Expertise & Technical documentation
Selection of Weighing Instrument For Load Cell
Selection of weighing instrument for load cell
This paper briefly introduces how to select the weighing instrument according to the voltage signal of the weighing sensor for reference.
In a standard weighing instrument, the matching of weighing instruments has been selected by engineering designers. However, if a weighing instrument with special structure or the old weighing instrument is reformed, the selection of load cell and supporting instrument is a problem that must be considered.
(1) Excitation voltage from the instrument to the load cell:
Each special weighing instrument is usually equipped with a set of regulated DC power supply, which is sent to the sensor as an excitation voltage (bridge output voltage)
For general weighing instruments, the voltage is 5V, 6V, 10V, 12.5V and 15V. It must adapt to the recommended excitation voltage of the selected sensor. The load cell is allowed to be used under voltage, but it is better not to exceed the recommended voltage.
(2) Load capacity of instrument:
The output power of the excitation voltage source supplied by the weighing instrument to the weighing sensor is limited. Therefore, the number of sensors it can accept is limited. This will be given in the operation manual of the instrument.
(3) The length of the connecting cable from the instrument to the sensor is easy to understand, and the length of the cable from the sensor to the weighing instrument should be limited because of this cable
There is a considerable current on the core wire that outputs the excitation voltage to the sensor. Due to the action of wire resistance, it will cause the excitation voltage sent to the sensor to be lost (reduced), thus affecting the work of the load cell. The length of this cable will be given in the operation manual of the weighing instrument, so it should be consulted if necessary. In addition, if a slightly longer transmission distance is required, the method of thickening the cable core can also be used.
(4) "Microvolt / division value" of weighing instrument（ μ Verification of V / D) value: amplifier is built in any weighing instrument. All amplifiers must have a linear amplification area, that is, if the input signal is too small or too large, the output of the amplifier will be abnormal. Taking Toledo 8142pro instrument as an example, its input signal range is 3MV ~ 30mV; The display output value of the digital weighing instrument always increases or decreases by an integer multiple of the set division value. Therefore, the microvolt number of the input signal corresponding to the output of each division value can be used as a characteristic value of the weighing instrument, that is, the so-called "microvolt / division value"（ μ V / D) value can be used as a characterization value. The manual of each weighing instrument is usually attached with a table indicating the "microvolt / division value" of the instrument（ μ Allowable range of V / D). Whenever we select the model, number of sensors and instruments used, we should check whether this configuration meets the provisions of "microvolt / division value" of the instrument. Sensitivity of selected sensor: 2mV / V; It is estimated that the output excitation voltage of the selected instrument is 15V. According to the above parameters, we can get the total output of the sensor: 2mV / v × "Microvolt / division value" value of 15V = 30mV instrument: division number of the instrument n: 5000kg / 1kg = 5000. Check the value given in the instrument instructions. It is found that 8142 instrument (single display) requires "microvolt / division value" of 0.6 when it is used at 5000 division μ v/d~7.0 μ V / D, so the above configuration is available.
Note that in the multi-sensor weighing system, (4 or more), if the value of "microvolt / division value" is less than 0.3 μ V / D, or in a single sensor weighing system, the "microvolt / division value" value is less than 1 μ At v / D, the working state of the scale will be very unstable; If the value of "microvolt / division value" is greater than the maximum allowable upper limit, the weighing instrument will not enter the verification state.
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