Application & Guidance Notes

Transcription

1 Phooelecric Swiches Applicaions Successful applicaion of phoo-elecrics ino sysems need no involve a deep undersanding of heir principles of operaion. Following hese few simple rules will enable many of he likely pifalls o be avoided. For more complicaed applicaions, IMO provides a full applicaions advice service. In cases of uncerainy IMO will loan phooelecric swiches o ry ou on a paricular process. Selecion Crieria The following poins mus be known before he mos suiable swich can be seleced.. Deecion mehod Through-beam (separae ype) This ype has a separae ransmier and. I will deec any objec large enough o break he beam. Avoid using his syle of swich o deec ransparen objecs, since he ligh beam will pass hrough he objec wihou breaking he beam. Diffuse ype This ype has a ransmier and in one head. I works on he principle of ransmiing a beam of ligh and deecing reflecions from he objecs o be deeced. Since all colours will reflec some ligh i can be used o deec almos all ypes of objec, hough a closer range han separae ypes. I is paricularly suiable for deecing ransparen objecs, such as boles. Avoid using his ype where here is a background close o, or more reflecive han he objec, since his background will also be deeced. Fixed-focus These are similar in operaion o he Diffuse ype. However, hese models will ignore boh background and foreground objecs. Deecion of objecs hrough a ransparen cover Typical examples: () Deecion of he conens in a ransparen case. () Deecion of he posiion of meer poiner. Reroreflecive ype This ype works on he same beam-break principle as he hrough-beam ype. However, in his case boh ransmier and are housed in he same body, and he ligh beam is bounced off a prismaic reflecor which reflecs ligh back in he direcion from which i came. This is paricularly imporan for ease of alignmen. I has he advanage ha only a single head has o be mouned and wired. I can be used in he same applicaions as for he Separae ype, hough i should no be used o deec objecs ha will reflec ligh, such as polished meal, cellophane or shrink-wrapped packages, since i canno disinguish beween he wo ypes of reflecion. PhooElec// Deecable objec Reroreflecive ype - wih polarised ligh This is a reroreflecive phooelecric swich for use in deecing shiny objecs. I is fied wih polarising filers in fron of he ransmier and lenses, one verical and one horizonal. A prismaic reflecor used wih he phooelecric has he effec of urning he ransmied ligh hrough 9 degrees, hus if he filer in fron of he ransmier only permis verical ligh o pass hrough i, his verical ligh is reurned from he reflecor as horizonal ligh which is allowed hrough he horizonal filer in fron of he lens. If however ligh is refleced from some surface oher han he reflecor i will be reurned as verical ligh and will no pass hrough he filer. Thus reliable operaion is ensured under difficul condiions ha would normally preven he use of a rero-reflecive ype. Such applicaions include shrinkwrapping, and keg handling. No objec presen ligh received Objec presen no ligh received Opical fibre ype This uses an opical fibre as a ligh guide from a remoely-mouned amplifier uni o he objec o be deeced. I is available as hrough-beam or diffuse. An opical fibre phooelecric offers several advanages over a convenional ype: Small size. The deecing head can be fied ino very confined spaces. Sensiiviy. Objecs as small as. mm dia can be reliably deeced. Noise immuniy. The fibre can be roued wih high power cables. Opical fibres can also ofen be aken ino areas where ordinary phooelecrics canno normally be used, such as aerosol filling machines and areas conaining pain fumes. The amplifier can be mouned remoely from he hazardous area, and only he fibre is aken ino he danger zone.. Sensing Range The deecing ranges shown agains each phooelecric on he daa pages are he maximum operaing disance over which he device will work. As a general rule, he shorer he range, he more precise is he deecion. So, firs decide how close he device can be o he objec o be deeced, hen selec a phooelecric wih a range jus beyond his disance. Power Try o selec a phooswich wih a sensing range o sui he applicaion. If an objec can be deeced wih reliabiliy a a range of say, mm, wih no risk of he objec ouching he phoocell a any ime, choose a suiable low power phoocell. Too much power will someimes see righ hrough an objec, or in he case of a Diffuse ype, can reduce effecive resoluion or cause spurious background reflecions.. Objec size and speed Minimum objec size is shown on he daa wih each phooelecric. In high speed applicaions pay aenion o he ime ha he objec will be in fron of he phooelecric. The minimum objec size should be presen for he duraion of he response ime oherwise he objec may no be deeced. Wih hrough-beam and Rero-reflecive swiches, he sandard deecable objec is one which compleely inerrups he ligh beam. Wih Diffuse-reflecion ypes, a whie ma paper is used, of a size defined by individual swich daa. Whie ma paper Square shaped GENERAL Inerference All of he phooelecrics in his caalogue use eiher infrared or visible ligh. As an addiional proecion, i is pulse-modulaed a a high frequency and he is uned o his. IMO phooelecrics are proeced from inerference agains all bu he mos exreme sources of exernal ligh inerference. Advanced circuiry ensures he highes level of immuniy agains elecrical noise. Sabiliy The increasing applicaion of phooelecrics in inspecion processes has led o he developmen of some very sensiive devices, able o

