WO2001092839A2

WO2001092839A2 - Apparatus for detecting and measuring intensity of ultraviolet radiation

Info

Publication number: WO2001092839A2
Application number: PCT/US2001/015994
Authority: WO
Inventors: Michael J. Madigan
Original assignee: Calgon Carbon Corporation
Priority date: 2000-05-31
Filing date: 2001-05-17
Publication date: 2001-12-06
Also published as: TW487799B; AU2001274846A1; WO2001092839A3

Abstract

An apparatus is provided for detecting UV radiation and measuring the intensity of such radiation. The apparatus includes a semiconducting photosensitive device capable of detecting and responding to UV radiation wavelengths in the range from about 180 nm to about 360 nm. In particular, the photosensitive device is a photodiode based on silicon carbide semiconducting material having a peak response in the wavelength range of about 240 nm to about 290 nm. The UV sensor exhibits long-term stability, linear output, and low variation of output with respect to environmental temperature fluctuation.

Description

TITLE

APPARATUS FOR DETECTING AND MEASURING INTENSITY OF

ULTRAVIOLET RADIATION

FIELD OF THE INVENTION

The present invention relates to an apparatus for detecting ultraviolet ("UV") radiation and measuring the intensity of UV radiation transmitted through a fluid. In particular, this invention relates to an apparatus for measuring the intensity of UV radiation emitted from a UV radiation source and transmitted through water.

BACKGROUND OF THE INVENTION

Systems and apparatuses for disinfection of water with UV radiation have been developed in response to increased awareness of possible presence of harmful microorganisms in water sources. It has been known that the deoxyribonucleic acid ("DNA") of microorganisms submitted to UV radiation undergoes modifications which can prevent their replication. The bombardment of the microorganisms by UV renders them substantially inactivated and incapable of infecting the host. As used herein "UV radiation" means radiation having a wavelengths from about 180 nm to about 400 nm. The statistical proportion of microorganisms of a given type inactivated by UV radiation within a given population is directly related to the UV dose (the product of the irradiance.of UV radiation and time of exposure) received by that population. UV doses are typically measured in mW. sec/cm² (or, identically, mJ/cm²). The irradiance (measured in mW/cm²) is the total radiant power of all radiation wavelengths on a unit cross-sectional area perpendicular to the direction of propagation of radiation wave.

In order to ensure a high degree of inactivation of microorganisms and, thus, a high degree of disinfection, it is necessary that water receives a certain minimum UN dose for a given treatment application. Therefore, it is essential that the UN sources used for irradiation be monitored to ensure a continuous and efficient operation of the treatment system. Certain wavelengths, in particular 254 nm, have a higher germicidal efficiency than others. There are three main types of UV sources commercially available at present: low-, medium-, and high-pressure lamps. Low-pressure mercury-vapor UV ("LP-UV") lamps emit nearly monochromatic radiation of 254 nm, which is the optimal wavelength for germicidal efficiency. The mercury vapor pressure in LP-UV lamps is in the range of 10^" to several millimeters of mercury when the lamps are energized. LP-UV lamps commercially available provide a power in the range of 50-200 W. The demarcation line between medium- and high-pressure mercury-vapor lamps is imprecise. Medium-pressure mercury- vapor UV ("MP-UV") lamps as used herein refer to MP-UV lamps having mercury vapor pressure in the range from about 1 to about 10 atmospheres when the lamps are energized. The wavelengths of radiation emitted by MP-UV lamps are predominantly shorter than about 366 nm. High-pressure mercury- vapor ("HP-UV") lamps as used herein refers to HP- UV lamps having mercury vapor pressure greater than about 10 atmospheres during operation. When the mercury vapor pressure rises to several hundred atmospheres when the lamp is energized, the emission spectrum is essentially a continuum and comprises a large part of the visible spectral region (i.e., wavelengths from about 400 nm to about 700 nm) with intense radiation at wavelengths of 436 nm and 546 nm. See, e.g, A.M. Braun et al., Photochemical Technology, pp.109-115 (1991). Because the dominant modes (i.e., the peaks) of emission spectra of MP-UV and HP-UV lamps are shifted away from 254 nm to longer wavelengths, these lamps have lower germicidal efficiency. However, they can have much higher unit power. Lamps having power up to 100 kW are available. On balancing between the unit power and the emission wavelength, MP-UV lamps are often chosen for the disinfection treatment of water.

