How to Choose Digital Weighing Display

Digital weighing display is an instrument that provides DC excitation voltage for weighing sensor, amplifies millivolt signal and converts it into digital output. In addition, in order to meet the needs of modern technology, digital weighing display can also have many other functions
Most digital weighing displays are designed to provide 10-15v DC voltage to excite up to eight 350 Ω load cells. However, some displays are limited to a maximum of four 350 Ω load cells. This paper will discuss what kind of display should be selected when the truck scale with six load cells and the tank truck scale or bucket scale with four sensors must be used.
Usually, when users get used to a type of display, they want all scales to use it. Other types of displays are often ignored unless a standard display cannot meet certain requirements in operation.
The following technical parameters must be considered when selecting the best or most suitable display.
1. Accuracy
Some manufacturers have specified that their display nonlinearity is ± 0.01%. Others do not mention accuracy at all. Generally, the internal division range of the display ranges from 50000 to 130000. Generally, the external display division is limited to 10000. This is the result of the new ntep regulation. Except for some automatic control processes, most displays do not need more than 10000 divisions (see Figure 2). In order to meet the needs of automatic control process, a display with up to 50.000 divisions has been developed.
2. Calibration procedure
Some displays first use the internal dip change-over switch for coarse adjustment of zero point and full scale, and then use the keys on the front panel for fine adjustment. The traditional calibration method of the old model display is to use dip switch for coarse adjustment, and then potentiometer for fine adjustment. The latest type of display does not need to be calibrated with dip change-over switch and potentiometer, just use the keys on the front panel of the instrument for full digital calibration.
Usually, there is an interaction between zero setting and range adjustment. This will cause the scale calibrator to load and unload many times before the system is finally calibrated. For tank truck scale and funnel scale, this is very troublesome and high cost. Therefore, it is recommended to select a display that does not affect each other between zero point and range.
3. Temperature coefficient
When the display is indoors and the temperature changes little, this factor can often be ignored. However, when the display is outdoors or the temperature fluctuates greatly, this factor must be seriously considered.
Generally, the coefficient specified by the existing digital display is 5 ~ 7ppm / ℃. However, some displays are not specified, while others are ± 0.002% F.S. / ° F, that is, 36ppm / ℃. Therefore, if this display is used outdoors, such as the truck scale in the scale shed with heating equipment, the temperature may vary from - 40 ° f in winter to + 70 ° f in summer, and there may be 132 pounds of display deviation for 60000 pounds of load. Under the same conditions, the deviation of other displays is only 18.3 pounds.
4. Interface
When the display and some other devices This performance should be considered when connecting (such as printer, remote display, computer, tape recorder, etc.). Some displays have a standard serial interface with RS232C or 20mA current ring, while others do not have a standard interface, but have a field installation position suitable for serial or BCD interface. Due to the small printed circuit board, this installation becomes easy. Its advantages The point is that the cost of basic units is very low. There is a display with standard RS232C interface and six other selection functions including extended serial line. This adds another bidirectional RS232C port and a 20mA current loop serial output. With the bidirectional RS232C port connected to the computer, a series of commands can simulate the keys on the front panel, transmit the weight value and change the set point remotely. 20mA current loop can be set actively or passively to provide long-distance communication. In addition, with other functions in the display, there can be 4-20mA analog output, BCD output and up to 8 set points.
5. Number of data updates per second

Some displays update data four times per second, which can give a stable reading to a typical platform scale, but it is not suitable for automatic process. Other displays that update data 20 times per second can be well used for process control. One type of display uses laps to select three or ten updates per second. The manufacturer believes that ten times shall be selected for less than 3000 display divisions, while three times shall be selected for 3000 to 10000 display divisions.

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