JPH02147837A - Optical concentration meter - Google Patents

Abstract

PURPOSE:To easily compare measured values of optical concentration meters with each other even when kinds of plants or measuring conditions of each meter are different from each other by providing a controlling arithmetic circuit and input device which corrects stored operation factors and offset values. CONSTITUTION:This optical concentration meter finds the concentration of a specific substance contained in a sample from the difference in absorption coefficient (difference in absorbance) between the light of a waveform band strongly absorbed by the specific substance and the light of a waveform band weakly absorbed by the substance. A controlling arithmetic circuit 21 controls each circuit and, at the same time, calculates the concentration of the substance from the difference in absorbance by using a prescribed calculation formula. An input device 10 is constituted of three switches and used for correcting operation factors and offset values as well as for switching the mode to the operation factor setting mode. Therefore, the same chlorophyll concentration can be shown even when kinds of leaves are different from each other, by, for example, correcting the concentration meter so that the same display value can be shown against the same nitrogen concentration.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention irradiates a sample with light in two specific wavelength ranges, measures the amount of light after the two lights have passed through the sample, and measures the light intensity. This relates to an optical densitometer that measures the concentration of a specific substance contained in a sample based on the difference in the concentration of the substance.

(Prior Art) Chlorophyll meters have come to be used as two types of optical densitometers to easily measure the chlorophyll concentration of fresh leaves for investigating the growth status of crops. This device has the characteristic that chlorophyll exhibits a high absorption rate for light in the blue and red regions, a low absorption rate for light in the green region, and particularly almost no absorption in the infrared region. Taking advantage of the fact that there is
- Select two wavelengths of light that have different absorbances for fresh leaves from the above wavelength range, determine the transmittance of the two lights for fresh leaves, and determine the chlorophyll concentration from the difference in the transmittance of the two lights. The measurement light usually uses light in the red region (R), where chlorophyll has strong absorbance and is not affected by carotene (yellow pigment), and infrared region (IR), where there is almost no absorption by chlorophyll.

Now, let the outputs when the light from the light source in the red region (R) and infrared region <IR,) directly enter the light-receiving element be for and I oir, respectively, and each of the above lights is received through the leaf of the sample. The output when measured by the element, people Ir, I
If ir, then the following equation holds true.

I ir= I oir , F ir −10”'d”
I r = I or-Fr -10-""'However, C
C; Chlorophyll concentration in the leaf α; Extinction coefficient of chlorophyll in the R range αir: Extinction coefficient of chlorophyll in the IR range Fr Light transmittance of substances in the leaf other than chlorophyll in the HR range Fir Light transmittance of substances in the leaf other than chlorophyll in the HIR range From the above equation for the light transmittance of the substance, the following equation (1) can be obtained.

Log(Ior/Ir) −Log(Ioir/
I 1r) = Cc (ar - a effect) - (Log
Fr -LogFir)...(1) The left side of equation (1) is determined by measuring the amount of light, the extinction coefficient of the first term on the right side is known as it is a direct characteristic of chlorophyll, and the second term is The term is determined by the type of plant and whether it is young or fresh leaves, etc.
Once the type of plant and the appropriate age after germination are determined, it is a constant, so
The chlorophyll concentration Cc can be determined from equation (1).

The chlorophyll meter measures Ior and Ioir in the above equation (1) without inserting the sample, measures Ir and Iir with the sample inserted, and calculates the chlorophyll concentration C (by equation (1)). Conventionally, red light emitting diodes and infrared light emitting diodes have been used as light sources in the , R, and IR regions.

