JPH0216869B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature compensation method for an electrical resistance moisture meter.

An electric moisture meter utilizes the correlation between the moisture content of an object to be measured (hereinafter referred to as a sample) and its electrical properties, such as electrical capacity and electrical resistance. However, the electrical properties of a sample vary depending on the moisture content and also vary depending on the temperature of the sample.

The magnitude of change in electrical properties due to temperature is approximately ±1.0% in terms of moisture change for a temperature change of ±10°C when measuring grain moisture using an electrical resistance method, and normally 0.1%/ Moisture temperature correction of ±1°C is performed. In order to accurately perform this temperature correction, it is necessary to detect the temperature of the sample, but in the case of an electric moisture meter that measures moisture by crushing the sample and applying pressure, it is necessary to measure a small amount of sample between narrow electrodes. Since it is difficult to insert a sensor that detects sample temperature into the sample between the electrodes, a temperature detection sensor is usually placed near the electrodes, and the moisture temperature is corrected using the detected temperature. In this method, when measuring moisture content by crushing the sample and applying pressure between the electrodes, heat is exchanged between the sample and the electrode metal, and at the time of moisture measurement, the sample temperature approaches the electrode temperature, and the initial sample temperature and electrode 1/3 of the difference from temperature
It is used as something that does not result in a large error because it is a difference in magnitude. In other words, if the initial difference between the sample temperature and the electrode temperature is 10°C, there will be a difference of about 3°C at the time of moisture measurement after crushing the sample, and even if the moisture temperature is corrected using the temperature near the electrode, the error will be about 0.3%. be. In particular, when the difference between the sample temperature and the electrode temperature is large, the sample is left to adjust to the electrode temperature before measurement.

However, in recent years, thermal drying of grains has become popular,
Grain being dried is taken out and its moisture content is measured. In such cases, the difference in temperature between the initial grain and the vicinity of the electrode is often 10°C to 20°C, making rapid measurement difficult. Because of this requirement, the moisture content of the sample taken out of the dryer must be measured immediately, but the moisture temperature correction error cannot be ignored.

The purpose of the present invention is to provide a temperature correction method that improves temperature correction accuracy by detecting sample temperature. It takes advantage of the fact that it contains information. That is, the electrical resistance value of the sample corresponds 1:1 to the moisture content if the temperature is constant, and corresponds 1:1 to the sample temperature if the moisture content is constant.

However, since the combination of the moisture content of the sample and the temperature is not fixed, it is not possible to separate the moisture content of the sample and the sample temperature from only the electrical resistance value of the sample. In the present invention, the difference between the sample temperature and the electrode temperature is known from the electrical resistance value of the sample and its change over time, the electrode temperature is measured with a temperature sensor near the electrode, and the sample temperature is essentially known. Perform moisture temperature correction based on

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

Figures 1A to 1C are examples of the electrode structure of an electrical resistance moisture meter. Figure 1A is a type in which the sample is crushed between the electrodes while pressurized, and Figure 1B is a type in which a pre-pulverized sample is applied between the electrodes. Pressure type. Figure 1C shows a type in which moisture is measured while crushing and pressurizing with a roller electrode.
In the case of the electrode structures shown in Figure 1 A and B, when the sample is pressurized between the electrodes, heat is exchanged between the sample and the electrodes.
Due to the difference in heat capacity between the electrode and the sample, the temperature of the electrode hardly changes, but the temperature of the sample approaches the temperature of the electrode. Its characteristics are shown in Figure 2.

In Figure 2, the electrode temperature is 20℃ and the initial temperature of the sample.
The graph shows that T ₀ is 30℃ for A ₁ , 20℃ for B ₁ , and 10℃ for C _1.The sample temperature approaches the electrode temperature with time, but within a few seconds, the difference between the sample temperature and the electrode temperature decreases from the initial value. This is about 1/3 of the difference. The amount of change in sample temperature increases as there is a difference between the initial sample temperature _T0 and the electrode temperature.If the sample temperature and electrode temperature are equal from the beginning, as shown in B1 in Figure ₂ , the change in sample temperature do not have.

A ₂ , B ₂ , and C ₂ in Figure 3 are the temperature-uncorrected moisture meter outputs that change over time when a sample with a constant moisture content is measured under the same conditions as A ₁ , B ₁ , and C ₁ in Figure 2. It shows the characteristic that This time change in the temperature-uncorrected moisture meter output represents a change in the resistance value of the sample, and after the initial change in resistance value due to a change in crushing pressure, it represents a change in resistance value due to a change in temperature of the sample. The temperature-uncorrected moisture output in FIG. 3 excluding the initial sample applied pressure fluctuation portion corresponds to the sample temperature change in FIG. 2, and a 1°C change in sample temperature results in a 0.1% change in the moisture meter output. Therefore, it is possible to know the change in sample temperature from the change in the moisture meter output signal without temperature correction.

