JPH0311429B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention places a pair of electrodes inside a subject,
The present invention relates to a moisture content measuring device that measures the moisture content of a sample such as grain using the dielectric constant between the electrodes, and particularly relates to a moisture content measuring device that compensates for errors based on the bulk density of the sample.

As a device for measuring the moisture content of grains, etc. by compensating for errors based on bulk density, for example, two pairs of electrodes are placed inside the grain, and two oscillation circuits each using an oscillation capacitor are used to measure the moisture content of grains. There is one that oscillates different frequencies and calculates the moisture content from the ratio of each oscillation frequency.

This device has two types of oscillation frequencies: the moisture content is proportional to the dielectric constant between the electrodes, and this dielectric constant is proportional to the oscillation frequency applied between the electrodes, resulting in the moisture content being proportional to the oscillation frequency. Taking advantage of the fact that the bulk density of the sample remains almost constant with respect to changes in the dielectric constant ratio, moisture content can be determined based on two types of oscillation frequencies when grains with the same bulk density are sandwiched between electrodes. It is designed to perform measurements.

In other words, as shown in Fig. 3, the relationship between the dielectric constant ratio at two types of oscillation frequencies and the moisture content of the specimen is approximately constant regardless of the bulk density of the specimen. The moisture content of the sample can be measured from the ratio of dielectric constant to frequency without being affected by bulk density. In addition, Figure 3 above shows that the bulk density of the high-density specimen is about 10% compared to the low-density specimen.
The temperature was raised and measured at room temperature.

However, in the above measuring device, the electrodes are
In addition, since the bulk densities between the electrodes are not necessarily the same, the configuration of the measuring section becomes complicated and accurate moisture content measurement cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a measuring device having a simple configuration of a measuring section and capable of accurately measuring moisture content.

To summarize this invention, a pair of electrodes are placed inside the subject, and these electrodes are used as a shared oscillation capacitor to connect two oscillation circuits.
Different frequencies are oscillated, the oscillation circuit is alternately driven by a switching circuit, each oscillation signal is placed on one transmission line, and the receiving side demodulates the signal by a filter means, and the demodulated 2 The method is characterized in that two types of frequencies are determined by calculation from the different types of frequency signals and the switching times of both signals, and then the moisture content is determined from the collection number.

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

FIG. 1 is a block diagram of a grain moisture content measuring apparatus according to an embodiment of the present invention.

In the figure, the upper and lower electrodes of a capacitor C1 (oscillation capacitor) are arranged in a hopper that stores grains. A capacitor C2 connected to the capacitor C1 and coils L1 and L2 constitute a resonant circuit 1 together with the capacitor C2. The resonance circuit 1 constitutes an oscillation section of a first oscillation circuit 2 and a second oscillation circuit 3. The oscillation driving section of the first oscillation circuit 2 includes an amplifier 20 having a positive feedback loop, a detection circuit 21 that detects the oscillation output, a comparison circuit 22 that compares a switching signal τH and the output of the detection circuit 21, which will be described later. Amplifier 2 with the comparative output at the specified level.
It is composed of an amplifier 23 that controls the drive time of 0. Further, the oscillation drive section of the second oscillation circuit 3 is composed of an amplifier 30, a detection circuit 31, a comparison circuit 32, and an amplifier 33, similarly to the first oscillation circuit 2.

The reactance of the coil L1 of the resonant circuit 1 is set to be much larger than the reactance of the coil L2. Therefore, the oscillation frequency f1 of the first oscillation circuit 2 is 1/(2π√22(1+2)), and the oscillation frequency f2 of the second oscillation circuit 3 is 1/(2π√1(1+2)). Become.

That is, the resonant circuit 1 serves as the resonant parts of two oscillation circuits, and causes the first oscillation circuit to oscillate a relatively high frequency, and causes the second oscillation circuit to oscillate a relatively low frequency.

The two oscillation circuits 2 and 3 are alternately switched and driven by a multivibrator 4 constituting a switching circuit. This multi vibrator 4
The outputs of both stages are applied to comparison input terminals of comparison circuits 22 and 32 as τH and τL, respectively. As mentioned above, the comparison circuits 22 and 32 compare the signals τH and τL with the outputs of the detection circuits 21 and 31, but since the comparison outputs are output only when both levels are the same, the oscillation circuit 2 and 3 are oscillation frequencies f1, which are relatively high frequencies while being alternately switched and driven at times τH and τL, respectively;
The oscillation frequency f2, which is a relatively low frequency, is output in a time-division manner.