Since the light used in this case is not monochromatic, αi and α
Since ir is data regarding monochromatic light, it cannot be used as is and has only an approximate meaning. Therefore, it is necessary to include (αr - αir) in equation (1) in the measurement sensitivity, create a calibration curve using data measured using samples with known chlorophyll concentrations, and determine the concentration from this calibration curve. Should. However, in reality, the absolute concentration of chlorophyll is not necessary;
It is sufficient to know the relative concentration with respect to the reference leaf, and in that case, (α'-αir) in equation (1) has only the meaning of the gain of the photometric circuit, and the second right-hand side of equation (1) This term can be canceled out by appropriately adjusting the offset of the photometric circuit.For this reason, manufacturers use two filters of appropriate gradation and lightness in place of the leaves, and adjust the gain and offset of the photometric circuit appropriately. Therefore, the manufacturer adjusts the device as shown below before shipping it.

When formula (1) is transformed, +LogF r -LogF 1r)---(A)
Or, zero point tone! (offcent), the left side of equation (a) = 0, L
An optical filter f1 with ogFr = LogFir (=O) is inserted and measured, and adjustment is made so that S rl+ a = O (determine offset a).

In gain adjustment, C=Cf, ar=Br, a
Measure using the optical filter f2 of irBir, LogFr-LogFir (=0), and adjust from the measurement result Sr2 so that bsf2=Cr (Br-Bir)=---(1) (gain coefficient ).

In this way, the offset a and the gain 1 series coefficients are set, and adjustments are made so that the optical density value can be calculated on the circuit according to the formula from the measured value.

For this reason, during production adjustments, manufacturers adjust the offset a and gain coefficient A so that the same model of equipment shows the same value for the same material, and then fix it before shipping. When measuring the same sample using two devices of the same model, they may not show the same values. When the sample leaves are located in a large area or are scattered in various locations, it is necessary to use many of the same models for measurement.In this case, even if the relative concentration of chlorophyll is the issue
It is necessary that each device be calibrated to give the same measurements for the same sample. As mentioned above, the reason why the indicated value varies depending on the device is due to the two wavelengths r and i used.
The wavelength distribution of the light source and the spectral sensitivity of the photodetector for r use differ slightly depending on the device, and when adjusting, the readings are simply adjusted so that they match at two specific points. This is thought to be because if the range differs from what was assumed during factory adjustment, differences in the characteristics of each device will become apparent.

This is because the spectral characteristics of transmittance and absorption 1 series change depending on the leaf and situation being measured.If the off-cella 1 to a and gain coefficients of the photometric circuit are set as fixed values as in the past, the actual measurement In this case, there was a problem in that measurement values between devices of the same model could not be compared due to variations in spectral characteristics for each measurement.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems, and when measuring using multiple devices, even if the types of plants are different or the measurement conditions change, the problems between the devices can be improved. The purpose is to allow the user of the device to calibrate it as appropriate so that the measured values can be compared.

(Means for solving the problem) The concentration of a specific substance in a sample is determined by the difference in absorbance between light in a wavelength range where absorption is large by the specific substance and light in a wavelength range where absorption is small by the substance (absorbance difference). In the optical densitometer determined by Established.

(Function) The present invention includes a means for switching to arithmetic coefficient setting mode and an input device for correcting an offset value and a gain coefficient,
This allows the user to freely correct the offset value and gain coefficient. When a user corrects the offset value and gain coefficient, in practice, the chlorophyll concentration can be determined from the nitrogen concentration, and the nitrogen concentration contained in leaves can be measured using various methods. It's easy to do. By using this nitrogen concentration as a reference and correcting it so that the same displayed value is displayed for the same nitrogen concentration, it is possible to easily display the same chlorophyll concentration even if the types of leaves are different.

Moreover, if the spectral absorption characteristic spectrum of a leaf can be measured using a spectrometer, more accurate adjustment can be made by correcting the offset value and gain coefficient using the obtained spectrum data.

In addition, if the user can freely correct the offset value and gain 1 series, it will be possible to adjust the measurement sensitivity of multiple measurement devices to the same level, and measurement errors in data obtained with different measurement devices will be significantly reduced. be done.

