JPH0133766B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic self-balancing electronic balance.

Generally, an electromagnetic force automatic Heihei electronic balance balances the force and load generated when electricity is applied to a force coil placed in a magnetic field, and measures the current value at that time to obtain a weight value. In conventional devices, this current value changes depending on the load being measured, so the Joule heat generated in the force coil changes depending on the weight to be measured, and the temperature of the balance mechanism also changes, resulting in poor accuracy. This has become a major obstacle when trying to obtain a high-quality electronic balance.

In contrast, the present inventors developed an electronic balance in which the amount of heat generated in the force coil is always maintained constant regardless of changes in the measured weight, whether during measurement or not, and the current supplied to the force coil generates an electromagnetic force that is in balance with the load. 0.1 by changing the direction of the current
A method has already been proposed in which the magnitude of the load is determined by alternately switching at a cycle of less than a second and calculating the amount obtained by subtracting the product of the current and time in the negative direction from the product of the current and time in the positive direction during the above cycle. There is.

According to this method, as shown in Figure 4, when the load is 0, the amount of positive current supplied (+I×t ₁ ) and the amount of negative current supplied (−I×t ₂ ) are equal, and the average current is 0
Therefore, no force is generated in the force coil.
When the load is positive, the positive current supply time t ₁ is longer than the negative current supply time t ₂ , so a positive current is supplied on average, and on the other hand, when the load is negative, t ₁
becomes shorter than t ₂ and a negative current is supplied on average. However, the amount of supply of both positive and negative currents in the period T is always maintained at a constant value regardless of changes in load, as shown by diagonal lines, and therefore the generated Joule heat does not change depending on the load.

The present invention has been made in connection with such a new type of electronic balance, and is an electronic balance in which the amount of heat generated by the force coil is maintained constant regardless of the size of the load, and which is simple in configuration and has high measurement accuracy. The purpose is to provide balances.

FIG. 1 shows a block diagram of the overall configuration of an embodiment of the present invention, and FIG. 2 shows a block diagram of the pulse width controller 5 of FIG. 1.

In FIG. 1, 1 is a weighing pan, 2 is a balance mechanism, 3 is a position detector that detects the tilt of the balance, and 4 is a weighing pan.
is a PID control controller, 5 is a pulse width controller, 6 is a positive/negative constant current generator, 7 is an up/down counter, 8
is a time clock signal generator, 9 is an arithmetic unit, 10
is the display, 12 is the force coil, 13 is the constant current source I ₀ is the feedback pulse current, I ₁ is the positive direction constant current, I ₂
is a constant current in the negative direction.

In FIG. 2, 20 is a control signal input resistor, 21 is a dynamic clock input resistor, and 22 is a control signal input resistor.
is a feedback pulse input resistor, 23 is an amplifier, 24 is an integrating capacitor, 25 is a comparator, 26 is a positive/negative constant current selector switch, 27 is a dynamic clock duty controller, 28 is a positive/negative pulse generator, S ₁
is the dynamic clock signal, S ₂ is the control signal, S ₃
is the feedback pulse signal, and _S4 is the integral output signal.

The above-described amplifier 23, integrating capacitor 24, and input resistors 20, 21, and 22 constitute an integrator 30.

Next, the operation of this embodiment will be explained with reference to the waveform diagram in FIG.

Figure a shows a control signal _S2 representing the tilt of the balance,
FIG _{. 2} is a waveform diagram showing a superimposed dynamic clock signal S1, which is a basic square wave. FIG. b is a waveform diagram showing a feedback pulse signal S ₃ having the same rise time and fall time as the current I ₀ supplied to the force coil. FIG. c is a waveform diagram of the output signal _S4 of the integrator 30. Figure d shows the output waveform K ₁ of the comparator 25,
K ₂ , which is the same as the control input signal of the up-down counter 7; Also,
The column on the right side of the figure illustrates the case of positive load, and the column on the left side illustrates the case of loaded weight.

As is clear from the figure, the dynamic clock signal _S1 is a signal having a predetermined period T and a predetermined duty ratio, in this embodiment a duty ratio of 1/2, and having the same peak value in both the positive and negative directions. Feedback pulse signal
S ₃ is a signal extracted from a part of the feedback pulse current I ₀ supplied to the force coil 12, and has the same rise and fall times as the current I ₀ and peak values in both positive and negative directions. In addition, if the period T is too long, vibration will occur, and if it is too short, the response speed of each part will become a problem.
A range of seconds is practical, and 1ms (frequency 1kHz)
degree is most preferred.

