Hamamatsu UVTRON Istruzioni operative

TECHNICAL INFORMATION

How to Use UVTRON®

FEATURES

Capable of detecting very weak ultraviolet light (down to 1 pW)

Insensitive to visible and infrared light (solar blind characteristics)

High reliability and long life (over 10,000 hours of continual discharge operation)

High-speed response (less than a few milliseconds)

Low current operation

Miniature size and lightweight

APPLICATIONS

Combustion monitors for gas/oil burner

Fire alarms

Arson surveillance sensors

Flame detectors for gas/oil lighters and matches

Detection of ultraviolet light leakage

Detection of discharge phenomenon

Figure 1 shows typical spectral radiant intensity of a gas burner ame (city gas), tungsten lamp, and the sunlight on

the earth’s surface, along with UVTRON spectral response characteristics. As this gure shows, the UVTRON has no

sensitivity in the visible range and is only sensitive to ultraviolet light in a very narrow region of spectrum.

TPT B0009EB

200 300 400 500 600 700 800 900

100

IR REGIONVISIBLE REGIONUV REGION

WAVELENGTH (nm)

TUNGSTEN

LAMP

GAS

FLAME

SUNLIGHT

UVTRON

SPECTRAL

RESPONSE

RELATIVE SENSITIVITY, RELATIVE INTENSITY (%)

Various Types of Spectral Radiant Intensity

TPT B0009EB

Figure 1: Typical Spectral Radiant Intensity

The UVTRON is a sensor sensitive only to ultraviolet light with wavelengths shorter than 260 nm. Featuring high

sensitivity high output, and high-speed response, the UVTRON is the ideal sensor for detecting ame and electrical

discharge phenomena.

STRUCTURE AND BASIC OPERATING PRINCIPLES

The UVTRON is a bipolar tube with a structure similar to that of a phototube. Just as with phototubes, the UVTRON

utilizes the photoelectric emission effect, but the inside of the UVTRON tube is lled with special a gas rather than be-

ing a vacuum, so it operates as a discharge tube. Figure 2 shows its structure and a schematic diagram of operation. A

voltage is applied across the anode and photocathode (cathode) which is only sensitive to ultraviolet light. When UV

light passing through the UV glass (UVTRON bulb) strikes the cathode, photoelectrons (electrons) are emitted from the

cathode surface due to the photoelectric emission effect. These photoelectrons are then drawn to the anode by the elec-

trical eld created by the supply voltage. If the supply voltage is low, the operation is the same as for a phototube and

the current, i, is extremely weak. When the voltage is increased to strengthen the electrical eld, the photoelectrons are

accelerated so they collide with the gas molecules within the tube and ionize them. The electrons produced by ionization

continue to collide with other gas molecules while causing ionization until they nally reach the anode. Meanwhile, the

positive ions are accelerated towards the cathode and the resulting collisions with the cathode generate a great number

of secondary electrons. As this cycle is repeated, a large current suddenly ows between the anode and cathode, creating

an electrical discharge. This phenomenon is called gas multiplication and the voltage at which this discharge starts is

called the discharge starting voltage Vl of the UVTRON.

Once the electrical discharge has begun, the tube is lled with electrons and ions and the voltage that maintains the

discharge drops to a low value. This value is called the discharge sustaining voltage Vs. Figure 3 shows this state. The

UVTRON primarily operates in the glow discharge region, but in this region, since the discharge sustaining voltage Vs

is lower than the discharge starting voltage Vl, the discharge will continue unless some means is employed to control

the supply voltage.

