JPH0266426A - Measuring instrument for scattered light - Google Patents

Abstract

PURPOSE:To remove both the influences of dark current and sensitivity change by arranging a dark current measuring photosensor whose photodetecting faces are shielded near photosensors for measuring the intensity of scattered light and correcting the outputs of partial photosensors by the output ratios of amplifiers with sensitivity compensation and amplifiers without sensitivity compensation. CONSTITUTION:The dark current measuring photosensors Pb1, Pb2 whose photodetecting faces are shielded are arranged near plural scattered light measuring photosensors P1 to Pn, Ps arranged corresponding to scattered angle of scattered light and the outputs of photosensors Pb1, Pb2 are corrected by mutual photodetecting area ratios and the corrected values are subtracted from the outputs of the photosensors P1 to Pn, Ps. For instance, the output of the photosensor Pn is inputted to the amplifier 10 with sensitivity compensation and the amplifier 9 without sensitivity compensation, the ratio of the outputs is calculated and the outputs of the other photosensors P1, to Pn-1 are corrected by the output ratio. Consequently, the influences of dark current due to the scattered light measuring photosensors and sensitivity change can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a device for measuring scattered light generated by, for example, irradiating light onto particles in a dispersed state. This invention relates to a scattered light measuring device that can be applied to distribution measuring devices and the like.

<Prior art> In a laser beam diffraction/scattering type particle size distribution measuring device, a laser beam is irradiated onto sample particles in a dispersed state in a medium, and the intensity distribution of the light diffracted or scattered by the sample particles is measured. By doing so, the particle size distribution of the sample particles is calculated based on Franhofer diffraction or Mie scattering theory.

In this type of measurement device, a suspension of sample particles dispersed in a medium is usually placed in a measurement cell and irradiated with light. A lens for condensing light is provided, and a so-called ring detector is provided at the focal point of the lens, in which a plurality of ring-shaped photosensors with different radii are arranged concentrically. ) is the intensity distribution (relationship between scattering angle and intensity).

By the way, in this type of particle size distribution measuring device, only a pure medium is placed in the measurement cell, and the intensity of the scattered light when the medium is irradiated with a laser beam is used as a blank value (base value), and the intensity of the scattered light is used as a blank value (base value). This blank value is subtracted from the scattered light intensity when the laser beam is irradiated to obtain the true scattered light intensity, so if there is no temperature difference between the blank value measurement and the scattered light measurement using the sample suspension, the above-mentioned The dark current value of the photosensor is erased by subtraction. In addition, since ring detectors are generally manufactured by forming a large number of ring-shaped photosensors on a common wafer in the same process, the sensitivity characteristics of each sensor on this ring detector are considered to be almost the same, and the relative Due to the principle of the method of determining particle size distribution from light intensity, changes in the sensitivity of each photosensor do not have much influence on the particle size distribution measurement results.

<Problems to be Solved by the Invention> However, when using the device in a place with large temperature changes, the effect of dark current will occur unless the blank value is measured frequently. , when installing a photosensor for measuring scattered light at a large angle such as 90° to the side of the measurement cell, if there is a difference in temperature fluctuation between the two, the difference in dark current fluctuation due to this and the relative sensitivity Changes directly affect the particle size distribution measurement results, resulting in measurement errors. In particular, since the sensor for measuring large-angle scattered light is installed on the side immediately adjacent to the measurement cell, it is susceptible to the influence of temperature when measuring a suspension that has a temperature difference from room temperature.

Scattered light is weak, and when a semiconductor photosensor is used, the influence of dark current is large.Also, this dark current changes exponentially with temperature, so it is difficult to use only the electrical circuit of the signal processing system. Correction is difficult, and since there are a large number of photosensors to correct sensitivity changes, it would be expensive to add a sensitivity compensation function to each amplifier.

The present invention has been made in view of these points, and an object of the present invention is to provide a scattered light measuring device that can eliminate the effects of dark current and sensitivity changes in a photosensor for measuring scattered light by adding only a few parts. It is said that

<Means for Solving the Problems> A configuration for achieving the above object will be described with reference to FIGS. 1 and 2 corresponding to the embodiment. A dark current measurement photosensor PbI (and Pb Photo sensor P1 for light measurement
From the outputs of ~P, , (Ps), the outputs of the dark current measurement photosensors Pb+(Pb□) are corrected and subtracted by the mutual light-receiving area ratio, and among the scattered light measurement photosensors, the outputs of the same wafer are subtracted. Photo sensor groups P1 to P formed above
Regarding 7, some photosensors (for example, P
fi) is input to each of the amplifiers 10 and 9 with sensitivity compensation and without sensitivity compensation, respectively, and amplifies both of them.
9. Calculate the output ratio of 1O, and calculate the output ratio of the other photosensors P1 to P.
The output of 7-1 is characterized by being input to amplifiers 9 . . . 9 without sensitivity compensation, and the amplifier outputs are corrected by the above output ratio.

