Problems in Manufacture and Application of Six Wire Load Cell

Problems in Manufacture and Application of Six Wire Load Cell

[Abstract] Six wire weighing load cell is a kind of weighing load cell with long-term compensation function. It can effectively reduce the influence of wire on load cell output and realize long-distance test. However, unreasonable use method will cause great measurement error when using electronic weighing instrument. This article analyzes the relevant problems to attract the attention of relevant manufacturers and users.

[Key words] Weighing Load Cell, Six wire load cell, The load cell is affected by temperature, Weighing Indicator

The load cell can adopt two different input and output wiring methods, one is four wire connection method, the other is six wire connection method (see Figure 1); the four wire connection method has no special requirements for the secondary instrument, so it is convenient to use, but when the cable line is relatively small, it is easy to use For a long time, it is easy to be affected by environmental temperature fluctuation and other factors, thus affecting the measurement performance of electronic weighing indicator; the weighing load cell with six wire connection method requires that the secondary instrument used with it should have feedback input interface, so the application range has certain limitations, but it is not easy Due to the influence of environmental temperature fluctuation and other factors, it has certain advantages in precision measurement and long-distance measurement.

Four wire Connection                      Six wire Connection

At present, many load cell manufacturers in China produce two different types of load cells at the same time, but we found an amazing fact in our contacts with many sensor manufacturers in our province. Some enterprises have not made any changes to the manufacturing compensation process, but simply use four or six core wires to produce four wire or six wire weighing sensors, and neither have we In the user's manual, the user's Manual shall explain the possible measurement error caused by the limitation or wrong use of the six wire load cell;

It is suggested that load cell manufacturers and users should pay close attention to the following two issues:

1. The problems that must be paid attention to in the manufacturing process of the six wire weighing load cell, as an important part of the sensor, the cable has an important impact on the measurement performance of the load cell; because the core wire of the cable is made of copper wire, and the resistance temperature coefficient of copper is about 0.004/℃ In other words, the cable not only affects the load cell's output sensitivity coefficient because of its own resistance, but also affects the load cell's coefficient temperature due to the change of the cable's resistance with the temperature. Therefore, the cable must be put into the compensation box for the temperature compensation of the sensitivity coefficient of the load cell. However, for the six wire connection method of the load cell, due to the existence of the feedback line, the cable does not affect the output sensitivity coefficient of the sensor. Therefore, if the ordinary non six wire measuring instrument is used for temperature compensation of the sensitivity coefficient of the load cell, the cable can not be put into the compensation box together, otherwise the sensor will produce serious under compensation, unless the six wire system is used for compensation For example, if the input impedance is 380 Ω and the cable length is 10 meters (if the line resistance is 2×1.5= 3Ω), the under compensation is about 0.015% /10℃, which is far beyond the standard requirements of C3 level load cell. Due to the vast territory of our country, the temperature difference between winter and summer in most areas is about 40℃, so the environmental temperature difference will bring about 0.06% weighing error to electronic weighing instrument. Therefore, load cell manufacturers must develop different production processes according to different types of load cell.

2. The problems that must be paid attention to in the use of the six wire weighing load cell have been mentioned earlier. The influence of the cable on the sensitivity coefficient is not considered in the compensation process of the six wire weighing load cell, so the measuring indicator suitable for the six wire weighing load cell must be selected; in fact, for the electronic weighing instrument that uses more than one weighing sensor, the measuring instrument must be selected, It is usually connected to the weighing instrument after parallel adjustment through the junction box; as far as we know, when some weighing instrument manufacturers use the weighing sensor, the excitation and feedback of the six wire sensor are simply connected in parallel with the four wire system into the junction box, and then the six wire cable is pressed into the six wire cable Connect to the instrument by wire system; or cut part of the cable of the four wire sensor and connect it to the junction box, and then connect to the instrument according to the six wire system. In fact, the two connection methods destroy the original temperature compensation effect of the weighing sensor, which makes the electronic weighing instrument produce great weighing error due to the temperature difference between winter and summer. The accurate use method is that when using the six wire weighing sensor, the feedback line of the weighing sensor should be directly connected to the feedback line port of the weighing instrument, and it is not allowed to short circuit the same polarity excitation with the feedback line in the junction box It is not allowed to change the original length of the sensor cable before it is connected to the junction box, while the six wire connection method must be used between the junction box and the instrument. 3. Problems that must be paid attention to in the test process of six wire weighing sensor. Because the appearance of six wire sensor and six wire four wire sensor can not be distinguished, therefore, before testing the sensor, if the sensor input and output cable has six wires, it should be clear whether the sensor is a six wire sensor The test of six wire weighing sensor can not be carried out by precision digital voltmeter, but active measuring instrument with feedback interface must be used. The commonly used test instruments include dmp39, dk38, mgcplus and other German made precision digital measuring instruments and some domestic special sensor 2 Weighing Technology 2008 Qingdao test instrument. During the test, it must be ensured that each wire of the weighing sensor is directly connected to the corresponding ports of the measuring instrument, otherwise, the measurement error will be larger.