IE842516L - A photoelectric control unit - Google Patents

Description

SS885 1A A PHOTOELECTRIC CONTROL UNIT The invention relates to a controller for a photoelectric control unit and in particular to a controller for a photoel@cts.lc control unit foe a lamp such as a street l&mp.

The controllers for lighting control units which are presently available on the market are either electro-mechanical, electronic or a combination of both. Electro-mechanical units switch power to a load by opening or closing a pair of heavy duty electrical lo contacts. Generally the line voltage has a peak value of over 310 volts which causes arcing across the contacts as they open and close. The arcing in turn causes pitting o£ the contact surfaces resulting in a short useful life-span for the controller.

A farther problem with conventional controllers is that in time, the light-level threshold can drift outside the specified limits due to drift of the threshold reference value and changes in the characteristics of the light detecting sensor which is normally a light dependent 20 resistor or LDR. Conventional units employ a thermal switching technique where the LDR controls the current through, and thus, the temperature of a bi-metallic strip. The threshold point is determined by the force required from the thermal strip to change over spring 25 loaded electrical contacts. The characteristics of the spring load as well as those of the bi-metallic strip change with time and this causes the accuracy of the unit to drift outside the acceptable limits. Also, the LDR is required to conduct large currents to heat the 3q bi-r.etallic strip and the resulting self-heating effect causes the LDR to change its characteristics over a period. The LDR units commonly used in existing controllers, gradually break down allowing moisture and 2 impurities to effect the selenium cell. This combined with temperature rise in the device contributes to further drift o£ the light level threshold.

This invention is therefore directed towards providing 5 a controller for a photoelectric control unit which will minimise pitting of the contact surface and hence prolong the useful life of the unit.

The invention provides a controller for a photoelectric control unit, the controller comprising a photoelectric 10 sensor, comparing means for comparing the Intensity of sensed light with preset light intensity and switching means operated by the comparing »eans to switch a lamp, said switching means comprising a switch which operates over a large voltage range.

In one embodiment of this aspect of the Invention the output is a street lamp.

In a particular preferred embodiment of the invention the switch comprises a relay triac electrically connected in parallel. Typically the triac is provided 20 in a triac control circuit which is operated by the comparing means„ On switching of the switch, the relay conducts at low voltages and the triac conducts at high voltages.

In one embodiment of the invention the photoelectric 25 sensor comprises e light sensitive resistor whose resistance increases with the intensity of incident light.

Preferably the controller includes a capacitor which is charged when the triac operates to keep the relay closed £or a short period to ensure continuous conduction. 3 In another preferred embodiment of the invention the photoelectric sensor comprises a phototransistor.

The invention will be more clearly understood from the following description thereof given by way of ©sample 5 only with reference to the accompanying drawings in which:- Figurs 1 is an esploded perspective view of & photoelectric control unit according to the invention, Figure 2 is a perspective view of the photoelectric 10 control unit of Figure 1, assembled, Figure 3 is a diagrammatic side view illustrating the unit of Figures 1 and 2 in use, Figure 4 is a side, partially cross-sectional view of the control unit of Figures 1 and 2, Figure 5 is a perspective view from above of a portion of the control unit, 4 Figure 6 is a perspective view of a socket housing attachment for use with the control unit of Figures 1 and 2, Figure 7 is a perspective view of a control unit with 5 the housing of Figure 6 attached, Figure 8 is a side cross-sectional view of the control unit with the housing attached, and Figure 9 is a circuit diagram of a controller for a photoelectric control unit. lO Referring to the drawings and initially to Figures 1 to 5 thereof there is illustrated a photoelectric control unit according to the invention and indicated generally by the reference numeral 1. The control unit 1 comprises control means, in this case mounted on a 15 printed circuit board 2 for switching an output, in this case a street lamp 3. The control means as will be described in more detail below, includes a photoelectric sensor which causes power to the lamp 3 to be switched off when the amount of light falling on 20 the sensor exceeds a pre-set value, in this case 55 lux. The sensor is mounted on the printed circuit board 2 and electrical connection means between the printed circuit board :and lamp 3 is provided by three connector pins 4 which are shaped at their lower 25 ends 5 to engage in a twist-socket provided on the lamp 3. The connector pins 4 are connected at their upper end 6 to connection points (not shown) on the printed circuit board through flexible connecting wires 7. The connections between the connector pins 4 and printed 30 circuit board 2 are capable of withstanding vibrations and/or shudder which would normally be encountered in use with street lanterns.