Figure 4 shows the time when the sample is loaded or squeezed between the electrodes.
Starting from t ₀ , at t ₁ , t ₁ ′, and t ₂ (t ₁ < t ₁ ′ < t ₂ )
The temperature-uncorrected moisture meter output at M ₁ , M ₁ ′,
It is a characteristic diagram with _M2 . In Figure 4, A ₃ ,
B ₃ and C ₃ represent examples where the sample temperature is higher than the electrode temperature, and indicate cases where the difference between the sample temperature and the electrode temperature is large, small, and zero, respectively, and the value of M ₁ − M ₂ is the sample temperature. Corresponding to the change, the larger the difference between the initial sample temperature T and the electrode temperature T ₀ , the larger the difference, so T-T ₀
If it is proportional to , it can be approximated to first order.

That is, if T-T ₀ ∝M ₁ -M ₂ and K' is a constant of proportionality, then T=T ₀ +K' (M ₁ -M ₂ )...(1).

FIG. 5 is a characteristic diagram showing how the sample temperature changes over time. In Figure 5, when the difference between the initial temperature T of the sample and the electrode temperature T ₀ is large, the characteristic is A ₄
, and the small case is characteristic B ₄ , and the larger T-T ₀ is, the larger the change in sample temperature is.

Therefore, the sample temperature T ₂ and the electrode temperature at time t ₂
Since the difference from T ₀ becomes larger as the difference between the initial sample temperature T and the electrode temperature T ₀ becomes larger, T ₂ −T ₀ can be linearly approximated when it is proportional to T − T ₀ .

That is, T ₂ −T ₀ ∝T−T ₀ . Add to this the first
Substituting the formula, T ₂ −T ₀ ∝K′(M ₁ −M ₂ ) ……(2) Therefore, the second equation becomes T ₂ =T ₀ +K(M ₁ −M ₂ ) ……(3) It can be approximated as

Here, K is a proportionality constant determined by the structure and material of the electrode, the type of sample to be measured, etc. In order to obtain a more accurate sample temperature T ₂ , T ₂ is given by a higher-order expression of M ₁ −M ₂ . Note that the electrode temperature T ₀ is detected by installing a temperature sensing element near the electrode.

Even if the sample temperature and electrode temperature match and there is no time variation in the temperature-uncorrected moisture meter output as shown in C ₃ in Figure 4, it is not necessary to wait until t ₂ o'clock. accordingly
Temperature uncorrected moisture meter output at t ₁ ′ (t ₁ < t ₁ ′ < t ₂ )
Measure M ₁ ′ and compare this M ₁ ′ with the temperature-uncorrected moisture meter output M ₁ at t _1. If the difference is within a certain range, it is determined that the sample temperature and electrode temperature match. , temperature uncorrected moisture signal _{M 1 or}
Correct M ₁ ′ to obtain the moisture content value. At this time, if the temperature-uncorrected moisture signals match on the order of 0.01%, it is sufficient in terms of measurement accuracy even if it is determined that the sample temperature and electrode temperature match.

FIG. 6 is a block diagram of one embodiment of an electric moisture meter for realizing the temperature correction of the present invention, in which a timer in a microprocessor section 6 is started by the sample set switch means 4 which notifies that a sample has entered the electrode. After Δt time, at t ₁ , the transfer switch 8A is closed, and the signal from the electrode section 1 is linearized, level adjusted, etc. in the conversion section 2, and is input to the A/D converter 5, where it is A/D converted. The converted digital signal is read by the microprocessor 6 and processed as data.
Let D be ₁ . Furthermore, at time t ₁ ′, a signal from the electrode is also read and set as D ₁ ′. If the signal converter 2 is designed so that the data D ₁ , D ₁ ′ represent the temperature-uncorrected moisture signals M ₁ , M ₁ ′, the data D 1 , D 1 ′ are directly converted into the data D 1 , D ₁ ′. ₁ ' is calculated using a predetermined moisture conversion formula to obtain temperature uncorrected signals M ₁ and M ₁ '.
Also, close the transfer switch 8B, input the electrode temperature signal from the temperature detection section 3 to the A/D conversion section 5,
The output is read by the microprocessor 6 to obtain electrode temperature data _T0 . If the difference between M ₁ and M ₁ ′ is within a certain width, it is determined that the sample temperature and the electrode temperature are equal, and the temperature-uncorrected moisture signal is determined at the electrode temperature T ₀ .
Calculate the moisture content value by correcting M ₁ or M ₁ '. _{M1
If the} difference _between Here, the microprocessor 6 is broadly defined as an input/output port,
Including ROM, RAM, etc. Also, time t ₁ is after the start of measurement.
If the time is about 0.5 seconds, t ₁ ' is after another 0.5 seconds, and t ₂ is after another 1 to 2 seconds, the moisture measurement time can be several seconds.If the sample temperature and electrode temperature are close, the measurement can be done in about 1 second. become. The switches 8A and 8B are analog switches with gates. The microprocessor 6 uses these data M ₁ , M ₂ , T ₀ and a predetermined constant K to calculate T 2 = T ₂ =
Calculate T ₀ +K(M ₁ −M ₂ ).