TPT C0010EA

+–

HIGH VOLTAGE Ebb

DISCHARGE

CURRENT

TUBE VOLTAGE V

CURRENT LIMITING

RESISTANCE

PHOTO-

ELECTRONS

FROM IONIZATION

CATHOD

(PHOTOCATHODE)

UV LIGHT

FILLED GAS

UV GLASS

ANODE

Schematic Diagram of UVtron Operation

Figure 2: Schematic of UVTRON Operation

TPT B0029EA

10-6 10-4 10-2 1102

Ebb

DISCHARGE CURRENT i (A)

GLOW DISCHARGE REGION

OPERATION

POINT

Rs LOAD LINE

TUBE VOLTAGE (V)

UVtron V-I Characteristics

Figure 3: UVTRON Voltage-Current Characteristics

UVtron DRIVE CIRCUIT

Operating a UVTRON requires a high voltage of about 350 V. Figure 4 shows the basic circuit for the DC-DC con-

verter high-voltage power supply and the operating waveforms for each part. In this case, it is important to lower the

converter oscillation frequency, f, to reduce the capacitance of capacitor C1 for smoothing the rectied high voltage, and

to raise the power supply output impedance. Here is an explanation of the operation of this circuit. (See Figures 4-1 and

4-2.)

Point (a): This is the converter oscillation waveform. Pulses with a width of a few microseconds are generated at in-

tervals of a few milliseconds to a few tens of milliseconds.

Point (b): The height of pulses is raised in proportion to the winding ratio for the step-up transformer.

Point (c): High DC voltage Ebb is supplied to the UVTRON's anode by rectier diode D and smoothing capacitor C1.

Point (d): Discharge starts when ultraviolet light enters the UVTRON. The charge on C1 begins to ow as discharge

current, i, to generate narrow voltage pulses across R and C2.

Point (e): The charge on C1 is exhausted, the anode voltage falls below the discharge sustaining voltage Vs, and the

discharge stops. The anode voltage does not recover until the next charge. During that period, the ions in

the UVTRON are quenched.

Point (f): If no ultraviolet light enters the UVTRON, the anode voltage recovers to Ebb, and there is no discharge un-

til ultraviolet light is received.

The UVTRON repeats this cycle to indicate the presence or absence of ultraviolet light with pulse signal output.

Here, it is important that the converter oscillation interval (l /the oscillation frequency f) be greater than the time re-

quired for the ions generated in the UVTRON tube by the discharge to be quenched, so this interval must be from 5 to l0

milliseconds. This period is called the quenching time. Also, since the capacitance of smoothing capacitor C1 inuences

the discharge current, it is best to reduce the capacitance of C1in order to retard the wear on the electrodes and to reduce

the number of ions generated. The optimum capacitance is a few tens of picofarads.

–

C2R

UV TRON

(a)

(c)(b)

(d)

TPT C0011EA

UVTRON OUTPUT

WAVEFORM

OSCILLATION

WAVEFORM

OSCILLATOR

CIRCUIT

UVtron Drive Circuit

Figure 4-1: UVTRON Drive Circuit

(d)

(c)

(a)

(b)

(e)

(f)

Ebb

0 V

f=1/T1

TPT C0012EA

DISCHARGE

SUSTAINING VOLTAGE

INCIDENCE OF UV LIGHT

UVTRON

OUTPUT WAVEFORM

UVTRON

ANODE VOLTAGE

STEP-UP TRANSFORMER

VOLTAGE WAVEFORM

DC-DC CONVERTER

OSCILLATION WAVEFORM

UVtron Operation Waveforms

Figure 4-2: UVTRON Operation Waveforms

SIGNAL PULSES AND BACKGROUND

When the UVTRON is operated with the circuit shown in Figure 4-1, the number of output pulses is increased in

proportion to the incident light intensity at low light levels. However, it will be saturated at the converter oscillation fre-

quency f, as shown in Figures 5 and 6. Because of these characteristics, the UVTRON is better suited for on-off opera-

tion that determines whether or not ultraviolet light is present, rather than for precise measurement of light level.

The next point that must be considered is the background (BG). The BG is caused by sporadic discharges that occur

due to radiation such as cosmic rays and static electricity, even if no ultraviolet light enters the UVTRON. Figure 6 also

shows this phenomenon. When detecting ultraviolet light with the UVTRON, the BG causes false operation if the output

pulses are directly used as the detection signals. Therefore, the signal must be processed to cancel out this background.

Figure 6: UVTRON Output Pulses

Figure 5: UVTRON Sensitivity and Background

010-14

100

(BG)

101

102

103

10-13 10-12 10-11

λ: 200 nm

1200/min.