(Example) FIGS. 1 and 2 show a plan view and a side view of an example of an optical densitometer (chlorophyll meter) of the present invention. In Figures 1 and 2, 1 is a sample stand on which a leaf as a sample is placed, 2 is a rotating plate, and the end portion 2b is pivotally attached to the upper part of the sample stand 1 with a bottle 3, so that it can be moved up and down. It is possible to open with a spring (not shown).
upper) direction. 4 and 5 are light emitting diodes which are light sources that generate light in the red region and infrared region, and are provided adjacent to each other in a direction perpendicular to the rotation direction in a recess on the lower surface of the movable end portion 2a of the rotation plate 2. There is. Reference numeral 6 denotes a light receiving element, and the light emitting diode 1 is mounted on the upper surface of the tip 1a of the sample stage 1.
, 5. Reference numeral 7 is a holding plate provided on the upper surface of the tip portion 1a of the sample stage 1 to cover the light receiving element 6 and holds the sample; 8 is a display unit that displays calculation coefficients and measurement results; 9 is a power switch; and 10 is an input device. sWl, SW2
．． It is composed of SW3 and is used for both switching to the calculation coefficient setting mode and correcting the calculation coefficient. 11
12 is a finger holding recess provided on the upper surface of the rotary plate 2, and 12 is a hold grip for holding the chlorophyll meter. A sample fixing section 13 is constituted by the light emitting diodes 4 and 5, the light receiving element 6, the holding plate 7, the sample stage 1, and the tips 1a and 2a of the rotating plate.

FIG. 3 is a block diagram showing the circuit configuration of the chlorophyll meter. In the figure, reference numeral 21 is a sub-leg calculation circuit that controls each circuit and performs various calculations related to measurement, and 22 is an E-D drive circuit that controls on/off of the red light emitting diode 4 and the infrared light emitting diode 5. , 23 is the re-emitting diode 4 to compensate for temperature-induced changes in properties.
, 5 and a temperature measurement circuit for measuring the temperature of the light receiving element 6, 2
4 is a current-voltage conversion circuit that converts the photocurrent output of the light-receiving element 6 into a voltage signal and amplifies the signal; 25 is an AD2 converter that converts analog signals from the temperature measurement circuit 23 and current-voltage conversion circuit 24 into digital signals; The circuit 26 consists of a dip switch and an EEPROM, and the calibration value is set according to the characteristics of each circuit.
Arithmetic coefficient and light emitting diode 4 input using 0
．． 5, a calibration value storage circuit that stores information regarding the amount of light emitted, the peak wavelength, and the temperature characteristics of the light receiving output of the light receiving element 6; 27, a warning circuit that notifies the suitability of initial calibration and measurement with a buzzer;
28 reads the state of the switch 29 and sends it to the control calculation circuit 2.
1 is a switch input circuit, and 30 is a display element drive circuit that controls a display element 31 that displays measured values and the like. Each circuit is connected to a power supply circuit via a power switch.