2 Phooelecric Swiches (coninued) discriminae small differences in he colour or size of an objec. When rying o resolve a small difference, here is a empaion o se he sensiiviy of he phooelecric oo close o he swiching poin. This can lead o nuisance ripping under environmenal changes, or as he sysem ages. To avoid his problem, he more sensiive swiches incorporae, a green sabiliy indicaor LED o aid seing up. This lighs when he objec o be deeced is wihin he reliable operaing range of he phooelecric swich, and should always be illuminaed when operaing. The sabiliy indicaor can also be useful where he phooelecric is being used in a dusy environmen, since, as he dus builds up on he lens, he sabiliy indicaor will exinguish, indicaing ha i is ime o clean he lens. Glossary of erms Operaing principle A phooelecric sysem consiss of one or more ransmiers emiing a lighbeam which is direced o one or more deecors (). An elecrical signal is given when his ligh emission is blocked. The emission operaes from an infrared (or red) ligh source which is generaed by high efficiency, low consumpion and long life semiconducors. The emission is modulaed (pulse emission and deecion) for a higher insan operaing power, i.e. higher disances and high immuniy o he ambien ligh. Diffuse phooelecric swich Transmier and are housed in he same uni. The presence of a wihin he sensing range cause he lighbeam o be refleced back o he, hus allowing he deecion. emission/ reflecion diffuse phooelecric swich Rero-reflecive phooelecric swich Transmier and are housed in he same uni. The lighbeam emied by he ransmier is reurned o he via a reflecor. Deecion occurs when he reurn lighbeam from he reflecor is blocked. reflecor ;;; ;; lighbeam ransmier Hyseresis Phooelecric swich hyseresis is he max. difference beween he swich-on poin (non deecion deecion) and he swich-off poin (deecion non deecion) when he approaches and recedes from he sensing head of he phooelecric swich (or from is axis). I is quoed as a percenage of he value of he swich- ON poin. The difference beween he wo swichdisances is inenionally inroduced o avoid undesired swiching when he is jus on he limi of he sensing range. swich ON swich OFF HYSTERESIS Repeaabiliy This is he max. variaion wihin he differen values of he swich-on disance (non deecion deecion) in he same operaing condiions and in shor succession. I is quoed as a percenage of he average value compued for he differen swich-on disances. Tolerance of he sensing range This is quoed as a percenage of he nominal value. The real sensing range is he cenre of his range. Ripple This is he ampliude of he max. admissible ripple in he DC supply volage. I is quoed as a percenage of he sandard DC supply volage. Consumpion This is he maximum curren required a he max. rae of nominal volage. Swiching frequency This is he max. ON OFF changes in swiching sae performed by he phooelecric swich. Wih higher swiching frequency he phooelecric swich is subjec o an ineviable disorion and he ON OFF swiching may no reproduce he sae correcly. Response ime Time inerval beween wo consecuive pulsed emissions. For correc swiching he should be presen wihin he sensing range for a leas his period of ime. The swiching frequency (f) is relaed o he emission range (T) by he formula: f /T. T Deecion mode DIFFUSE RETRO-REFLECTIVE THROUGH-BEAM dark on pulse emission presence deeced signal Oupu ype NPN: due o he oupu ransisor ype, he load is placed beween he posiive and oupu leads. PNP: due o he oupu ransisor ype, he load is placed beween he negaive and oupu leads. : De-coupled oupu (fully isolaed from he supply volage) and NPN/ PNP// userselecable on he single uni. TRIAC: a solid-sae oupu o swich AC volage loads direcly. RELAY: wih oupu relay. Oupu sae The sandard erms for microswiches and inducive s are used o describe he oupu sae a res. - (normally open) - (normally closed) : when deecing a he oupu swiches o he ON sae (conducion). : when deecing a he oupu swiches o he OFF sae (isolaion). If he erminology ligh on/dark on is used, see he able below. ligh on Residual oupu volage This is he volage drop in he swich circui when he oupu ransisor is ON. I is defined as he poenial drop beween ground and oupu erminals for NPN s and beween posiive and oupu erminals for PNP s wih nominal load curren. Leakage curren This is he load curren when he oupu ransisor is OFF wih supply volage a he max. nominal value. emission/ reflecion rero-reflecive phooelecric swich Through-beam phooelecric swich Transmier and are mouned in separae unis opposie each oher. Deecion occurs when he lighbeam beween he ransmier and is broken. F = nd/t T = 6/(r.p.m.) F = nd x (r.p.m.)/6 nd = number of eeh T = roaion period (sec.) r.p.m. Non-repeaing curren peak The non-repeaing curren peak of AC phooelecric swiches is he maximum curren which may flow in he oupu circui for a ime inerval of ms (half a full cycle) and should no be repeaed wihin he lifeime of he, e.g. a curren surge due o a faul. Lower value surges, e.g. inrush currens of conacors, can be oleraed wihou problem, i.e. A max. PhooElec//