Effects> The output i of the photosensors P1 to P, (Ps) is considered to be: i=incident light intensity×coefficient×(1+temperature coefficient×Δt)+dark current, where Δt is the temperature difference from the reference temperature.

Here, although the magnitude of the dark current changes exponentially with temperature change as described above, it is proportional to the light-receiving area for the same type of photosensor at the same Δt.

A dark current measurement photosensor Pb+ (or Pb□) whose light-receiving surface is shielded is provided near the photosensors P1 to P, (or Ps), and the photosensors P, ~p-(ps
), from the output 11~i n(t s), P(pb□)
By subtracting the output ib+(ib□) after correcting it by their area ratio, the influence of dark current is canceled even if there is a temperature change.

Regarding sensitivity changes, it is considered that the photosensor groups P1 to P, formed on the same wafer have the same characteristics and are also approximately the same in temperature, so for example, the output of photosensors P and 1 is considered to be the same. is input to both the amplifier 10 with sensitivity compensation and the amplifier 9 without sensitivity compensation to calculate the output ratio, and calculate the output ratio of the other photosensors P I ” P n
By correcting the -1 output using this output ratio, the sensitivity can be equivalently corrected.

<Embodiment> FIG. 1 is a plan view showing the configuration of an embodiment of the present invention, and FIG. 2 is a front view of the light-receiving surface of the ring detector 5. This example shows an example in which the present invention is applied to a laser beam diffraction/scattering type particle size distribution measuring apparatus.

The sample particles W are flowed into the measurement cell 1 while being uniformly dispersed in the medium.

An irradiation optical system consisting of a laser light source 2 and a beam expander 3 is disposed behind the measurement cell 1, and is capable of irradiating sample particles W in the measurement cell 1 with a parallel laser beam having a predetermined cross section. can.

A Fourier transform lens 4 is disposed on the optical axis of the irradiation light in front of the measurement cell 1 for condensing the light scattered by the sample particles W, and a ring detector 5 is disposed at its focal position. ing.

As shown in FIG. 2, the ring detector 5 includes n ring-shaped semiconductor photosensors P+ each having a different radius around the optical axis of the irradiated light on a common wafer 51.
, Pz . In addition, in this ring detector 8, a photosensor Pbl for dark current measurement is formed on the same wafer 51, separately from P1 to P, l. Each photo sensor P for dark current measurement is mounted on the wafer 51.

~P7 is formed by the same process, and its light receiving surface is shielded from external light by a shielding plate 6.

On the side of the measurement cell 1, a photosensor P for measuring side (90") scattered light is arranged, and in the immediate vicinity thereof, there is a light-receiving surface having the same area as this photosensor P. A dark current measuring photosensor Pb□, which is formed by covering the light-receiving surface of an identical photosensor with a shielding plate, is provided.

The outputs of each of the photosensors P1 to P, l on the ring detector 5, the dark current measurement photosensor Pbl, the side scattered light measurement photosensor P, and the nearest dark current measurement photosensor Pb2 are as follows. Preamplifier 8...8
has been entered. Regarding the photosensors P, -P, and Pbl on the ring detector 5, only the output 17 of the photosensor P7 is sent via the preamplifier 8 to both the amplifier 10 with sensitivity compensation and the amplifier 9 without sensitivity compensation. The outputs of the other photosensors P1 to Py+-1 and Py to il to 1+1-1 and ib+ are input to amplifiers 9 and 9 without sensitivity compensation via preamplifiers 8...8, respectively. ing. Also, a photosensor P for measuring side scattered light.

and the outputs i3 and i of the photosensor PbZ for dark current measurement
For b□, after passing through the preamplifier 8.8, respectively,
A signal obtained by subtracting ibz from the output i3 is input to the amplifier 10 with sensitivity compensation.

Then, the outputs of all the amplifiers 9...9 and 10.10 are sequentially sent to the A-D converter 12 via the multiplexer 11.
After being digitized by the computer 13, it is configured to be imported into the computer 13.