The operation and operation of the above-mentioned device will be outlined. For normal measurements, turning on the power switch 9 puts the device operation into an initial calibration mode. This mode is a mode that measures for and Ioir in equation (1) above without inserting a sample. When the operation in this mode is finished, a buzzer sounds to announce the end of the calibration mode, and the operation mode is changed to the measurement mode. replaces. Then, the user opens the rotating plate 2, places the sample on the sample stage 1, and closes the rotating plate 2. There is a measurement switch that is linked to the opening and closing of the rotating plate 2.
It turns on when you close it, and the sample transmitted light I r, r ir
is measured, calculations based on equation (1) are performed, the chlorophyll concentration is displayed on the display section 8, and the operation 1t returns to the beginning of the measurement mode. Therefore, the user can subsequently measure samples one after another. That is, when you turn on the power switch 9, it will automatically enter the initial calibration mode, for
After measuring Ioir, it automatically enters the sample measurement mode. In the measurement of for etc., for light source 4.5,
Since there is only one light-receiving element 6, the control arithmetic circuit switches to first measure red light, then measure infrared light. The input device 10 is used when a user performs user correction to correct the values of the gain coefficient and offset a previously set in the device. Three modes are available for user correction. There are three types of modes: a coefficient mode that corrects only the offset a, an offset mode that corrects only the offset a, and an r thread count and offset mode that corrects both b and a.
W 1 , offset mode is switch SW2. The coefficient and offset modes are activated by pressing the switch SW3, and if you turn on the power switch 9 while pressing any of these switches depending on the purpose, the device will change its operation f.
j mode is set. At the same time, the previously set coefficient or offset la is displayed on the display section 8. In the subsequent steps, SW2 increases the set value by 1 unit each time you press it, and SW3 decreases the set value by 1 unit each time you press it.The corrected value is displayed on the display 8, so you can set it at an appropriate location. When switch SW1 is pressed, SWI operates as a write switch, and the corrected coefficient or offset is written into the calibration value storage circuit 26 in place of the previous value, and then the operating mode automatically changes to the normal measurement mode. In other words, when the offset value of the corrected coefficient equation is written into the storage circuit 26, the operation enters the initial calibration mode. The operation of each mode will be explained in detail below.

The user correction operation, which is the gist of the present invention, will be explained. Normally, when the power is turned on, the processing shifts to the initial calibration mode and the measurement mode, but when correcting the calculation coefficients, the mode is switched to the setting mode. To change the mode, turn on the power switch 9 while pressing any one of SW1 to SW3 of the input device 10 when the power is turned on. In this case, turn on the power switch 9 while pressing SW1. SW2 allows switching to "coefficient" setting mode, SW2 switches to "offset" setting mode, and SW3 switches to "coefficient and offset" setting mode. FIG. 4 shows a flowchart 1- of offset setting mechanical cutting. In this case, the operation starts when SW2 is pressed and the power is turned on. In #A1, the offset value currently stored in the calibration value storage circuit 26 is displayed on the display section 8. This remains 0 unless previously set by the user. #A2, SW
Determine whether l has been pressed. In the case of user correction, the operation shifts to #A8 operation although SW1 is not pressed at first. If you want to increase the set value, press SW2, if you want to decrease it, press SW3, and in the program, press #A3.
Determine whether W2 is pressed, and if it is pressed, #A5
, the offset value is increased by 0.1, and the added offset value is displayed in #A7. If SW2 is not pressed, determine whether SW3 is pressed in #A4,
If it is pressed, move to #A6 and set the offset value to 0°1
Display the subtracted offset value.

If it is not pressed, return to #A2 and check the input of switch SW1 again. While going through the loop from #A2 to #A7 in this way, the offset value (#A7) changed by the measurer is checked on the display section 8, and when it reaches the desired value, the measurer Press SWI, so #A2 is set to Y.
ES, the offset values 1 to 1 desired by the user are stored in the calibration value storage circuit 26 (#A8), and at the same time, "End" is displayed in step #A9. The coefficient setting mode is almost the same as the offset setting mode, but the switch S
W2. 1 unit change value for 1 press of SW3 is 0.01
Therefore, the flowchart of the operation is as shown in FIG. The memorized gain coefficient is displayed in #B1, but if the user has not set it previously, it will be displayed as 1.00. From #B2 onwards, it is determined whether or not the setting SW1 has been pressed in the same way as the offset setting. If it has not been pressed, it is determined in #B3 whether SW2 has been pressed, and in #B4, SW3 is Determine whether it was pressed. In response to turning on SW 2 or SW 3,
The display is #85. #B2 to #B7 are repeated until the values are +0.01°-0.01 in #B6 and reach the values desired by the user. When the desired value is reached, press #B8.
coefficient memory”. Next, "Coefficient + Offset"
To explain the mode setting, it is a combination of Figures 4 and 5. First, the offset is displayed and set (same as in Figure 4), and when the desired value is reached, the offset value is stored in memory by SWI. , Next, the coefficients are displayed and set (same as in Fig. 5), and when finished, the coefficients are stored in the memory, and at the same time, the "coefficient + offset" mode is stored in the memory, and the setting mode ends. Operation #2 in Figure 6
to move to.

