CN2259626Y - High accuracy infrared moisture measuring instrument - Google Patents

Abstract

The utility model discloses a high-precision moisture meter, which has a motor, a chopper disc, and a light window and a light filter are arranged on the chopper disc. The panchromatic light emitted by the light source passes through the lens and the rotating filter, becomes monochromatic light and enters the light guide tube, and is projected onto the measured object. Under the action of the spherical reflector, part of the monochromatic light passing through the measured object is the detection Detected by the device, and then processed by the signal processing device. The feature is that the light window and the filter on the chopping disc are fan-shaped structures. The utility model has strong signal, high signal-to-noise ratio, small size, light weight and good reliability.

Description

The infrared moisture teller of high precision

The utility model relates to moisture teller, especially relates to the infrared moisture teller of high precision.

Water has stronger absorption characteristic to the infrared light of some specific wavelength, and infrared moisture teller utilizes this specific character to come water content in the measurement of species (as material, food, paper, weaving etc.) exactly.

In above-mentioned this class was measured, the monochromatic light that needs specific wavelength usually was as light source, and this monochromatic light must utilize bandpass filter that panchromatic light is filtered usually and obtain.In order to improve the stability of surveying instrument, generally also must adopt the chopping the light device, monochromatic light is become alternation light, project measurand.

The optical window that the chopper disk of currently used infrared moisture teller is provided with and the shape of optical filter are generally circle or rectangle (to call circular configuration in the following text, rectangular configuration), the panchromatic light that light source sends, after collimated, optical filter during alternately directive rotates, light after chopping the light and optical filtering alternately projects the monochromatic light of measurand for the number bundle, after they partly see through the reflection of measurand or measurand, by detecting device is detected, again through signal processing means processes, this counts the attenuation characteristic of Shu Guang by detecting device, can determine the content of moisture content in the measurand.

The purpose of this utility model provides the infrared moisture teller of high precision that a kind of signal is strong, signal to noise ratio (S/N ratio) is high.

In order to achieve the above object, the utility model is taked following measures, and optical window that is provided with on CD and optical filter are sector structure.

The utility model has the advantages that: (1) signal is strong; (2) signal to noise ratio (S/N ratio) height; (3) significantly the influence of caused error is forbidden in minimizing because of chopper disk rotating speed or sampling timing signal; (4) volume is little, and is in light weight, good reliability.

Elaborate below in conjunction with accompanying drawing.

Fig. 1 is the infrared moisture teller structural representation of high precision;

Fig. 2 is the signal output waveform of detecting device when adopting 2 tablet filters;

Fig. 3 is chopping the light and the filtering structure synoptic diagram when adopting 2 tablet filters (circle);

Fig. 4 is chopping the light and the filtering structure synoptic diagram when adopting 2 tablet filters (fan-shaped);

The infrared moisture teller of high precision, it has motor 3, chopper disk 4, chopper disk are provided with optical window and optical filter, and the panchromatic light that light source 1 sends is behind the optical filter of lens 2 and rotation, become monochromatic light and enter light conducting cylinder 7, project measurand 11, under the effect of spherical reflector 8,9, the monochromatic light that part sees through measurand is detected by detecting device 10, handle through signal processing apparatus 12, feature is that optical window and the optical filter that chopper disk is provided with is sector structure again.Two straight lines of the optical window of sector structure and optical filter become polyline shaped or arcuation.Optical window and optical filter quantity are 2 or greater than 2.

Fig. 2 shows the signal output waveform of detecting device when adopting 2 tablet filters, u among the figure _r(t) and u _m(t) represent the responsive wavestrip signal of reference wave band signal in the two wavelength reference measurement technology and component respectively, then: $u_r\left(t\right)=u_{\mathrm{or}}\left({1-e}^{-t_r/\mathrm{\τ}}\right)----\left(1\right)$ $u_m\left(t\right)=u_{\mathrm{om}}\left({1-e}^{{-t}_m/\mathrm{\τ}}\right)----\left(2\right)$ T in the formula _rAnd t _mRepresent respectively to begin to increase from zero voltage value, to the time interval of sampling instant, t corresponding to reference wave band signal and the responsive wavestrip signal of component _R1And t _M1Represent u respectively _r(t) and u _mT when (t) arriving maximal value _rAnd t _mValue; τ is the time constant of detecting device 10.In order to reduce the influence of other factors to measuring in instrument and the measurand, adopt so-called reference technology to measure usually, promptly with ratio r=u _r(t _r)/u _m(t _m) as measured value, referring to Fig. 3 (broken circle is represented the projection of light conducting cylinder internal diameter among the figure), ideal situation has:

t _r1＝t _m1＝β/(2πf) (3)

t _r=t _mThe rotating speed of chopper disk is represented in≤β/(2 π f) (4) wherein f, effective corner when β represents measuring beam by optical window and optical filter, the corner on its expression chopping the light and filter unit when just all having entered optical window circular hole in light conducting cylinder from circular hole in the light conducting cylinder and begin to be blocked by chopper disk.Yet, during practical application, because the variation of motor speed etc. and signal sampling error constantly will cause t _r≠ t _m, t _R1≠ t _M1, if establish t _r=t _m+ Δ t, the relative error e of the ratio r that then causes thus _rFor: $e_r=\frac{u_r\left(t_r\right)/u_m\left(t_m\right)-u_r\left(t_r\right)/u_m\left(t_r\right)}{u_r\left(t_r\right)/u_m\left(t_r\right)}----\left(5\right)$ Common Δ t/ τ＜＜1, then: $e_r\≈\frac{\mathrm{\Δt}}{\mathrm{\τ}(e^{\mathrm{tm}/\mathrm{\τ}}-1)}----\left(6\right)$ As seen e _rWith Δ t, that is the variation of rotating speed f increases and proportional increase; For certain Δ t and τ, t _mBig more, e _rMore little, so the time e _rMinimum value occur in t _m=t _M1The time, its value is e _R1: $e_{r1}=\frac{\mathrm{\Δt}}{\mathrm{\τ}(e^{t_{m1}/\mathrm{\τ}}-1)}----\left(7\right)$

