JPH0424656B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance moisture meter used for detecting the moisture content of grain.

This type of moisture meter includes a fixed electrode and a movable electrode that faces the electrode and can be approached and separated by a motor drive,
The moisture content is electrically detected by crushing the grains interposed between the two electrodes by moving the electrodes, and converting the resistance change between the two electrodes into a DC voltage using the resulting moisture.

Such moisture meters are widely used today, for example, to detect the dry state of grain in dryers, but the output between the electrodes may vary depending on the number or thickness of grains interposed between the electrodes, even though they have the same moisture content. The disadvantage was that the voltage fluctuated, causing measurement errors.

Therefore, the present invention aims to improve the above-mentioned drawbacks of the prior art, and its purpose is to provide a moisture meter that can accurately measure water content by correcting variations in inter-electrode output due to grain number or grain thickness. be.

A feature of the present invention for achieving this object is that the resistance moisture meter is equipped with a motor-driven opposing electrode 1 that can be moved in close contact and separation, and that crushes grains with the electrode 1 and electrically detects the moisture content thereof. The resistance type moisture meter is provided with a correction circuit 3 for correcting the output between the electrodes 1 in accordance with the load current of the motor M, and corrects fluctuations in the output between the electrodes due to the number or thickness of grains to be crushed.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a resistance type moisture meter according to the present invention, in which reference number 1 is a counter electrode of the moisture meter, 3 is a correction circuit for correcting the electrode output according to the load current of the electrode moving motor M, and 5 is a correction circuit for correcting the electrode output according to the load current of the electrode moving motor M. An abnormality signal generation circuit 7 outputs an abnormal signal when the load current of the motor M is extremely small; and 7 is a circuit for controlling the drive of the electrode moving motor M, and also performs output processing of the correction circuit 3 in consideration of the abnormality signal. This is a control unit including a computer.

The counter electrode 1 has a fixed electrode 1a and a moving electrode 1b, and the moving electrode 1b can be moved toward and away from the electrode 1a by a motor M, and the grains interposed between the electrodes are crushed by the electrode movement. Therefore, the load current of the electrode moving motor is approximately proportional to the number or thickness of grains interposed between the electrodes.

The correction circuit 3 is an operational amplifier 3 having a feedback resistor R.
0, and the electrode output voltage Vs is applied to its negative input via the first variable resistor _R1 , and the load voltage Vm of the motor M is applied via the second variable resistor _R2 . The load voltage Vm of the motor M is given by a DC voltage conversion circuit consisting of a current transformer CT, a diode D, and a capacitor C that detects the load current of the motor M. Note that the + input of the amplifier 30 is at ground potential.

The abnormal signal generating circuit 5 has a comparator 50, whose negative input is given a reference potential obtained by dividing the voltage between resistors γa and γb, and the positive input is applied with the load potential Vm of the motor M. If the load voltage Vm is extremely low during the crushing of grains for moisture detection, there are no grains between the electrodes and it is virtually impossible to detect moisture, so the abnormal signal generation circuit 5 detects this state by comparing it with a reference voltage and outputs an abnormal signal.

Fig. 2 is an explanatory diagram of the operation of the circuit shown in Fig. 1. As is clear from the figure, the electrode output voltage Vs decreases as the number or thickness of grains to be measured decreases even when the water content is the same. It can be seen that measurement errors occur regardless of the situation. The purpose of the present invention is to correct such measurement errors using a correction circuit to provide a substantially constant output voltage Vo regardless of the number of grains or the size of grain thickness.

The operation of the circuit shown in FIG. 1 will be explained below with reference to FIG. 2.

As shown in FIG. 2, as the number of grains or grain thickness increases, the electrode output voltage Vs decreases, but the load voltage Vm of the motor M increases almost correspondingly to the decrease. Therefore, by appropriately determining the circuit constants of the correction circuit 3, it is possible to make the output voltage substantially constant regardless of the number of grains or grain thickness. This will be explained more specifically below.

In FIG. 2, assuming that the electrode output voltage Vs and the motor load voltage Vm satisfy substantially linearity, the following equation holds true.

Vs=-ax+b...(1) Vm=cx+d (a, b, c, d are constants obtained from experimental values) Also, assuming that the amplification degree of the amplifier 30 is 1∞, the output voltage Vd is finite. As long as the input voltage is O, the first and second variable resistors (R ₁ , R ₂ )
The respective currents flowing through the resistor R flow in a superimposed manner. Since the input voltage is O, the output voltage Vd is expressed by the potential across the resistor R, and the following equation holds.

Vd=−R(Vs/R ₁ +Vm/R ₂ )...(2) The following equation is obtained from equations (1) and (2).

Vd=-Rx{x(c/ _R2 -a/ _R1 )+(b/ _R1 +
d/R ₂ )} ...(3) Therefore, if (c/R ₂ - a/R ₁ ) in equation (3) is made zero by adjusting the first and second variable resistors, Vd remains constant. It is clear that this will happen. Note that if the linearity of the electrode output voltage Vs is not fully satisfied, the linearity can be compensated for by a linearizer.

The output voltage Vd thus obtained is almost independent of the number of grains or grain thickness, as shown in FIG. 2, and is given to the control section 7. In addition,
If the control section 7 cancels the moisture information corresponding to the above abnormal signal when it is given, more accurate moisture information can be obtained.

As explained above, according to the present invention, since the electrode output voltage is corrected according to the load current of the electrode moving motor, the detected voltage that is unrelated to the number or grain thickness of grains interposed between the electrodes can be adjusted. you can get
Therefore, it becomes possible to provide a more accurate resistance type moisture meter.

[Brief explanation of drawings]

FIG. 1 is an embodiment of a resistance type moisture meter according to the present invention, and FIG. 2 is an explanatory diagram of the operation of FIG. 1. 1... Counter electrode, 2... Correction circuit, M... Electrode moving motor.

Claims (1)

[Claims] 1. In a resistance moisture meter that is equipped with opposing electrodes that can be moved toward and away from each other by driving a motor, and that crushes grains with the electrodes and electrically detects their water content, the output between the electrodes is corrected according to the load current of the motor. A resistance-type moisture meter that is equipped with a correction circuit to correct variations in output between electrodes depending on the number or thickness of grains to be crushed.