The normal operation of the chlorophyll meter having the above configuration will be described below with reference to FIG.

If you do not want to correct the calculation coefficients, turn on the power switch 9 in step #1, and the operation mode will be set to calibration mode. If you want to correct the calculation coefficients, turn on SWI~3.
By turning on the power switch 9 while turning on, the above-mentioned calculation coefficient setting mode is set and the calculation coefficient is corrected,
Move to step #2. If you look at step #2 in detail, it will look like Figure 7. #C1 selects the correction mode (“coefficient”, “offset”) stored in the calibration value storage circuit 26.
In #C2, the stored correction value is displayed to inform the measurer of the internal correction mode. For example, in the coefficient mode, the coefficient value and mode type are displayed for about 165 seconds, and then rCALJ is displayed.

If it is the offset mode, the offset value and mode type are displayed for about 1.5 seconds, and then rcALJ is displayed. "
In the "coefficient child offset" mode, fLl displays the coefficient value and mode format for about 1.5 seconds, and after displaying the offset value and mode format for about 5 seconds, rcALJ indicating that it is the calibration mode is displayed on the display section 8. indicate. These displays have the effect of making the user always aware of what operations are currently being performed on the original measurement, and are useful for data management.

After that, the display changes to rcALJ and prompts for initial calibration. In this calibration mode, the light intensity of the red light emitting diode 4 and the infrared light emitting diode 5 and the light intensity of the red light emitting diode 4 and the infrared light emitting diode 5 are adjusted without inserting the sample into the sample fixing part 12. This mode measures the temperature of the light receiving element 6, and steps #3 to #7
perform the following actions.

First, in step #3, it is determined whether the measurement switch has been pressed or not. This chlorophyll meter has a structure in which the measurement switch is automatically turned on when the rotary plate 2 is closed, and if it is determined that the measurement switch is on, the process proceeds to the next step #4. In step #4 both light emitting diodes 4.5
The amount of light and the temperature of both light emitting diodes 4 and 5 and the light receiving element 6 are measured, and the photometric value is corrected with a calibration value stored in the calibration value storage circuit 26 according to the measured temperature to obtain the amount of incident light Ior.

I oir is calculated. Next, in step #5, check whether the initial calibration is normal or not, that is, the above incident light amount for,
It is determined whether Ioir is within an appropriate range. Then, if the light emitting diodes 4 and 5 fail or deteriorate, or if mud or the like adheres to the light receiving element 6, etc., the amount of incident light may decrease.
If it is determined that the oir is outside the appropriate range, the warning circuit 27 emits an NG buzzer sound to notify that the initial calibration has failed. On the other hand, the amount of incident light f or, I oi
If it is determined that r is within the appropriate range, this incident sight is stored in the storage means (RAM) within the control calculation circuit 21, and an OK buzzer sound is emitted in step #6 to notify that the initial calibration has been completed. It will be done. When the OK buzzer sound is emitted, the display on the display section 8 becomes blank in step #7.

When the above calibration mode process is completed, the process proceeds to the measurement mode that measures the amount of light transmitted through the leaf sample.First, in step #8, it is determined whether the measurement switch is pressed or not, and the measurement switch is turned on. If it is determined that this is the case, proceed to the next step #9. In step #9, the temperature of the light emitting diode and the light receiving element is measured, the amount of light emitted from both light emitting diodes 4.5 and transmitted through the leaf is measured and temperature corrected, and the temperature corrected measurement value - (r, Iir). The amount of incident light Ior stored in the RAM of the control calculation circuit 21.