To prevent overheating of the connector pins 4 and consequent malfunctioning and possible damage to the electrical components mounted on the printed circuit board 2 the pins 4 are led through a cooling means in the fossa of a stem which in this case is defined by a cooling chamber 8 where heat generated in the pins 4 is dissipated through the walls of the chamber 3.

Referring particularly to Figure 5 the cooling chamber 8 comprises & cylindrical side-well 10 and a disc-shaped base wall 11 which extends radially outwardly of the side wall 10. A shirt 12 extends axially downwardly from the outer extremity of the base wall 11. The base wall 11 is formed with three holes 13 which are equispaced apart at 120" and through which the connector pins 4 are led. As will be apparent particularly from Figure 1 each of the connector pins 4 is cranked at 15 and 15 to define an axially depending leg portion 17, an interconnected radial at base wall portion 18 and an axially extending side wall portion 19. Each of the pins A is retained in position in a retaining hole 14 by a self-tapping screw 21 which extends through the-hole 14 to engage in a corresponding hole 22 in the base wall extending portion 18 of each connector pin 4. The connector pins 4 ®ea sized and shaped so that a large surface area of the connector pins 4 is in contact with the side and base walls 10, 11 of the cooling chamber. Consequently heat generated in the connector pins 4 is dissipated through the walls of the chamber 8. To fissist heat transfer the cooling chamber 8 is also substantially filled with a heat transfer medium, in this case in the form of a potting compound 24 which conducts heat away from the pins 4 and into the side and base walls 10, 11 of the cooling chamber 8. The potting compound used may be any suitable incapsulating compound having a high thermal conductivity such as a Humise&l 2B74. 6 A sealing ring gasket 27 which is usually o£ neoprene material is provided on the base wall 11 of the cooling chamber 8 to prevent ingress of moisture and dirt through the joint between the cooling chamber skirt 12 5 and the socket provided on the lantern 3.

It will be appreciated that the cooling chamber defines a stew, which both raises the assembly from the hot parts of the lantern and minimises the heat carried by the connectors to the electronic components mounted on lo the printed circuit board. In tests, in which the control unit was mounted on a 400 watt lantern at room temperature, the use of the cooling chamber was found to reduce the temperature of the connector pins at the PCB connection points by up to 10" which represents a 15 large improvement in reliability.

The printed circuit board 2 is mounted in a printed circuit board housing 30 which comprises a substantially disc-shaped base 31 and a cylindrical side wall 32 extending axially upwardly from the base 31. Three 2g connector pin receiving slots 33, equi-spaced at 120°, extend through the base 31. Three screw receiving pillars 34 extend upwardly from the base 31 adjacent to side wall 32 and are also equi-spaced at 120" around the housing. Each of the pillars 34 is formed with a 25 hoi® 35 for reception of a self-tapping screw 36 which extends through corresponding holes 37 in printed circuit board 2 for mounting the board 2 to the pillars 34. Reinforcing webs 38 extend between each pillar 34 and the side wall 32.

The upper rim of the circuit board housing side wall 32 is formed with a step portion 39 for reception of a complementary step portion 40 which extends around the 7 lower periphery of a translucent conical cover <11 through which light passes to the photoelectric sensor on the printed circuit board 2. The canopy or cover 41 is of conical shape to prevent accumulation of dirt and 5 also discourage birds from perching on the cover. The cover is typically of a plastics material which is treated to protect against ultra-violet light. For fitting the printed circuit board housing 30 and cooling chamber 8 together the housing 30 is formed 10 with a socket which in this case is defined by a skirt 45 which extends axially downwardly approximately mid-way across the base for reception of a spigot defined by the upper edge of the side wall 10 of the cooling chamber 8.

To prevent ingress of dizt and moisture, the component parts of the control unit are securely fixed together and the unit is then coated with a sealing compound to provide additional defensive measures against moisture and dirt ingress. 2o advantage of the invention is that the connection means between the control means and the output is arranged to dissipate any heat generated and hence protect the components of the control means. Thus, a more efficient and reliable switch which has a long 25 life in use is provided.