When a sample is placed on the balance pan 1, the tilt of the balance 2 is detected by the position detector 3, and the detection signal is converted into a PID control signal by the controller 4.
PID control signal 30 is sent to pulse width controller 5. In the pulse width controller 5, an amplifier 23,
Integrating capacitor 24, control signal input resistor 20, feedback pulse signal input resistor 22, and dynamic clock signal input resistor 21 operate as an integrator, and positive/negative switching is controlled by comparator 25 that determines the level of integrator output _S4 . A servo system is configured to feed back a part of the current supplied to the force coil, that is, the feedback pulse I ₀ to the integrator 30 as a feedback pulse signal S ₃ . By configuring such a servo system, the integral output signal _S4 reaches 0 volts with a delay of time Tb from the rising edge of the dynamic clock signal _S1 , as shown in figure c, and reaches 0 volts more than the falling edge of the dynamic clock signal _S1 . After a delay of time Td, it becomes 0 volt. Also, the time from when the integral output signal _S4 goes from the positive side to 0 volts until the dynamic clock signal _S1 rises.
If Tc is the time from when Ta, S ₄ becomes 0 volts from the negative side until the signal S ₁ falls, then the third
As is clear from figures a, b, and c, (-S ₁ +S ₂ +S ₃ )Ta+(S ₁ +S ₂ +S ₃ )Tb=0 (S ₁ +S ₂ -S ₃ )Tc+ (-S ₁ +S ₂ -S ₃ )Td=0 Ta+Td=Tb+Tc holds true. From the above three equations, the relational expression ∴S ₂ =S ₃ ·T ₂ −T ₁ /T is obtained. Since this feedback pulse signal _S3 is proportional to the feedback pulse current _I0 supplied to the force coil 12, the load can be determined by knowing ( _T2 - _T1 ) and T. This (T ₂ - _{T 1} ) is measured by counting the clock signal CL of the time clock generator 8 by the up-down counter 7 by alternately switching it to the up side and the down side, and based on this count value, the arithmetic unit 9 A load value is calculated and displayed on the display 10.

According to the present invention, since the amount of heat generated in the force coil is constant, after a certain period of time has passed after energization and a thermal equilibrium state is reached, even if the load to be measured changes, there will be zero point drift, sensitivity change, and other characteristic changes. It is possible to obtain a high-precision electronic balance without any problems. Additionally, it is possible to measure loads in both positive and negative directions.
Further, according to the present invention, there is no need for an A/D converter as is provided in conventional electronic balances, and the configuration is simplified because the counter simply measures the pulse width digitally. Additionally, measurement accuracy is improved by a clever configuration that incorporates weight measurement and A/D conversion mechanisms into a single servo system.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing the internal configuration of the pulse width controller 5 shown in FIG. 1, and FIGS. 3 and 4 show the operation of the above embodiment. FIG. DESCRIPTION OF SYMBOLS 1... Load pan, 2... Balance, 3... Position detector, 4... Controller, 5... Pulse width controller, 6...
...Positive/negative constant current generator, 7... Updownter, 8
... Time clock generator, 9 ... Arithmetic unit, 10
...Indicator, 12...Force coil, 25...
Comparator, 26... Positive/negative constant current changeover switch, 30... Integrator.

Claims (1)

[Claims] 1 The direction of the current supplied to the force coil that generates the electromagnetic force that balances the load is changed by a current switcher to 0.1
In an electronic balance that switches alternately at a cycle of seconds or less, and calculates the magnitude of the load by subtracting the product of the current and time in the negative direction from the product of the current and time in the positive direction during the cycle, An integrator to which a feedback pulse signal proportional to the current supplied to the force coil, a control signal representing the tilt of the balance, and a dynamic clock signal having a predetermined cycle and a predetermined duty ratio are input, and the output level of the integrator. 1. An electronic balance comprising: a comparator for determining the magnitude of the voltage based on a predetermined voltage level, and controlling the current switch according to an output signal of the comparator.