From I oir, the chlorophyll concentration Cc is determined by the above equation (1).
Next, in step #10, it is determined whether the measurement is normal, that is, whether the measured values Ir and Iir are within a proper range. If the leaf is not set correctly in the optical path and the incident light is directly received, or if the light emitting diode 4.5 or light receiving element 6 has the same problem as described above, and the amount of transmitted light is determined to be outside the appropriate range. , step #
At step #13, the measured value display becomes blank, and at step #14, an NG buzzer sound indicating that the measurement has failed is emitted, and the process returns to step #8 to wait for the next measurement. On the other hand, if it is determined that the amount of transmitted light is within the appropriate range, the chlorophyll concentration Cc is displayed on the display section 8 in step #11.
11 can be expressed in more detail as shown in FIG. That is, before displaying, it is determined in #D1 whether or not user correction has been made, and if there is no correction, it is displayed as is (
#D7゜#D8). If there is user correction, the mode is determined in #D2 or #D3, and #D4. #D5. In #D6, corrections for f thread count, offset, and coefficient offset are added, where p is the stored coefficient and q is the offset. S is a value corresponding to the density determined by measurement, and S' indicates the density after correction, if any, and the density S' after correction is displayed at #D8, and step #11 ends. .

At step #12, an OK buzzer sounds to notify that the measurement is completed, and the process returns to step #8 to wait for the next measurement.

At this point, the control calculation circuit 21 of the above embodiment executes step #4 in FIG. The temperature correction of the measured value performed in #9 will be described in detail.

The amount of light generated by the light emitting diode 4.5 has the characteristic that it decreases in proportion to the rise in temperature, and the light receiving output of the light receiving element also decreases.
have similar temperature characteristics. Therefore, for the amount of incident light in equation (1) showing the measurement principle.

I oir is expressed by the following formula.

Ioir = Iosir-fir(t-ts 1--1
211or = Iosr ・fr (t-ts)
--”・(31 However, I osr; the amount of light generated in the R region at the reference temperature Iosir; the amount of light generated in the IR region at the reference temperature t, ts; the temperature at the time of measurement; the reference temperature fr,
Temperature characteristic function (linear function) of the amount of generated light in the firHR region and the IR region The light receiving output of the light receiving element for the R region and the IR region is also expressed by the temperature characteristic functions φr (t-ts) and φjr (tts).

If the temperature at the time of calibration is tc, the incident light amounts I cr and I cir of both light emitting diodes measured in step #4 of the calibration process (c) are calculated as follows, taking into account the +21i31 formula above and the temperature correction of the light receiving output. Ier=
Iosr -fr(tc-ts)・φr(tc-t
s)・・・・・・・・・・・・(4) I+:ir = Iosir・fir(tc −t
s )・φir (t c −t s ) −
----- (51 Also, the amount of incident light I oar emitted from the re-emitting diode in step #9 of the calculation process (m),
I omir is, if the temperature at the time of measurement is tIll,
From the above equations (21, (31) and (41, +5)), it is expressed as follows.

Iomr = Iosr −fr (tm −ts
)=I crfr(tm −ts)/fr(tc−tsLφr(t e −t s)−(6
11omir=)osir-fir(tm-ts)
= Icir −f ir(tm −ts)/fir(
tc-ts)・φir (tc-ts)・・・・
・171 (61, (In formula 71, each temperature characteristic value fr
, fir.

φ', φir and the reference temperature ts are stored in the calibration value storage circuit 26 and are known, and I cr, I ctr
.

Since Ic was measured in the previous step #4 and is stored in the RAM in the control calculation circuit 21, the amount of incident light in the measurement mode (temperature; tm) is determined by these equations. moreover,
Regarding the amount of transmitted light in the measurement mode, the received light output is temperature-corrected. That is, R at the reference temperature ts and the measurement temperature tm
The amount of transmitted light in the IR region and IR region are respectively expressed as I sr and I sir
, I Ilr, I l1ir, the following equation holds true.

