JPH0458143A - Water measuring instrument for grain - Google Patents

Abstract

PURPOSE:To measure the water of grains with high accuracy at all times by canceling the influence of temperature characteristics of the logarithmic element of a detecting circuit of an output voltage by similar temperature characteristics of the logarithmic element of an operation reference voltage setting circuit. CONSTITUTION:A circuit (a) to be measured is provided with a diode 3 as the logarithmic element and a detecting circuit A detects the electric resistance of sample grains between a couple of electrode rolls 1 and 1 as the terminal voltage across the diode 3 by logarithmic conversion. Further, a reference circuit (b) is provided and when the water is measured, the diode 3 is switched to the reference circuit (b) and circuit (a) to be measured which are connected forward through high and low constant resistances 4 and 4' alternately; and a measurement state of each measurement is compared with the reference state between two points of the characteristic of the diode 3 to correct the measurement result of the water. The operation reference voltage setting circuit B of an operational amplifier 7 has a diode 10 similar to the diode 3 of the detecting circuit A and the operational amplifier 7 is corrected automatically with the temperature characteristics of the diode 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a grain moisture measuring device for measuring the moisture content of a sample grain based on its electrical resistance.

[Prior art] Conventionally, this type of grain moisture measuring device was
The one described in Japanese Patent No. 6-41247 is known.

The device connects a pair of electrode rolls to a constant voltage power source through a constant resistor in series, and detects the current signal flowing through the sample grain sandwiched between the pair of electrode rolls as the voltage between the terminals of the constant resistor. is configured to measure the moisture content of sample grains from their electrical resistance.

[Problems to be Solved by the Invention] By the way, the electrical resistance of sample grains to moisture generally ranges from several kiloohms to several megaohms, so in the conventional moisture measuring device as described above, it is difficult to switch the measurement range. The measurement circuit is complicated, and the operation is complicated and inconvenient when measuring moisture.

Therefore, in order to measure the moisture content of the sample grain over a wide range without switching the measurement range, it is possible to compress the measurement range by logarithmically converting the resistance value of the sample grain. When a diode is used, the voltage between its terminals changes greatly depending on the temperature due to the temperature characteristics of the diode, so there are operational problems in that reference adjustment is required every time a measurement is made.

In view of the above-mentioned problems, the present invention eliminates the decrease in measurement accuracy due to the temperature characteristics of the logarithmic element, in a device that compresses the measurement range by performing logarithmic conversion using a logarithmic element, without performing reference adjustment based on temperature. Therefore, it is an object of the present invention to provide a grain moisture measuring device that can always measure grain moisture with high accuracy.

[Means for Solving the Problems] The present invention achieves the above object by having the following configuration.

In other words, the device is configured to measure the moisture content of a sample grain from its electrical resistance, and includes a detection circuit that logarithmically converts the current flowing through the sample grain using a logarithmic element and detects an output voltage, and an output of this detection circuit. A grain moisture measuring device comprising: an operational amplifier for amplifying voltage; and an operating reference voltage setting circuit for the operational amplifier having a logarithmic element equivalent to the logarithmic element of the detection circuit. be.

[Function] The grain moisture measuring device according to the present invention is provided with a detection circuit that detects the output voltage obtained by logarithmically converting the current flowing through the sample grain using a logarithmic element. The output voltage detected in response to is logarithmically transformed and the measurement range is compressed. Therefore, when measuring the moisture content of sample grains, an output voltage of a value sufficient to determine the measurement results can be obtained from a high moisture range to a low moisture range without switching the measurement range.

The device according to the present invention includes an operational amplifier that amplifies the output voltage of the detection circuit, and an operation reference voltage setting circuit for the operational amplifier that has a logarithmic element equivalent to the logarithmic element of the detection circuit. Therefore, the influence on the output voltage due to the temperature characteristics of the logarithmic element of the detection circuit is canceled by the equivalent temperature characteristics of the logarithmic element of the operating reference voltage setting circuit, and the output voltage of the operational amplifier is The moisture content of the sample grain can be measured with high accuracy from the output voltage of the operational amplifier without being affected by the moisture content of the sample grain.

[Example ] An embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, 1 and 1 are a pair of electrode rolls, and 2 is a constant voltage power supply. A circuit under test a and a pair of electrode rolls 1.1 connected in series to
Diode 3 is connected through constant resistors 4 and 4' instead of
The reference circuit that connects the f! 12, a pair of electrode rolls 1 of the circuit to be measured NA, ] and constant resistances 4, 4 of the reference circuit
' are alternately switched and connected. A detection circuit A is constituted by the circuit under test a and the reference circuit A. Constant resistance of the above reference circuit 4.
4' are high and low resistances, for example, one of them has a constant resistance of 10 megohms, and the other constant resistance 4' has a constant resistance of 1 kilohm. The constant voltage source 2 is, for example, a DC power source such as a battery with a voltage of 15 volts. 7 is an operational amplifier
The voltage across the terminals of the diode 3 to the detection circuit is inputted via the buffer 8 to the non-inverting input terminal of the operational amplifier 7. B is an operating reference voltage setting circuit B of the operational amplifier 7, and this operating reference voltage setting circuit B is as follows.
A diode 10 equivalent to the diode 3 of the detection circuit A is connected to a constant voltage power supply 2 through a constant resistor 11 of high resistance (10,000 megohms) in series, and the voltage between the terminals of the diode 10 is the same as that of the buffer 12. The circuit is configured such that the signal is inputted to the inverting input terminal of the operational amplifier 7 through the inverting input terminal. 13. +4.15.16 is operational amplification 6
7 amplification constant determining element. One power source of the operational amplifier 7 is supplied from the constant voltage power source 2. 17 is the other power supply of the operational amplifier 7.

