thick as possible to reduce the negative effects of conductor resistance and temperature changes. All of our current weighing indicators have a remote sensing function that eliminates the need for thick cables. Remote sensing monitors changes in the excitation voltage* of the load cell. During A/D conversion, these changes are corrected to offset errors. The cables have six wires, two of which monitor the excitation voltage. Thinning load cell cables cuts costs and we recommend using cables with the optimal thickness to reduce installation costs.

*Excitation voltage: The application of voltage to an electric circuit from another circuit. Here, it indicates the supply of electrical power to the load cell from the weight indicator.

*How to choose the maximum cable length when using remote sensing with A&D’s weighing indicators