The high frequency signal fH (oscillation frequency f1) and the low frequency signal fL (oscillation frequency f2) are sent to the V-converter 2.
4, 34 performs voltage-current conversion, and capacitor C3
and is placed on the transmission line 5 via the capacitor C4. The transmission line 5 is composed of a coaxial cable, and also serves as a power supply line for supplying voltage to the oscillation circuits 2 and 3. That is, the transmission line 5 simultaneously supplies voltage to the oscillation circuits 2 and 3 and transmits two oscillation signals. Filter 6
is provided to extract only the power supply voltage from the transmission line, since the power supply voltage and two oscillation signals are superimposed on one line in this way. Constant voltage power supply circuit 7 connected to filter 6
is provided to stabilize oscillation and prevent measurement errors.

On the receiving side of the transmission line 5, the oscillation circuit 2,
A power supply E for supplying voltage to the circuit 3 and a capacitor C5 for extracting only the signal are connected.
The DC component cut signal is made to an appropriate level by an amplifier 8, and further demodulated by a filter 9 into the original high frequency signal fH and low frequency signal fL. Each demodulated signal is sent to an envelope detection circuit 10,
11 and counters 12 and 13, and an envelope delayed signal obtained by delaying the envelope signal in delay circuits 14 and 15 is guided to reset terminals of the counters 12 and 13. The counters 12 and 13 count the high frequency signal fH and the low frequency signal fL while repeatedly being reset at the falling edge of the envelope delay signal. Therefore, the counters 12 and 13 hold the results of counting the signals fH and fL during the switching times τH and τL, respectively. Registers 16 and 17 are counters 12 and 13
The stored contents are latched at the falling timing of the envelope delay signal, and the contents are output to the microcomputer 18, which is an arithmetic means.

FIG. 2 is a signal waveform diagram of the main parts of the measuring device having the above configuration. As shown in the figure, the high frequency signal fH is generated only when the signal τH is high, and the low frequency signal fL is generated only when the signal τL is high.
Therefore, if we count the number of oscillations when the signals τH and τL are high, we can calculate the number of oscillations and the signals τH and τL.
The frequencies of the signals fH and fL can be found from the time when the signal is high. The microcomputer 18 is
The frequency is calculated from the values set in the registers 16 and 17 and the switching time obtained from the envelope signal, and the moisture content is calculated based on the frequency value.

This calculation calculates the frequency variation coefficient for changes in bulk density by a (high frequency variation coefficient of about 10MHz) and b (1M
This is done by executing the following formula as the low frequency variation coefficient (of the order of Hz). Note that these coefficients are stored in advance in the microcomputer.

p (moisture content) = (a・fH)/(b・fL) As described above, in this example, the high frequency and low frequency oscillation circuits are driven alternately using the same oscillation capacitor, and the driving time is The frequency is determined by counting the number of oscillations, and the moisture content is determined from that frequency. Normally, the switching time for alternately driving the oscillation circuits 2 and 3 is set to be very short with respect to the movement of the grain that is the subject. This allows both high and low frequencies to be measured when the grain condition is fixed. That is, only one set of electrodes is used, but two different frequencies are measured under the same conditions. Therefore, the measuring section becomes simple and measurement errors do not occur. Moreover, since a single transmission cable is used to supply voltage to the oscillation circuits 2 and 3 and to transmit the oscillation signal, there is an advantage that wiring is simple.

The oscillation period of the multivibrator 4 is determined by a CR constant of a time constant circuit (not shown), but the drive time of each oscillation circuit 2, 3 may be made different by changing the CR constant. Alternatively, the transmission line 5 may be used exclusively for oscillation signals, and a power supply line may be provided separately.

As described above, according to the present invention, since only one oscillation capacitor is used, the configuration of the measurement section is simplified, and there is no need to make any modifications to the electrode arrangement within the subject. Changes over time affect both oscillation frequencies at the same rate, which has the effect of reducing errors caused by changes in the electrode portion over time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a grain moisture content measuring apparatus according to an embodiment of the present invention. FIG. 2 is a signal waveform diagram of the main parts of the device. Further, FIG. 3 is a diagram showing the relationship between the ratio of dielectric constants at two types of oscillation frequencies and the moisture content of the specimen, and shows the basis of the measurement method that is the premise of this invention. 1...Resonance circuit, 2...First oscillation circuit, 3...
...Second oscillation circuit, 4...Multivibrator (switching circuit), 5...Transmission line, 9...
Filter (for demodulation), 18...microcomputer, C1...oscillation capacitor.

Claims (1)

[Claims] 1 A pair of electrodes placed inside the subject, an oscillation circuit with two types of frequencies that configures an oscillation capacitor with these electrodes, a switching circuit that alternately switches and drives this oscillation circuit, and two outputs of the oscillation circuit. filter means to demodulate the received signal after transmission to the original oscillation output, and to obtain the above two types of frequencies from the demodulated oscillation output and switching time, and to determine the moisture content based on the frequency values. A moisture content measuring device comprising: arithmetic means for determining .