Imr=Isr-φr (tm-ts)I+1r
= Iir−φir(”tm −ts ) Therefore, I sr= I mr/φr (t m −t !ri −・−・・矧I sir = I air /φ
ir (tm - ts ) = 191 The amount of transmitted light in the measurement mode is corrected to the amount of transmitted light under the reference temperature using equations (8) and (91) above.

Regarding the flow of correction processing using the above measurement value correction method,
The following description will be made with reference to FIGS. 9 and 10.

The initial calibration in calibration mode step #4 in FIG.
It can be disassembled as shown in FIG. That is.

In step #21 of FIG. 9, R-LE at temperature tc
The light amount Icr of D is IR in step #22.

- The light intensity I cir of the LED and the temperature tc at that time are respectively measured in step #23, AD converted, and stored in the RAM in the control calculation circuit 21.

On the other hand, the chlorophyll amount measurement and temperature measurement in measurement mode step #9 in FIG. 6 can be broken down as shown in FIG. 10. First, in step #31, the amount of transmitted light Imr transmitted through the leaves of the R-LED is measured, in step #32 the amount of transmitted light Imi" transmitted through the leaves of the I R-LED, and in step #33, the temperature tm at that time is measured. , 0th order to be AD converted,
In step #34 and step #35, the R-LED,
The amount of light incident on the leaves of the IR-LED is corrected by +61. (This is done according to formula 7. Here, f r, f ir, φ",
φi' are the temperature characteristic function of the R-LED light amount and the temperature characteristic function of the received light output for the R region IR region light, which are known.Furthermore, in steps #36 and #37, the temperature characteristic function of the R-LED light and the IR-LED light are determined. The amount of light transmitted through the leaves I sr,
The correction of I air is performed from equation (9).
After the above correction, in step #38, 2
Find the optical density difference between wavelengths.

FIG. 11 is a diagram showing a specific example of the temperature measuring circuit,
This circuit does not use a separate temperature measurement system, but uses a light emitting diode 4 or 5 to measure the temperature. In the figure, the switching transistor Tr is driven by a control signal from the control calculation circuit 21, and emits light. Controls on/off of diode LED. The forward voltage drop of the light emitting diode LED increases the anode side potential of the light emitting diode.
It is measured by inputting it to the conversion circuit 25.

-m, the forward voltage drop of the light emitting diode and the temperature of the light emitting diode have a relationship as shown by the straight line in FIG. 6, and the voltage decreases in proportion to the rise in temperature.

The slope a and the vertical axis intercept of the straight line differ for each light emitting diode. Therefore, the values of the slopes and vertical axis intercepts of the red light emitting diode 4 and the infrared diode 5 are stored in the calibration value storage circuit 26 by two-point calibration etc., and the control calculation circuit 21 uses the stored slope a and the values of the vertical axis intercepts. The temperature T of the light emitting diode is calculated based on the input potential V on the anode side of the light emitting diode when the vertical axis is intercepted.

In this way, in the above embodiment, the temperature of the light emitting diode 4.5 is measured by measuring its forward voltage drop, so the measurement circuit is simplified and the temperature of the light emitting diode itself can be measured. There is an advantage. In addition, since the amount of light transmitted through the sample is measured only when the initial calibration has been successfully performed, preliminary adjustments can be made accurately and reliably, and subsequent unnecessary measurements due to mistakes in preliminary adjustments can be avoided. This greatly contributes to the stabilization and efficiency of measurements. Furthermore, in the above embodiment, even in the measurement mode, it is determined whether the measured light amount is within the appropriate range or not, and the result of determining whether the measured light amount is appropriate in the calibration mode and the measurement mode is notified by a buzzer sound. , measurement errors are reduced, and reliable measurements can be made.

The concentration Ce is determined from the optical density difference determined using the basic calculation flow described above using a predetermined calculation formula.