In the computer 13, each amplifier 9...9 and 10
．． After taking in the digital conversion data from 10 and performing the calculations shown below, the corresponding photosensors P,
- Measurement of intensity of scattered light by P and P - used as data to calculate particle size distribution.

That is, the computer 13 has the areas Δ1 to A7 and A bl of each light receiving surface of the photosensors p, -p on the ring detector 5 and the photosensor Pbl for dark current measurement.
is input in advance, and each photosensor P, -P
, through the amplifiers 9 without sensitivity compensation...
Let D'r+ be the data taken through 0, and ab+ be the data taken from the dark current measurement photosensor Pbl through the amplifier 9. First, calculate the following. Next, after calculating D,=K − for j=1 to n−1
d, ...(4) is calculated.

Then, D1 to Dll are employed as light intensity measurement data by each of the photosensors P1 to P on the ring detector S.

In addition, regarding the data D obtained through the amplifier 10 with sensitivity compensation by subtracting the output of the photosensor Pb2 for measuring dark current from the output of the photosensor P for side scattered light measurement, this value is left unchanged. Adopted as side scattered light measurement data.

According to the embodiment of the present invention described above, the photosensor PL-P7 on the ring detector 5 and the photosensor P for dark current measurement are formed on the same wafer 51 by the same process. , each exhibits almost the same characteristics as each other, and their positions are close to each other, so it can be assumed that the temperature of each changes almost the same even when the ambient temperature changes. From this, the photosensor PI- It may be considered that the dark currents of P, l, and Pbl are proportional to the areas of their respective light-receiving surfaces. Therefore, by equations (1) and (21, the influence of dark current is removed from each data, and by equations (31 and (4), the data from the photosensor P l"" P n-1 is equivalently Furthermore, the output of the side scattered light measurement photosensor P is also compensated for after the output of the dark current measurement photosensor Pb2, which is the same photosensor placed immediately next to it, is eliminated. Amplifier 1 with sensitivity compensation
Since the amplification is performed at 0, the effects of dark current and sensitivity changes are completely removed.

Note that the amplifier 10 with sensitivity compensation is an amplifier obtained using a generally known resistor having a high temperature coefficient.

Further, in the above-described embodiments of the present invention, the output of each photosensor is inputted to the amplifier via the preamplifier, but it goes without saying that the output of the photosensor may be inputted to the current amplifier.

<Effects of the Invention> As described above, according to the present invention, one or more photosensors for dark current measurement are provided in the vicinity of the photosensor for measuring scattered light, and one amplifier with sensitivity compensation is provided.
By simply adding one or two pieces, it is possible to eliminate the effects of both dark current and sensitivity changes. By applying it to particle size distribution measuring equipment, it is possible to eliminate blank values even when measuring in places with rapid temperature changes. Accurate scattered light intensity can be obtained without repeated measurements, and measurements with few errors can be made even with samples at high or low temperatures. Furthermore, for the same reason, the reliability is also improved in a combined measurement using a ring detector and one or more other photosensors such as a photosensor for measuring side scattered light.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing the configuration of an embodiment of the present invention, and Fig. 2 is a plan view showing the structure of the lid 2... 5... 6.7... 8... 9... 10... PIS-Pfl, Ps... pbt.・ It is a front view of the “pbz” ring detector 5. ・ Measurement cell ・ Laser light source ・ Ring detector ・ Shielding plate ・ Preamplifier ・ Amplifier without sensitivity compensation ・ Amplifier with sensitivity compensation ・ Photo sensor ・ Photo sensor for dark current measurement

Claims (1)

[Claims] In a device for measuring scattered light generated by irradiating an object such as a particle with light, a light receiving surface is shielded near a plurality of photosensors for measuring the intensity of scattered light arranged corresponding to each scattering angle. A photosensor for measuring dark current is provided, and the output of the photosensor for measuring dark current is corrected and subtracted from the output of each photosensor for measuring scattered light intensity, and the output of each of the photosensors for measuring the intensity of scattered light is corrected and subtracted from the output of each of the photosensors for measuring scattered light intensity. Among the photosensors for measuring the intensity of scattered light, for a group of photosensors formed on the same wafer, the outputs of some of the photosensors are input to each amplifier with sensitivity compensation and without sensitivity compensation. Calculate the output ratio of the amplifier,
A scattered light measuring device characterized in that the outputs of the other photosensors are input to an amplifier without sensitivity compensation, and the output of the amplifier is corrected by the output ratio.