Referring to Figures 6 to 8 there is illustrated a modified photoelectric control unit which is smaller to that described above with reference to Figures 1 to 5 and like parts are assigned the same reference 30 numerals. In this case the unit includes an electrical socnet receiving housing 50 for housing an output socket 51 which is connected at one end to the connector pins 4 and which is connected through an e outlet cable 52 to the output which it is desired to switch such as a street or security lantern. The housing 50 includes an upper radial wall 53 and an axially upwardly extending side wall portion 54 which 5 defines a spigot £or insertion in the socket defined by the skirt 12 of the cooling chamber 8. A lower cylindrical side wall portion 55 extends downwardly from the upper wall 53 of the housing 50. The lower side wall portion 53 of the housing 50. The lower side 10 wall portion 55 is turned inwardly to define a base wall 56 having a central opening 57 through which the electrical connection lead 52 is led from the socket 51 for connection to an output. The socket 51 is carried by a mounting plate 60 which is fixed in position by 15 self-tapping screws 61 which engage in corresponding screw receiving portions 62 which extend downwardly from the upper wall 53. The sealing ring gasket 27 seals the joint between the cooling chamber skirt 12 and the socket receiving housing 50.

Mounting means for mounting the control unit on a fixture such as a wall is in this case provided by a mounting flange 65 which is connected to the socket receiving housing side wall 55 by a connecting web 66. The flange 65 is formed with two axially extending slots 67 for ease of mounting to a fixture. The particular advantage of the control unit for a photoelectric switch according to this embodiment of the invention is that by using the electrical socket receiving housing attachment 50, the control unit may be used in a wide range of applications including security lighting and in other applications where it may be necessary to mount the control unit on a fixture such as a wall rather than directly on a lantern. 9 R«f®rHn<5 to fig. 9 there 1s Illustrated a circuit d1eg» rai: of a controller for us® with o photoelectric switch such es this photoelectric switch described abova with reference to Figs. 1 to 3. Th® function of the controller 5 is i',o switch po^er so a lisntara according to the surrounding brightness. The controller comprises a photo®lectric sensor, compering we an:; for comparing th» intensity of sensed light with a preset light Intensity and switching saeans operated the cosapeHng si®cms to switch en output. 1Q The photoelectric ssnsor Is In this ens® provided by & light dependent resistor (LBR) which 1s used to monitor the light level and et specific threshold limits either to close or open the switch. The threshold limits are set to the requlrements of the particular use?.

The switching means 1s 1n this c&se provided by a relay 15 BLl end a trlec TRI1 connected 1n parallel. When it is required to switch the load the triac TRI1 Is engaged and this Is followed a short tiros later by closure of the relay contacts RL1. In this way the relay Rll Is not subjected to high voltages during the switching action and 20 the triac TRII Is not given enough t1®e to heat. Whan the loed 1s to be switched out the relay HL1 is disengaged and this Is followed a short time later by the switching off of the triac TRII. Again the relay RL1 Is removed from the circuit while tha triac TRII Is hold-25 ing the voltage at a low level and the triac TR11 1s not «j1wen <ef»«>agh fin)® to beat. in both af the mtiovn eases th* srlac TSI1 will cease ?e conduct when the relay BL1 shorts "J £ out.

The circuit operates sss follows. A transform®?- TRF1 converts Incoming 220Vrcis (nom) to SSVrsns (ftoa) end this lower AC woltage 1s rectified 6>w a bridge consisting of diodgs D1 to ft®. Capacitor CI Is smoothing capacitor. 2Mdc is shs supply to the remainder of the circuitry.

The I.DR t-esistance is raonitorsd by tan operational erap-lifter A1 through a dlelisy circuit consisting of a capacitor C2 end a resistor R2. This delay9 of (approximately 30 seconds,, prevents abrupt changes in the value of the LDR reaching Al. Thg operational oraplifler 1s ussd in the coui^erate? node and It eosapsrss thg voltage level on thg capacitor C2 with a threshold value ^hich is determined by resistors R3„ R9 and RS. Resistors R3 and R9 fore © potential divider and resistor.R6 provides hysteresis. This Is to.prevent unwanted oscillation during the switching action. Threshold calibration is possible by selecting value for Rsot that will cause the unit to switch at the correct light level. For high reliability tit's voltage across the op-amp must be held at a value less than the mtsnisam rating of the dew Ice. The op-amp Is rated for 36V„ but a voltage of 12V which is provided i toy a treasistor Ql is^ts<sd, A aenes* diode CR1 and a resistor RIO Eiold the base voltage on the transistor Ql at 12® below pall russMl ting In an emitter voltage wMch 1s approximately 11.4V below ruiH. The transistor Ql else acts as * regulaeor, further rsduclng the possibility of oscillatory switching.

