Load cells are sensors that output extremely low levels of voltage. When converted to a weighing indicator value, the gradations are often 0.5 μV or less. (This tiny voltage is equivalent to about 1/3,000,000th of that of a battery.) Furthermore, output voltage of the load cell is proportional to excitation voltage. While load cell wiring and connections may appear unusually difficult at first glance, errors can be greatly reduced by observing a few important points. Point 1: Use six-wire cable As was stated above, it is best to use six-wire cable, as the remote sensing function corrects errors due to conductor resistance and other causes. Point 2: Use the shield wire and ground properly(Ground on the weighing indicator side) A shield wire protects the minute output signal of the load cell from surrounding electrical noise. Point 3: Use well-insulated cables and terminals Well-insulated cables and terminals prevent negative effects on the minute output signal. Insulated cables and terminals allow you to maximize the potential of the load cell. We recommend proper load cell wiring for accurate measurement.

The above shows the wiring relations of the cable attached to the load cell and the six-wire shielded load cell cable. Junction boxes and summing boxes are used to actually connect them. A&D’s junction boxes, summing boxes, and weighing indicators with terminal connections have well-insulated terminals. The optional six-wire shielded cable is also well insulated.

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.

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

The common procedure is as follows:

Below is an example of how to connect an indicator and a load cell.

Suppose we prepared a load cell whose capacity is larger than 3.6kg to measure 3kg. We would like to display the results using an indicator, but what kind of indicator should we use? The specifications of the load cell and the indicator are as follows:

Let’s presume that the load cell will output approx. 12mV when 3kg is loaded,

Suppose the indicator displays the weight in units of 0.1g between 0 and 3kg. This 0.1g is called the minimum scale division. As 3kg is divided by 30000 divisions (0.1g), the resolution is said to be 1/30000. Per 0.1g, the output will be:

The input sensitivity of the indicator is 0.33μV.As this value is smaller than 0.4μV, we can use this indicator. If the input sensitivity is larger than 0.4μV, the indicator cannot display the weight in units of 0.1g.

A load cell is a transducer that receives force in the form of a load and converts it into electronic signals. Devices such as indicators, computers or other measuring devices are necessary to display and use the electrical signals. The outputted values can then be saved in a database or printed and organized in various ways.

The following is an explanation of how to connect a load cell to an indicator:

The output cables of a load cell consist of two power cables (+/-), two signal cables (+/-), and one sield cable. There are five cables in total.

To reduce the risk of error, seven cables are sometimes used, with two additional sensing cables.

The instruction manuals of both load cells and indicators describe the kind and the color of each cable, so you can simply match and connect two cables of the same kind and color.

Once the cables are connected, it is necessary to conduct the calibration and set the various option settings. The required settings differ with different products, so it is highly recommended that you read the instruction manual.

Load cells are generally made from metals such as aluminum, iron and stainless-steel.

Listed among the load cell specifications, you can find the “fatigue life” of the load cell. The fatigue life indicates the number of times a rated capacity can be loaded.

For instance, if the fatigue life is 100,000 times, the weighted capacity can be loaded 100,000 times. When loading occurs more than 100,000 times, the load cell may not perform as well as guaranteed by its specifications.

Sudden shock or applying force that exceeds the rated capacity for a long time will damage the load cell. However, with proper usage, maintenance, and protection, the load cell can be used for many years, if not decades

The measurement principle for load cells is as follows:

Load Cells are classified into the following shapes:

It is important to use the load cell with the capacity and structure appropriate to the position where it will be used.

Example 1)
Single point load cells are often used for ordinary (small to medium sized) scales. The load point of the single point load cell is placed under the center of the weighing pan.

Example 2)
For industrial scales such as tanks and hoppers, beam and column load cells are normally used. One or multiple load cells may be necessary, but when using multiple load cells, the load applied onto each load cell should be even.

Example 3)
“S” load cells are typically used for tension measurements.

In various industries, it is becoming increasingly necessary to measure and computerize the weight (mass) of products in order to improve quality and productivity, and to reduce costs. The computerized data is often used for inspections and aggregate calculations.

Inside instruments (systems) that measure mass, load cells function as sensors that convert physical force into electrical signals. These electronic signals are then manipulated and finally the results are displayed on monitors for computers or other devices, or printed and saved.

Load cells are used for quick and precise measurements. Compared with other sensors, load cells are relatively more affordable and have a longer life span.