In Fig. 13, which shows an example of actually determining the calculation coefficients, the slope of the curve ■ near the wavelength λ is [approximately -0, 42
%/nm T+ = 14.06% The wavelength at which the lowest transmittance occurs is 675 nm.'' The case of the above data will be explained.

When measuring the chlorophyll concentration of a leaf that exhibits a spectral transmittance curve ■ that is different from this curve ■ and whose lowest transmittance wavelength is 685 nm, the spectral transmittance of the sample leaf Considering that the memorized curve ■ has shifted toward longer wavelengths as a whole, the rate curve ■ has a measurement wavelength of 675 nm.
The transmittance T2 at is T1 = 14.06% → T2 = I4.06 +
0.42XlO = 18.26%, and considering it in terms of optical density, Log (18,26/14.06 >'=0.11
Just subtract 3 from the measured value.

If the correction is performed using the method described above, the wavelength λs of the transmittance win will be
The correction amount for in is as shown in the table below.

Wavelength n weight 655 665 675 685
695 correction % 0.3960.154 0 -0.
113 -0.203 However, the correction amount is a numerical value that is added to the displayed value, or there is also the following correction method. This measures the amount of nitrogen per unit area and compares the amount of nitrogen with the measured value.
There is no way to correct it so that the same measured value is obtained for the same nitrogen concentration.

In this case, the nitrogen concentration in the leaves of variety ■ is X! When the measured value shows yI, the function showing the relationship between the measured value and the nitrogen concentration shown in FIG. M can be expressed as a linear equation, 3/l = aXl +b.

When the nitrogen concentration in the leaves of cultivar ■ is x2 and the measured value shows y2, the function showing the relationship between the measured value and the nitrogen concentration shown in FIG. 14 is a linear equation and can be expressed as 3/2 = CX2 + d.

Therefore, the measured value y2 of the variety ■ is the measured value y of the variety ■ with the same nitrogen concentration! To display the measured value y2
yI = [ayz −(ad bc)
]/c and perform the calculation. Therefore, when measuring leaves of a variety different from variety ■, perform such calculation and use the measured value of leaves of variety ■ with the same nitrogen concentration. If it is displayed, the same measured value can be constantly obtained for the same nitrogen concentration.

(Effects of the Invention) According to the present invention, the offset value and gain coefficient can be set freely by the user, so that the offset value and gain coefficient can be corrected depending on the sample, and the same measured value can be obtained even for different types of samples. It is now possible to display.

[Brief explanation of the drawing]

Fig. 1 is a plan view of an embodiment of the present invention, Fig. 2 is a side view of the above embodiment, Fig. 3 is a circuit configuration diagram of the above embodiment, Fig. 4 is a follow chart of the offset value setting mode, and Fig. 4 is a follow chart of the offset value setting mode. Figure 5 is a flowchart of the gain coefficient setting mode, Figure 6 is a flowchart showing the measurement operation of the above embodiment, Figure 7 is a flowchart of user correction mode display, Figure 8 is a flowchart of user correction mode, and Figure 9 is a flowchart of measurement. Figure 10 is a flowchart of the temperature correction operation for measured values, Figure 11 is a diagram of the temperature measurement circuit, Figure 12 is a temperature characteristic diagram of the light emitting diode, and Figure 13 is the spectral absorption of leaves. The rate characteristic curve diagram, FIG. 14, is a diagram showing the correlation between nitrogen concentration and chlorophyll meter display.

Claims (1)

[Claims] In an optical densitometer, the concentration of a specific substance in a sample is determined by the difference in absorbance (absorbance difference) between light in a wavelength range where absorption is large by the specific substance and light in a wavelength range where absorption is small by the substance. Optical density characterized in that it is provided with a calculation means for calculating the concentration of the specific substance using a predetermined calculation formula, and a means for correcting the calculation coefficient and offset value used in the calculation formula stored in advance. Total.