TPT B0030EA

INCIDENT LIGHT INTENSITY (W/cm2)

LIGHT LEVEL EQUIVALENT TO

LIGHTER FLAME (25 mm) AT 5 m

(SATURATION)

STANDARD TYPE

HIGH SENSITIVITY

TYPE

DC=DC CONVERTER

f=20 Hz

UVtron OUTPUT PULSE (min-1)

UVtron Sensitivity and Background

10 s to 1000 s

0.2 s to 1 s

50 ms

TPT C0013EA

RANDOM

LOW LIGHT LEVEL

Ex.: Lighter flame

(25 mm)

at 5 m away

NO UV LIGHT

(BG)

UVtron Output Pulses

SATURATION

LIGHT LEVEL

DC-DC CONVERTER

f=20 Hz

SIGNAL PROCESSING CIRCUIT

Since the UVTRON output pulse waveforms are the same for incident ultraviolet light and for background noise, the

waveforms cannot be distinguished. Therefore, the pulse generation frequency (interval between pulses) is used to can-

cel out the BG. Figure 7 is a block diagram for the signal processing circuit and Figure 8 is a timing chart for its opera-

tion. The operation of this circuit is explained below.

Point (a): The output pulses from the UVTRON are input to the gate timer and the counter at the same time. The

counter counts the pulses sequentially.

Point (b): The gate timer maintains the open state as long as the pulses enter in succession at time intervals shorter

than the setting time T1. When the pulse interval is greater than T1, the gate timer closes the gate and resets

the counter.

Point (c): When a series of pulses are input, the counter adds them up. When the number of pulses reaches the setting

value, a pulse is generated to the output circuit and the counter is reset.

Point (d): At the output circuit, the output pulses from the counter are lengthened to the necessary time interval (T2)

and are output.

*1 (Figure 8): The setting time T1 must be shorter than the interval at which background noise pulses are generated. It is

usually safe to set T1 to 5 seconds or less. If set too short, weak ultraviolet light cannot be detected.

*2 (Figure 8): The sensitivity of the device can be adjusted by the counter setting. To trigger the device with weak ultravio-

let light, set the counter to 10 or less. To have the device only detect higher intensity of ultraviolet light, or

to have the device operate for weak ultraviolet light if it is received for a long period of time, set the counter

value to more than 10. If the counter value is set to 3 or less, the BG may not be cancelled out, so use caution.

5 V

GND

–

10 µs

10 V

0 V

T2(10 ms)

(d)

(a)

(c)

(b)

1000 pF 10 k

TPT C0014EA

UVTRON

CATHODE

UVTRON OUTPUT PULSE

GATE TIMER

RESET

OPERATION SENSITIVITY

SETTING SWITCH

COUNTER

OUTPUT SIGNAL

WAVEFORM

OUTPUT

CIRCUIT

Signal Processing Circuit

Ω

Figure 7: Signal Processing Circuit

10 µs

T1(2 s) *1

2 s 2 s

1111

000

(c)

(b)

(a)

1 µs or less

10 ms

TPT C0015EA

SIGNAL OUTPUT Q

COUNTER LEVEL

PATTERN

COUNTER

RESET

UVTRON

OUTPUT PULSE

GATE TIMER

(Ex.) When 3 pulses enter in succession within an interval

of 2 seconds, a pulse with a width of 10 ms is output

as the signal output.

Operation Time Chart for Signal Processing Circuit

Figure 8: Operation Time Chart for Signal Processing Circuit

SUPPLY VOLTAGE AND SENSITIVITY

Figure 9 shows a typical relation between the supply voltage and the UVTRON sensitivity. The UVTRON is more

sensitive as the supply voltage is increased, but this also increases the background noise. Keep the supply voltage within

the recommended range.

-10 %

100

150

200

+10 %

TPT B0031EA

CHANGE IN SUPPLY VOLTAGE

(Recommended Value)

RELATIVE SENSITIVITY (%)

Supply Voltage and Sensitivity

Figure 9: Supply Voltage and Sensitivity

WEB SITE www.hamamatsu.com

Information in this manual is current as of Oct. 2008. Specifications are subject to change without notice due to product improvement, etc.