It is known that UV radiation may be monitored by deploying passive sensors near the operating lamps. Examples of these passive sensors are photodiodes, photoresistors, and phototubes (or photocells) that can respond to the bombardment by the particular radiation of interest by producing a reproducible and measurable electrical signal. Typically, this signal is exhibited as an electrical voltage or a current. Ideally, the sensor signal should exhibit low drift over time; low sensitivity to temperature; rapid return to base line upon removal of the radiation source; and, most importantly, high sensitivity in the range of wavelengths of interest. Several UV sensors are known. For example, U.S. Patent 5,497,004 discloses a UV sensor that includes a silicon oxide dispersive element disposed between the photodetector and the UV radiation source to provide long-term protection to the photodetector against intense radiation damage. The dispersive element allows only about 10 percent of the incident radiation to reach the photodetector. Because about ninety percent of the incident radiation is dispersed, an accurate measurement of the true radiation dose may be compromised.

U.S. Patent 5,514,871 discloses an optical radiation sensor device that iⁿcludes attenuating apertures disposed between the radiation source and the sensor. A filter means is also provided to remove radiation in the visible region. The attenuating apertures limit the amount of radiation reaching the sensor to slow the process of irreversible degradation of the sensor. An accurate measurement of the true radiation dose may also be compromised in this case because of the need for attenuation.

Therefore, it is an object of the present invention to provide a UV sensing and measuring device that overcomes disadvantages of prior-art UV sensing devices. It is a further object of the present invention to provide a UV sensing and measuring device that has improved stability with time and temperature, improved specificity with respect to the UV wavelengths that are more germicidally effective, and improved accuracy of measurement of UV radiant power for use in water disinfection applications. These and other advantages of the present invention will become apparent upon a perusal of the instant disclosure. SUMMARY OF THE INVENTION

The present invention provides a device for detecting UV radiation and measuring the radiant power of such radiation emitted from a UV radiation source. The UV sensor of the present invention comprises a housing having a first end that allows UV radiation to enter the housing and a second end through which electrical connections may be made; a quartz glass window disposed at the first end of the housing and in the line of radiation transmission; a sensing means capable of detecting and responding to UV radiation, which sensing means is disposed inside the housing and oriented to receive the UV radiation; and an electrical circuit for converting, conditioning, and amplifying the signal generated by the sensing means. The first end of the housing and the quartz window allow the UV radiation sensing means to receive UV radiation substantially unimpededly. Optionally, the UV sensor of the present invention may also include electrical connections and wiring for transmitting the conditioned and amplified signal from the electrical circuit to other devices located remotely from the UV sensor.

Various sensing means that are capable of detecting and responding to UV radiation may be used in a UV sensor of the present invention and are chosen according to the particular range of wavelengths of interest. Typically, sensing means are based on the capability of semicon^n^ting materials to generate or of conducting materials to change an electrical current upon being bombarded by photons of radiation. For example, the sensing means may be a photoconductive cell, a photoemissive device, or a photosensitive device.

When a semiconducting material is bombarded by photons with energy greater than the band gap energy of the semiconducting material, electrons are raised to the conduction band and are free to conduct current. Non-limiting examples of materials capable of electronically responding to the bombardment of photons are diamond, cadmium sulfide, silicon, gallium, arsenic, germanium, indium and selected compounds thereof. A preferred

UV sensing means for the present invention is a photodiode using silicon carbide (SiC) semiconducting material which exhibits the maximum response to UV radiation having wavelengths in the range from about 240 nm to about 320 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure la is a perspective drawing of an assembled UV sensor of the present invention. Figure lb shows a perspective exploded view of the UV sensor of the present invention.