This sample temperature _T2 , temperature uncorrected moisture signal _M2 , and predetermined temperature correction coefficient (0.1%/1℃)
Calculate the temperature-corrected moisture content M of the sample using the following formula: M=M ₂ −α(T ₂ −20) (4). α is a constant determined by the type of sample, etc.

Here, the temperature correction is based on 20°C, and the uncorrected temperature moisture signal _M2 is sent to the signal converter 2 so that it directly indicates the moisture content of the sample when the sample temperature is 20°C.
An arithmetic expression for the output level or the moisture uncorrected signal M ₂ from the read data D ₂ by the microprocessor 6 is designed. This temperature-corrected moisture content M of the sample is output to the moisture display device 7.

FIG. 7 is a flowchart illustrating the above operation. Here, the delays of t _A , t _B , and t _C seconds may each be about 0.5 seconds.

According to the temperature correction method of the present invention, it is possible to correct the true moisture content based on the sample temperature, and it is possible to measure the moisture content with less error for grains that are hot during thermal drying, and to prevent grains from being overdried or A great effect can be obtained in that it can be finished to have an appropriate moisture content without drying.

Similarly, even if the temperature of the sample and the electrode are different, it can be measured immediately, and if the temperature of the sample and the electrode are almost the same, the moisture can be measured quickly, and the measurement can be made without much difference from the conventional sense of time.

[Brief explanation of drawings]

Figure 1 A to C are diagrams each showing an example of the sample electrode structure of a moisture analyzer, Figure 2 is a characteristic diagram of time versus sample temperature, and Figures 3 and 4 are time versus temperature based on experimental data. The characteristic diagram of the uncorrected moisture meter output, Figure 5, is
A characteristic diagram of time versus sample temperature, FIG. 6 is a block diagram of an embodiment of a temperature correction device for a moisture meter for carrying out the present invention, and FIG. 7 is a flowchart for explaining an embodiment of the present invention. E...Sample electrode, G...Sample, 1...Sample electrode, 3...Temperature detection element, 4...Sample set switch, 8A, 8B...Transfer switch, 6...Microprocessor, 7...Moisture display Device.

Claims (1)

[Claims] 1. In a temperature correction method for an electrical resistance moisture meter in which the temperature of the object to be measured is balanced with the temperature of the measurement electrode section, the time point t ₀ when the object to be measured is loaded or clamped on the electrode section. t ₁ , t ₁ ′, after different fixed times from
The electrical resistance of the object to be measured is measured multiple times at t ₂ (t ₁ < t ₁ ′ < t ₂ ) to obtain a temperature-uncorrected moisture signal, and the difference between the temperature-uncorrected moisture signals at t ₁ and t ₁ ′ is calculated. is below a predetermined value, it is determined that the temperature is in the above-mentioned state of equilibrium, and the temperature is corrected using that electrode temperature; otherwise, t ₂
Measure the electrical resistance of the measured object at t, obtain a temperature uncorrected signal, and calculate the difference in temperature uncorrected moisture signal between t ₁ and t ₂ .
Estimation formula T ₂ based on time vs. temperature uncorrected moisture signal characteristic data obtained in advance for M ₁ −M ₂ and electrode temperature T ₀
T ₂ = T ₀ + K (M ₁ - M ₂ ) Find the temperature of the measured object at t ₂ , and based on those temperatures, calculate the temperature of the uncorrected moisture signal at t ₁ or t ₂ . Temperature correction method for electric resistance moisture meter.