For the latest information, please contact us at the address below.

HAMAMATSU PHOTONICS K. K., Electron Tube Division

314-5, Shimokanzo, Iwata City, Shizuoka Pref., 438-0193, Japan, Telephone: (81)539/62-5248, Fax: (81)539/62-2205

U.S.A.: Hamamatsu Corporation: 360 Foothill Road, P. O. Box 6910, Bridgewater, N.J. 08807-0910, U.S.A., Telephone: (1)908-231-0960, Fax: (1)908-231-1218, E-mail: [email protected]

Germany: Hamamatsu Photonics Deutschland GmbH: Arzbergerstr. 10, D-82211 Herrsching am Ammersee, Germany, Telephone: (49)8152-375-0, Fax: (49)8152-2658, E-mail: info@hamamatsu.de

France: Hamamatsu Photonics France S.A.R.L., 19, Rue du Saule Trapu, Parc du Moulin de Massy, 91882 Massy Cedex, France, Te lephone: (33)1 69 53 71 00, Fax: (33)1 69 53 71 10, E-mail: info[email protected]

United Kingdom: Hamamatsu Photonics UK Limited: 2 Howard Court, 10 Tewin Road, Welwyn Garden City, Hertfordshire AL7 1BW, United Kingdom, Te lephone: 44-(0)1707-294888, Fax: 44-(0)1707-325777, E-mail: info@hamamatsu.co.uk

North Europe: Hamamatsu Photonics Norden AB: Smidesvagän 12, SE-171-41 SOLNA, Sweden, Te lephone: (46)8-509-031-00, Fax: (46)8-509-031-01, E-mail: info@hamamatsu.se

Italy: Hamamatsu Photonics Italia S.R.L.: Strada della Moia, 1/E 20020 Arese (Milano), Italy, Telephone: (39)02-935 81 733, Fax: (39)02-935 81 741, E-mail: info@hamamatsu.it

TPT 9001E02

JAN. 2009WD

PRECAUTIONS WHEN USING THE UVTRON

(1) Installation

When the UVTRON discharges, it emits ultraviolet radiation. If two or more UVTRONs are used in close

proximity, they must be arranged so that they will not interfere with each other optically.

(2) Humidity

Humidity around the UVTRON leads may cause leak current, dropping the anode voltage and stopping the

UVTRON from operating. In particular, if dirt or dust gets on the leads, it easily absorbs moisture, so keep the area

around the leads clean.

(3) Dirt on the window

Since the UVTRON operates at high voltage, static electricity causes dust to build up on the surface of the glass

bulb. This will lower the ultraviolet transmittance and UVTRON sensitivity, so periodic inspection and mainte-

nance is necessary, such as wiping off with gauze moistened with alcohol.

(4) Soldering

When mounting the UVTRON on a printed circuit board, solder the leads quickly (soldering iron tip temperature:

350°C for less than 5 seconds). If the leads are heated excessively, the glass may crack or the UVTRON

characteristics deteriorate. After soldering, wipe away the solder ux with alcohol, etc. The ux residue absorbs

moisture which may cause current leak, dropping the UVTRON supply voltage and stopping the operation. When

using a UVTRON with hard pins, use the mating sockets available from Hamamatsu Photonics.

(5) Vibration and shock

The UVTRON is designed to pass vibration and shock tests in compliance with IEC 60068-2-6 (sinusoidal

vibration test – R9454, R9533: 3.0 mm peak to peak, 200 m/s2,10 Hz to 2000 Hz; other types: 1.5 mm peak to

peak, 100 m/s2, 10 to 500 Hz) and IEC 60068-2-27 (shock test - R9454, R9533: 10000 m/s2, 1 ms; other types:

1000 m/s2, 11 ms). However, if the UVTRON is subjected to excessive shock such as dropping, the glass bulb may

crack or the internal electrode may be deformed, resulting in poor electrical characteristics. So use extreme caution

when handling the UVTRON.

(6) Polarity

The UVTRON has a cathode and an anode, so connect them with correct polarity. Reverse polarity connection

causes malfunction or breakdown.

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