Transistors 04 «snd OS nllow the output of op-amp A1 to svitch the relay and the triac. A zener diode CRZ is used to ensures that this transistors Q3 and QS ere switched off when this op-erap output 1s 'Mfih'. The LH301 output Is unable to come within l.S volts of the' rail value 10 ®n<3 would not. therefore,, be ©bis to switch off the transistors Q4 fine) QS. The ssner diodes overcomes this.

During darkness the woliag® on pin 2 of the op-amp is low and the op-ramp output is high. Therefore transistors Ql and QS are switched off during the night 15 and on during the day.

Ths trlec TR11 Is switched through transistors Q4, Q3 sad QS. THi» traasi'itor QS 1s disabled when the transistor- Q4 1s curned on because Its base Is held at the eenifSter voltage. Mhsa the triac TRI1 1s to be turned on 20 the transistor Q4 ceases to conduct allowing negative going pulses from a mains cycle crossover detector, consisting of two transistors (J6 end Q7„ to Influence the transistor Q8. These pulses occur when the mains sine »<awe 1s close to $<gro volts and e««s© the transistor 25 Q8 to qulcfely charge up capacitor CS through the resis- 1s?or R22. The voltage at the base of the trisnsslster QS then esecwsiffiS high enough to switch on the sriec TRI1. the resistor R24 which 1s connected between the gets o? the sriac tall ®nd the eMltter of the transistor Q9 serves 5 SO Halt the current through the transistor QS to a reliable level. The resistor 822 also Units the peaft cure-ant through the transistor Q8 to a reliable level. When the triac TKI1 is to be switched Off the transistor Q3 starts conducting thus disabling the transistor QS. The voltage on lO the base of the transistor Q9 now begins to decrease as the energy on the capacitor CS is discharged through the resistor R23. After a tisae delay the voltage on the transistor QS base «111 be too low to staintain the triac TKI1 in conduction. This tlwe delay 1s needed for 15 the triac/relay sequencing function and It provides sufficient time to allow the relay to disengage before the load voltage increases.

For Increased reliability and to reduce radio Interference this triac TBI! is switched during the raa1ns zero 20 crossovsr points. These are detected by means of transistors QS and t>>". The ffiffiins is set-spied through a resistor R20 and United by a saner diode CK3 and a diode D9. The resulting waveforn the® arrives at the base of the transistor QS 1s ©ppi*os1®ately square and is further squared 25 by she transistor Q6. A differentiator network consisting of a capacitor C3 and a resistor R14 provides a negative 13 golft^ pulse ffi.acSi tisae thai! vcHegs on the collector of tEie transistor 05 sia&es the transition from rail so ground. This transition reprssssnts the sero cross point when the main cycle Is going from ensgetlwa to 5 positive. In a similar manner this transistor Q?„ capacitor C4 and resistor R18 will generate a puis® during the positive to negative raelfts cycle transi tlon. Diodes D7 land 08 ensure that only the negative going pulses are trsnsnltted to this base of ths tr«ns1stOF OS.