Figure 2 shows a sectional view of an assembled UV sensor of the present invention.

Figure 3 is a perspective drawing of a water treatment chamber using UV radiation for the inactivation of microorganisms. Figure 4 is the cross-sectional view of the water treatment chamber showing the location of a UV sensor of the present invention in relation to a UV radiation source.

Figure 5 shows circuit diagram for the amplification and conditioning of the electrical output from the UV sensing element.

Figures 6 shows the stability of a UV sensor of the present invention in a long-term use.

Figure 7 shows the linearity of the output signal of a UV sensor of the present invention with respect to the irradiance of a UV lamp.

Figure 8 shows the low variation of the output signal of a UV sensor of the present invention with respect to water temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure la shows a perspective view of the UV sensor of the present invention. UV sensor 30 comprises a sensor housing 32, preferably cylindrical, whjch has two opposed ends. First end 34 through which UV radiation passes substantially unimpededly is sealed by a cover means 40, such as a retaining nut, ring, or gland. When cover means 40 is made of a metal, an opening substantially equal to the inside diameter of the sensor housing is formed into the cover means to allow UV radiation to pass through. Cover means 40 also may be made of a solid piece of quartz glass. Second end 36 of the sensor housing 32 receives a fitting 52 for electrical cable 50 which is connected to an electrical circuit which is disposed inside the sensor housing 32 and used to condition and amplify the signal from the UV sensing means. A shoulder 35 is formed around the sensor housing 32 and at a distance from the first end 34 so that, in combination with gasket 33, the shoulder 35 ensures a tight fit of the UV sensor 30 inside fitting 31. ^•'

Figure lb is an exploded perspective view of the UV sensor of the present invention. The relative positions of the various components of the UV sensor are substantially as shown in Figure 2. Similar components in Figures lb and 2 are represented by the same numeral. Sensor housing 32 may be made of a non-corrodible metal such as stainless steel. In a preferred embodiment sensor housing 32 is a hollow cylinder. A support gasket 38 is formed inside sensor housing 32 at a short distance from the first end 34. A first gasket 42 is disposed tightly inside the .sensor housing and against support gasket 38. Preferably support gasket 38 comprises a ring and first gasket 42 is an O-ring. A UV transmissive quartz window 44 is disposed against first gasket 42 and, preferably, has the form of two concentric discs of different diameter. The diameter of the larger disc is substantially equal to the inner diameter of sensor housing 32. The diameter of the smaller disc is substantially equal to the opening in cover means 40 so that it traverses cover means 40. This quartz window design significantly eliminates the occurrence of an air bubble in the opening of the cover means experienced with use of a flat quartz window. Because the transmittance of UV radiation is different in air than in water such an unpredictable formation of air bubble would render the measurement of UV power inaccurate.

A second gasket 46 fits around the smaller disc of the quartz window 44. Cover means 40 and support ring 38 together retain the quartz window 44 in place. UV sensing means 56 is disposed on and electrically connected to an electrical circuit on circuit board

54. The electrical circuit is capable of amplifying and conditioning very low levels of electrical signals, such as those generated by the UV sensing means. Such an electrical circuit is well known. Electrical cable 50 is connected to circuit board 54 through fitting 52 which securely fastens the cable to the sensor housing 32. A plastic cylindrical spacer 58 fits over the UV sensing means 56 to ensure a stability of the UV sensing means 56. The spacer 58 has a sufficient length so to rest against the support gasket 38 when the UV sensor is completely assembled.

In another embodiment, the UV sensor of the present invention may be used in conjunction with a water treatment system such as shown in Figure 3. A plurality of UV sensors 30 are disposed in a water treatment system 10 which comprises a water treatment chamber 11 having a water inlet 12 and a water outlet 13. Met 12 and outlet 13 comprise, for example, standard pipe flanges 14 and 15 for connecting to a water handling system, such as that of a water treatment plant. A plurality of UV lamps, each disposed inside a protective quartz sleeve 21, is arranged perpendicularly to the direction of water flow inside the treatment chamber 11 through fittings 23. A plurality of UV sensors 30 are disposed on the water treatment chamber through fittings 31 formed into the wall of the treatment chamber such that one UV sensor is associated with one lamp to detect and measure the radiant power of UV radiation emitted from the lamp. Each UV sensor 30 is oriented substantially perpendicularly to a UV lamp. When a sensor detects a drop in radiant power of the UV lamp below a predetermined level, the UV lamp is replaced to ensure that the water always receives a minimum dose of UV radiation for effective disinfection.

