JPS5847008B2 - Weighing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a weighing method in an electronic weighing machine.

Generally, an electronic weighing machine using a resistance wire bridge type load cell as a load detector has a configuration as shown in FIG.

That is, the load cell 1 is excited by a DC power source 2, and the measured output voltage for the applied load W is applied to the amplifier 4 through the bridge balance potentiometer 3.

The measured voltage amplified by the amplifier 4 is adjusted by a span adjustment potentiometer 5, converted into a digital signal by an A/D converter 6, and displayed on a display 7.

Here, the bridge balance potentiometer 3 is connected to the load cell 1 through a connection as shown in FIG. 2, and serves to subtract tare or waste self-defense type as shown in FIG.

In FIG. 3, the A curve gives the load characteristic of the load cell 1, and by operating the bridge balance potentiometer 3 to subtract the tare or unnecessary self-defense load from it,
The A curve is translated in parallel to the 8th curve as shown by the arrow, and as a result, only the measured voltage for the paid load is given as input to the amplifier 4.

On the other hand, the output of the A/D converter 6 is composed of one bit indicating a sign (+ or -) and multiple digit bits indicating a numerical value.

For example, the most popular type on the market, called the 300-digit type, has an output as shown in FIG.

In other words, BJTl that displays the sign of +or -1, BIT2 that displays the presence or absence of the middle digit, and BCD of the hundreds digit.
It has BIT3 to BIT6 that display , BIT7 to BITIO that displays the BCD of the middle digit, and BIT i to BIT14 that displays the BCD of the first digit,
Outputs +19994++0 and -Q4+-1999 depending on positive and negative analog input voltages.

Therefore, when this type of A/D converter 6 is used, the measured voltage for the paid load shown in FIG. 3 can be divided by 2,000 between 0 and 19990.

However, further division is not possible.

In view of this problem, the present invention utilizes the bridge balance potentiometer of the load cell and also uses the one-symbol display part of the A/D converter, thereby doubling the measurement resolution. If there is 4,0
This paper proposes a weighing method that allows measurement in 00 divisions.

In order to achieve the above object, the present invention provides a load cell that outputs a voltage signal according to a load, a circuit that applies a bias voltage to the output of the load cell, and a circuit that converts the positive and negative output voltages of the load cell into bipolar digital values. It has a configuration that includes an A/D converter that converts the load cell, and a complement switching circuit that converts the bipolar output of the A/D converter into a unipolar output.This allows the resolution of the load cell to be increased. This is what we have come to.

An embodiment of the present invention will be described below based on the drawings.

In FIG. 5, the load cell 1, bridge balance potentiometer 3, amplifier 4, span adjustment potentiometer 5, A/D converter 6 and display 7 are the same as those in FIG. As shown in Figure 4, the sign (+o
Suppose it is a 300-digit type having a pit BITI for r-).

8 is a complement switching circuit that converts the bipolar output of the A/D converter 6 into a unipolar output, and the sign bit BIT1 is set to
II, that is, (+), the sign bit is treated as 2,000 of the numerical value bit.

and sign p) BITI is II □ II that is (
-), 1 or 9's complement is taken for the numerical bits of BIT2 of the tens digit, BCD of the hundreds digit, BCD of the tens digit, and BCD of the - digit, respectively.

Therefore, the output of the complement switching circuit 8 is the output of the A/D converter 6. +19994+10, -04-)-1999 399980000 It can be unified as a value.

Suppose now that the bridge balance potentiometer 3 is operated to move a characteristic curve such as curve A in FIG. 3 to the position of curve C in FIG. 6.

Assuming there is no tare, the negative output at zero load (
The voltage at point A in FIG. 6) is input to the A/D converter 6, and
/D converter 6 outputs a negative digital value between 10"-1999.

Therefore, the output value of the complement switching circuit 8 is a positive digital value of 2,00000000, which is the complement of the negative digital value expressed by the above formula.

Therefore, when this numerical value is displayed on the display 7, the positive digital value expressed by the above formula will be displayed at zero load.

Reference numeral 9 denotes a subtracter for compensating and zero-adjusting the positive digital value expressed by the above equation displayed by the display 7 when the load is zero.

That is, the positive digital value expressed by the above formula is stored in the memory 10 at the time of zero load, and the positive digital value expressed by the above formula in the memory 10 is subtracted from the output value of the complement switching circuit 8 during measurement. The correct measured value will be displayed on the display 7.

Reference numeral 11 denotes a storage command push button for storing the output value of the complement switching circuit 8 in the memory 10, and the output value of the complement switching circuit 8 at the time of pressing is stored.

Therefore, if the button is pressed when the load is zero, the output value of the complement switching circuit 8 at that time is stored, and the zero adjustment of the display 7 has been performed, so that the display 7 becomes zero.

Therefore, subsequent measured values are displayed correctly.

Next, if there is a tare or waste self-defense type, the value displayed on the display 7 at zero load will be the positive digital value in the above formula plus the tare or waste self-defense value, and it will be stored in the same way as above. By pressing the command push button 11, a positive compensation value corresponding to the point in FIG. 6 is stored, and subsequent measured values are displayed correctly in the same way as described above.

As described above, according to the present invention, the entire operating range of the A/D converter that converts positive and negative analog voltages into bipolar digital values can be made usable by using a circuit that applies a bias voltage to the output of the load cell. Therefore, it has the advantage of doubling the resolution of the load cell.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of an electronic weighing machine that uses a resistance wire bridge type load cell as a load detector, Figure 2 is a detailed configuration diagram of its main parts, Figure 3 is its load characteristics diagram, and Figure 4 is a bipolar weighing machine. An example of the output bit configuration of an A/D converter, FIG. 5 is a configuration diagram of an electronic weighing machine according to the present invention, and FIG. 6 is a load characteristic diagram thereof.

Claims (1)

[Claims] 1. A load cell that outputs a voltage signal according to the load, a circuit that applies a bias voltage to the output of the load cell, an A/D converter that converts the positive and negative output voltages of the load cell into bipolar digital values, and the A/D converter that converts the positive and negative output voltages of the load cell into bipolar digital values. A weighing system characterized in that it has a complement switching circuit that converts the bipolar output of a /D converter into a unipolar output, and makes it possible to increase load cell resolution.