T^a relay RLl is operated through transistors 05 end Q10. The relay RLl Is of the normally on type and whgn the bnse vol tags of the transistor Q10 is low tha switch will be clossd. When the relay RLl Is to be engaged the transistor QS will cease to conduct. The voltnge on the capacitor 15 C5 will then begin to decrease as It 1s discharged through the resistor R12. After is delay dictated by the capacitor CS and the resistor R12 the bes<s voltnge of the transistor Q10 will go below the Mlnlnun holding value for the relay 2o RLl ^nd the rslay contacts close. This delay 1s needed to allow 6h« fcrlaci, TRI1 which is being switched simultaneously,, tlrae so reduce she voltage across the relay contacts to an acceptable level. This Is part of the trlac/reley sequencing function. Uhen the relay RLl 25 is to has disengaged (at scorning) the transistor QS again conducts. charging Mp the capacitor C5 quickly. The relay RLl "3s then opened quickly before the triac TRS1 is disengaged. thus protecting the jtwlseh contacts, diodes 05 and 08 protect the transistor Q10 fro® the back end that normally ■jk »ce0i»|s>»s»1lces th<s switching of a relay. A normally 'on' pet®" Is tsssd here so that In She evens of failure she sr. rieet '8 a tit erst (xtl ng controlled will be switched on pgnaawsatlw. It is enpectsd that saost failures within the 5 control lige* will result in less of power to tha relay end the controller will thus west the requirement that the lantern be switched en. Varistor protection is ©snployed in the circuit to prevent large ®ains bourne spikes and transitions getting to the circuitry. A varistor. 6H1, is 10 placed after the mains transformer TRF1 end takes advent* age of the transformer's secondary resistance. The waris-tor's resistance decreases significant!y as the voltage across it increases and this 1a used to lira-it tha voltage at the transformer secondary. The transformer„ TRF1, 15 because of its inherent winding reslstances will not be d&oag@d by the extra load pieced on it during line transients. A varistor is used here in preference to a zener diode; (Because of its greater sp®<ad a tit? current handling capabilities. 2o LOR self heating is reduced toy minimising the power dissipation vfthln the controller through tha use of high external resistor values. Power dissipation is approximately 10nw. The use of transistors allows tha voltage on the LDR to fjis oeasured despite the high source Impedance 25 due to this large resistor values. Any suitable LDR way be ms«<S aarf preferably the LOS should tie htrmetlcally ssalad to ensure that triestupe ernd Impurities cannot enter the LOU <sad algfsr fes eharactertlstics. The particular LDR chosea the CLH5KGM device uhlch has » stable light to resistance relationship after 100 hours burn-In. All transistors are typieelly typ® 0C£37B-S2 whll® ell PNP transistors are typically type BC2128-S2. All 5 resistors ar® usually jy.jgs carbon. The elements; designated ?! *re typically solid aluminium <®0V and those dssignat-<3d ® are usually long life aluminium electrolytic ELCO series, A coafonii&l coating compound may be Applied tc both the 10 bonrd and the components to ensure rigidity of tha components during heavy vibrations or lentera mast shudder, to protect the electronic circuit from impurities from moistures and dirt Ingress and to further protect the board and the components from uv radiation through the 15 conical canopy or cover. As ultra-violet tends to break down plastic. both the housing and the conical are doped with is recomended U,w. Inhibitor. The use of ft relay assisted triac overcomes the problem associated with the switching of hea-vy loads. When relay contacts open 2Q Of closas arcing will occur between the relay contacts at-id tftfs Mill, In time, cense ths contacts to become pitted and eventually non-operational. The arcing problem could be overcome using a semiconductor switch In the form of a triac or transistor. However, such en arrangement 25 because of its saturation voltage dissipates power resulting In heating. This heating will severely curtail the reliability of the device. Thus, the controller according to this aspect of the invention is particularly reliable in use and greatly increases the useful life of a photoelectric control unit. The 5 method of switching using a relay assisted triac has been tested by subjecting a prototype to 40,000 switching operations which is the equivalent of over 100 years operation , and when examined after the test the relay way found to be in excellent condition lo without any signs of pitting.

A phototransistor may be employed as photoelectric sensor instead of the LDR used in the embodiment described above. 17

Claims (9)

1. A controller for a photoelectric control unit, the controller comprising a photoelectric sensor, comparing means for comparing the intensity of sensed light with preset light intensity and switching means operated by the comparing means to switch a lamp, said switching means comprising a switch which operates over a large voltage range.

2. A controller as claimed in claim 1 wherein the lamp is a street lamp.

3. A controller as claimed in claims 1 or 2 wherein the switch comprises a relay and a triac electrically connected in parallel.

4. A controller as claimed in claim 3 wherein the triac is provided in a triac control circuit which is operated by the comparing means.

5. A controller as claimed in claim 3 or 4 wherein, on switching of the switch, the relay conducts at low voltages and the triac conducts at high voltages.

6. A controller as claimed in any of the claims 3 to 5 including a capacitor which is charged when the triac operates to keep the relay closed for a short period to ensure continuous conduction.

7. A controller as claimed in any of claims 1 to 6 wherein the photoelectric sensor comprises a light sensitive resistor whose resistance increases with the intensity of incident light. -18-

8. A controller as claimed in any of claims 1 to 6 wherein the photoelectric sensor comprises a phototranslstor.

9. A controller for a photoelectric control unit substantially as hereinbefore described with reference to Figure 9 of the accompanying drawings. Dated this 14th day of October 1985 CRUICKSHANK & CO., Agents for the Applicant, 1 Holies Street, Dublin 2.