Figure 4 shows the cross-sectional view of the water treatment chamber 11. UV lamp 20 is installed diametrically across the cross section of the treatment chamber and is protected by a quartz sleeve 21. A movable quartz cleaner 22 is disposed around the quartz sleeve 21 for periodically removing insoluble deposit on the quartz sleeve to ensure that substantially full radiant power of the UV lamp is received by the water. The movement of the quartz cleaner 22 may be effected by pressure of a compressed gas or a hydraulic fluid supplied through a cylinder 24. A UV sensor 30 is disposed through a fitting 31 formed into the wall of the treatment chamber such that the UV sensor directly faces and receives UV radiation from the UV lamp 20. The electrical signal generated irom UV sensor 30 is transmitted through electrical cable 50 to remote measuring and process controlling devices (not shown). A plurality of baffles 26 is disposed against the interior surface of the treatment chamber to increase the mixing of water for a more effective treatment.

Figure 5 shows a circuit diagram for the amplification and conditioning of the electrical output from UV sensing means 56. IC1 is an amplifier well known in the electronic art and is available from Boston Electronics Corporation, Brookline,

Massachusetts. IC2 is a voltage-to-current (4-20 mA, model number AD694JN) converter and is available from Analog Devices, Norwood, Massachusetts. IC3 is a voltage regulator (model number LM78_^15AC) and is available from National Semiconductor, Santa Clara, California. Preferably, the present invention UV sensing means 56 is a photodiode based on SiC semiconducting material. The peak response of SiC in terms of current generated per unit UV radiation power received is in the wavelength range from about 250 nm to about 290 nm, and the response to UV radiation is very low for wavelengths below about 200 nm and above about 380 nm. See; e.g., D.M. Brown et al., "Silicon Carbide UV Photodiode," IEEE Transactions on Electron Devices, Vol. 40, No. 2, pp. 325-32 (February 1993). A SiC- . ..^'. based UV photodiode suitable for the UV sensor of the present invention is available from Boston Electronics, Brookline, Massachusetts. Moreover, an optical filter may be used in conjunction with a SiC photodiode to reduce the response of the photodiode to UV wavelengths longer than 290 nm, further enhancing the sensitivity for the measurement of UV radiant power around the germicidal wavelength of about 260 nm.

In another embodiment of the UV sensor of the present invention, the cover means may be manufactured from quartz and serves also as the window for the photodiode. In this case, the cover means 40 is attached to sensor housing 32 and substantially leveled with sensor housing end 34 so that formation of air bubbles is substantially prevented. The UV sensor of the present invention has many advantages over prior art UV detectors in the application of water disinfection. The UV sensor of the present invention has a high sensitivity to UV radiation having wavelengths in the range from about 240 nm to about 320 nm which includes the most germicidal effective UV wavelength of 254 nm. It has been known that the DNA of microorganisms submitted to UV radiation undergoes modifications which prevent their replication. It is believed that upon absorption of UV quanta, two adjacent pyrimidine nucleobases of the DNA strand can dimerize to form a thymine dimer. Such a lesion can prevent the replication of the DNA strand and, thus, the replication of the cell. Therefore, the cell can no longer propagate to infect the host. The absorption of UV by DNA exhibits two peaks at wavelengths of about 200 nm and about 260 nm. See; e.g., C. von Sonntag and H-P. Schuchmann, J. Water Supply Res. and Techn.- -Aqua, "UV Disinfection of Drinking Water and By-Product Formation— Some Basic Considerations," Vol. 41, No. 2, pp. 67-74 (1992).