With the circular configuration is example, shows have as Fig. 3

β ≈ (D-d)/a (8) wherein d and D represents the diameter (with the external diameter approximately equal of optical filter) of Circularhole diameter and chopper disk optical window in the light conducting cylinder respectively, and a is the distance of optical window center to the chopper disk center.Convolution (3), (6) and (8) know that rotating speed f one regularly reduces measuring error e _R1The approach that has be to increase effective angle β, promptly increase external diameter (that is diameter of the optical filter) D of chopper disk optical window.

Fig. 3 shows when using 2 tablet filters, in the chopper disk outer diameter D ₀Under certain prerequisite, the maximum optical filter size (being less than illustrated dimensions during practical application) that can install, the maximum effective angle β that can obtain.Represented unemployed zone on the optical filter with profile line among the figure.As seen, be not utilized the large percentage of the area in zone, and the increase with D increases, certainly will increase the weight of the chopping the light and the filter unit of high-speed rotation like this, that is increased the load of micromachine, this means the increase of chopping the light and filter unit volume and the reduction of instrument reliability, obviously this is harmful to.

In addition, in order to improve measuring accuracy, must improve the signal to noise ratio (S/N ratio) of detecting device, detecting device (as the PbS detecting device) is operated under the lower temperature, but increased the timeconstant of detecting device like this, so, more need bigger effective angle β for increasing detector output signal amplitude and the influence that reduces the chopper disk rotation speed change, obviously in this case, the defective of above-mentioned circle and rectangular configuration is more outstanding.

The chopping the light that the utility model proposed and the basic thought of filtering structure are: the sector structure (being designated hereinafter simply as sector structure) of the shaped design Cheng Yuqi of optical window on the chopper disk and optical filter effectively being utilized regional basically identical.The sketch of chopper disk and filter set is seen Fig. 4 (wherein broken circle is the projection of light conducting cylinder internal diameter) when using 2 tablet filters, in this structure, almost removed in circular and the rectangular configuration and be not utilized the zone, thereby, compare with rectangular configuration with tradition is circular, at chopper disk overall dimensions and chopper disk rotating speed f etc. regularly, this sector structure can guarantee under the less prerequisite of optical filter weight, increased effective angle β to greatest extent, that is reduced to greatest extent because of caused errors such as chopper disk rotating speed or sampling instant errors, increased the amplitude of signal shown in Figure 2 to greatest extent, help improving the signal to noise ratio (S/N ratio) and the Instrument measuring precision of measurement, help improving the reliability of instrument.

Table 1 has been listed (f=50 ± 2Hz, τ=0.5ms, D under the set condition ₀=120mm, d=10mm), under the equiponderant prerequisite of the optical filter of circular configuration and sector structure, the effective angle and the maximum ratio error e of chopping the light and filter unit when adopting these two kinds of structures respectively _R1Value.

Table 1

Sequence number	β(°)		|e r1|
					Fan-shaped	Circular	Fan-shaped	Circular
	1	20	17.6	1.1％					1.9％
2					30	22.3	0.49％	0.9％
	3	40	26.6	0.21％					0.65％
4					50	30.6	0.09％	0.47％
	5	60	34	0.03％					0.35％

These results are representative, as seen from Table 1, the ratio measuring error | e _R1| along with effective angle β increases and reduces rapidly, optical filter for equal area (being weight), the effective angle β of sector structure is bigger than circular configuration (in fact also than rectangular configuration), and when the area of optical filter increased, the speed that the effective angle of sector structure increases was circular and rectangular configuration is much bigger.In other words, equate or the chopper disk external diameter equates under the prerequisite at optical filter area (being weight), use sector structure little than the ratio error of traditional structure, especially as β greatly the time, this species diversity is bigger.As shown in table 1, when the β of sector structure was 60 °, its ratio error was less than 1/10 of equal areas (being weight) circular configuration.

Be understood that, when the timeconstantτ of detector is larger, for obtaining larger measuring-signal amplitude (seeing Fig. 2) and less ratio measure error, larger effective angle β must be arranged, use above-mentioned sector structure to also have volume little than traditional structure, lightweight, high reliability.

Claims (3)

1. infrared moisture teller of high precision, it has motor [3], chopper disk [4], chopper disk is provided with optical window and optical filter, the panchromatic light that light source [1] sends is behind the optical filter of lens [2] and rotation, become monochromatic light and enter light conducting cylinder [7], project measurand [11], under the effect of spherical reflector [8], [9], the monochromatic light that part sees through measurand is detected by detecting device [10], handle through signal processing apparatus [12] again, it is characterized in that optical window and optical filter that said chopper disk is provided with are sector structure.

2. the infrared moisture teller of a kind of high precision according to claim 1 is characterized in that the optical window of said sector structure and two straight lines of optical filter become polyline shaped or arcuation.

3. the infrared moisture teller of a kind of high precision according to claim 1 and 2 is characterized in that said optical window and optical filter quantity are 2 or greater than 2.

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