In the grain moisture measuring device configured as described above, the detection circuit A includes a diode 3, which is a logarithmic element, in the circuit to be measured a, which is equipped with a pair of electrode rolls 1.1 for crushing the sample grain. Since the electric resistance of the sample grain between the pair of electrode rolls 1.1 is logarithmically converted and detected as the voltage between the terminals of the diode 3, a wide range of moisture can be measured in one measurement range. In addition, since the detection circuit A has a reference circuit, when measuring moisture, the diode 3
The reference circuit, which is connected in the forward direction through alternating high and low constant resistors 4.4', is alternately switched to the circuit under test a, and the measurement state is changed to the two-point difference of the characteristics of the diode 3 for each measurement. and the moisture measurement result is corrected accordingly. Therefore, there is no need to perform zero point adjustment or the like during measurement.

Furthermore, since the operational reference voltage setting circuit B of the operational amplifier 7 has a diode IO equivalent to the diode 3 of the detection circuit A, the operational amplifier 7 is automatically corrected according to its temperature characteristics by this diode IO. . Therefore, the effect on the output voltage due to the temperature characteristics of the diode 3 on the detection circuit is canceled by the equivalent temperature characteristics of the diode 10 of the operation reference voltage setting circuit B, and the output voltage of the operational amplifier 7 is It is not affected by the temperature characteristics of the sample grain, and it is possible to obtain a grain that corresponds correctly to the moisture content of the sample grain. Therefore, the moisture content of the sample grain can be measured with high precision from the output voltage of the operational amplifier 7.

Note that the output voltage S converted to the moisture content of the sample grain is the voltage between the terminals of the diode 3 when passing through the constant resistor 4 of the detection circuit A as elI, and the voltage between the terminals when passing through the constant resistor 4' in the same way. e + s The voltage between the terminals when passing through the circuit under test a is eR1. The S value when constant resistor 4 is 0, and constant resistor 4'
If the S value at the time is α, then S=a ・(eR-es/
It can be determined by e+−e@).

In FIGS. 2 and 3, the output voltage of the operational amplifier 7 is
The characteristics when converted into a digital signal by a /D converter are illustrated, and FIG. 2 shows the operating characteristics when the operating reference voltage setting circuit B of the operational amplifier 7 is not provided. Assuming that the resistance is detected from 1000 megohms to 1 kilohm, at a temperature of 20 degrees, only about 40% of the full scale capability of the A/D converter can be used, and the accuracy per bit decreases accordingly.

FIG. 3 shows the operating characteristics of the operational amplifier 7 when the operating reference voltage setting circuit B is provided. Under the same operating conditions as shown in FIG. 2, the performance is approximately 60% of the full scale of the A/D converter can be used, and the accuracy per bit improves accordingly. Therefore, even if a low-cost 8-bit A/D converter is used, moisture can be measured with sufficient accuracy.

[Effects of the Invention] As described above, the present invention provides a detection method for detecting an output voltage obtained by logarithmically converting a current flowing through a sample grain using a logarithmic element in a device that measures the moisture content of the sample grain from its electrical resistance. A circuit, an operational amplifier that amplifies the output voltage of this detection circuit, and an operation reference voltage setting circuit for the operational amplifier having a logarithmic element equivalent to the logarithmic element of the detection circuit, so it is logarithmic. In devices that compress the measurement range by performing logarithmic conversion using a logarithmic element, the moisture content of grains can always be determined with high precision by shielding the reduction in measurement accuracy due to the temperature characteristics of the logarithmic element, without making standard adjustments based on temperature. The effect of being able to measure can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a device showing an embodiment of the present invention, and FIGS. 2 and 3 illustrate characteristics when the output voltage of an operational amplifier is converted into a digital signal by an A/D converter. FIG. 2 is an operating characteristic diagram when the operational amplifier operating reference voltage setting circuit is not provided, and FIG. 3 is an operating characteristic diagram when the operational amplifier operating reference voltage setting circuit is provided. A... Detection circuit, a... Circuit to be measured, b... Reference circuit, 1.1... Pair of electrode rolls, 3. lO...
Diode, which is a logarithmic element, 7... operational amplifier, B.
・・Operating reference voltage setting circuit patent applicant Kaneko Haki Co., Ltd.

Claims (1)

[Claims] A device that measures the moisture content of a sample grain from its electrical resistance includes a detection circuit that detects the output voltage obtained by logarithmically converting the current flowing through the sample grain using a logarithmic element, and an operational amplifier that amplifies the output voltage of this detection circuit. and an operating reference voltage setting circuit for the operational amplifier having a logarithmic element equivalent to the logarithmic element of the detection circuit.