LP-UV and MP-UV mercury vapor lamps are most appropriate for use in the disinfection of water because they emit UV radiation predominantly near or in a narrow range around 260 nm. The UV sensor of the present invention has high response or sensitivity to UV radiation in the range wavelengths from about 240 nm to about 320 nm and, thus, provides a more accurate monitoring of the performance of these lamps. Furthermore, an optical filter may be provided in conjunction with the sensor of the present invention to filter UV radiation wavelengths from about 290 nm to about 400 nm to focus the detection and measurement near the germicidal wavelength of about 260 nm. The UV sensor of the present invention exhibits many other advantages. Figure 6 shows the stability of the sensor, as exhibited by the sensor electrical output per unit UV irradiance power, after nearly 1500 hours of testing in a realistic water treatment experiment using MP-UV lamps without any indication of radiation damage even when the sensor received the full power from a lamp without the need for attenuation. The output signal of the UV sensor of the present invention is substantially linear over a wide range of UV irradiance as is shown in Figure 7. This linearity provides a faithful measurement of the actual UV radiation dose that the water receives. The output signal of the UV sensor of the present invention also exhibits low variation with respect to the temperature with which it is in contact, as is shown in Figure 8. This characteristic is advantageous and important because a UV sensor, such as that of the present invention used in a water treatment plant, is exposed to a wide range of environmental temperature. While the foregoing has described the preferred embodiments and modes of operations of the present invention, it should be appreciated that numerous variations, changes, and equivalents may be made to these embodiments and modes of operation without departing from the scope of the present invention as defined in the following claims.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for detecting and measuring UV radiation and radiant power from about 180 nm to about 400 nm comprising:

(a) a housing having first and second spaced apart ends said first end to receive radiation from an UV radiation source;

(b) a quartz window sealingly disposed in said first end, said quartz window being capable of transmitting UV radiation at least from 180 nm to 400 nm.;

(c) a UV radiation sensing means disposed between said first and second ends in said housing to receive any UV radiation transmitted through said first end and said quartz window, said UV sensing means being capable of detecting any said UV radiation and generating a measurable related electrical signal; and

(d) an electrical circuit to amplify and condition said electrical signal to generate a detectable amplified and conditioned electrical signal.

2. An apparatus for detecting and measuring UV radiation as recited in claim 1 wherein said UV radiation passes substantially unimpededly through said first end and said quartz window.

3. An apparatus for detecting and measuring UV radiation as recited in claim 2 further comprising electrical connecting and transmitting means to conduct said detectable amplified and conditioned electrical signal to devices located away from said UV- detecting and measuring apparatus.

4. An apparatus for detecting and measuring UV radiation as recited in claim 2 wherein said UV radiation sensing means is selected from the group consisting of photoconductive cells, photoemissive devices, photo transistors, and photodiodes.

5. An apparatus for detecting and measuring UV radiation as recited in claim 4 wherein said UV radiation sensing means a silicon carbide photodiode.

6. An apparatus for detecting and measuring UV radiation as recited in claim 4 wherein said UV radiation sensing means responds to UV radiation having wavelengths in a range of about 240 nm to about 320 nm.

7. A method for monitoring a performance of a UV emitter comprising:

(a) detecting UV radiation with a new apparatus claimed in claim 1 positioned proximately to said UV emitter;

(b) recording an amplified and conditioned electrical signal from said UV radiation sensing means; and

(c) inspecting said amplified and conditioned electrical signal over a period of " operation of said UV emitter.

8. A method for monitoring a performance of a UV emitter as recited in claim 7 further comprising the step of (d) replacing said UV emitter when said electrical signal shows a deterioration of the performance of said UV emitter below a predetermined level.

9. A method for monitoring a performance of a UV emitter as recited in claim 8 wherein said UV emitter is selected from the group consisting of low-pressure mercury-vapor UV lamps and medium-pressure mercury-vapor UV lamps.

10. A method for monitoring a performance of a UV emitter as recited in claim 9 wherein said UV emitter is disposed in a flow of water to effect a disinfection of said water.