3 Phooelecric Swiches (coninued) Proecion agains polariy reversal No damage will occur o phooelecric swiches if he supply wires are reversed. Proecion agains shor circui/ curren limi Shor circui and over-volage proecion operaes by idenifying a max. curren peak or curren limi. When he curren peak or limi is exceeded he phooelecric swich opens he oupu circui. Rese of he operaing sysem is performed in differen ways according o he ype of proecion: a) auorese. The rese occurs auomaically some ime afer he overload has been removed. b) disconnec power o rese. Power mus be disconneced from he swich and re-applied before i will funcion correcly. Proecion agains inducive loads Phooelecric swich oupu wih inducive loads (over-volage) proecion is achieved wih a diode or a Zener diode. Time before swich operaion Time inerval required by he phooelecric swich oupu o become ready afer power has been applied. During his ime he oupu sae is open. This ime is necessary o avoid he phooelecric swich oupu being in an undefined sae, when he sysem is swiched on. Insulaion resisance This is he resisance, expressed in Ω, beween he phooelecric circui and he meal housing or beween he phooelecric circui and he insulaor in which he phooelecric swich is encapsulaed when he housing is made of plasic, when a direc volage of specified value is applied. Dielecric srengh This is he max. value of sinusoidal volage (freq.=5/6 Hz) which can be applied for min. beween he phooelecric circui and he housing (meal) or he insulaor in which he phooelecric swich is encapsulaed (plasic) wihou breakdown of he dielecric used for he circui insulaion. Noise immuniy For DC devices: he maximum noise rae asymmerically applied on he power supply, before any erran swiching. For AC devices: he maximum noise rae applied on he power supply in a common way hrough he wo phases, before any erran swiching. The immuniy rae is compued according o he sandard IEC 8. The es is carried ou by applying pulse rains o he power supply during a ime inerval of min. Every pulse has a rise ime of 5ns and a duraion of 5ns. Several pulses wih a frequency of.5-5khz form a rain of 5ms duraion. Several rains are applied wih a repeiion ime of ms. levels are provided according o he differen pulse ampliude of 5,,, V (I, II, III, IV). Operaing emperaure Temperaure range a which nominal operaing condiions are guaraneed. Inerference by exernal ligh/sunligh This refers o he radiance (quanified in lux) falling on he surface, due o any s illuminaion by lamp or sunligh. The exernal illuminaion causes a variaion in he recepion signal of % of he sandard value when he illuminaion range is lux. However, his value should no be considered o be he limi for he device s correc operaing. Ambien humidiy Relaive humidiy range a which nominal operaing condiions are guaraneed. Excess gain graph This represens he raio beween he signal on he when he, reflecor or ransmier are placed a a disance and he minimum signal necessary o deec he. Expressed as a funcion of he disance. lamp/ sunligh illuminaion gauge Parallel displacemen graph This gives he limi of approach disance Y (non deecion deecion) a which he deecion occurs. This is he posiion of: he (diffuse) he reflecor (rero-reflecive) he (hrough-beam) as a funcion of he disance beween he wo devices. phooelecric swich - diffuse - rero-reflecive - hrough-beam Opical axis angle graph Graph for rero-reflecive and hrough-beam phooelecric swiches giving he sensing range as a funcion of he angle formed by he ransmier axis and he reflecor/ axis. phooelecric swich - rero-reflecive - hrough-beam angle -5 Muual inerference graph This indicaes he possible inerference when insalling several hrough-beam phooelecric swiches side by side. Wihin he inerference area he lighbeam emied by one ransmier may affec he non-corresponding. reflecor ransmier Y reflecor reflecor For a correc applicaion i is necessary o avoid he possibiliy of inerference wih a cerain safey degree. This can be helped by alernaing he posiions of he ransmiers and s. ransmier ransmier Disance/ size graph This graph is suiable only for diffuse phooelecric swiches. I gives he sensing range as a funcion of he dimension for a whie ma paper square. NPN PNP mulifuncion isolaed oupu oupu advanages The oupu is an exclusive innovaion developed for phooelecric and inducive DC s o provice a more flexible alernaive o radiional fixed oupu ypes (i.e. NPN or PNP, normally closed or normally open). Using an opo-isolaor, which isolaes he oupu (DECoupled OUTpu) from supply and deecor circuis, he single uni is able o: perform he possible oupu configuraions, i.e. NPN-, NPN-, PNP-, PNP- (his mulifuncion oupu allows for a large reducion of operaing and socking coss, permiing / reducion of he number of models employed.) perform series/parallel connecions of differen s wihou resricion (for applicaions wih PLC programmable logic his feaure can reduce he number of inpus employed wih a consequen reducion of coss, i.e. by using several s in a logic configuraion, (AND, OR, AND/OR, ec.) on one PLC inpu, he possibiliy of requiring an expansion uni may be saved. Also, he use of several s in a logic circui can simplify he conrol elecronics and save relays.) Descripion Fig. shows he block diagram of a. The oupu sage is elecronically isolaed from he res of he circui by an opo-isolaor. Therefore, he oupu sage may be seen as a simple elecric swich driven by deecor circuiry, bu isolaed from i (fig ). In his way, he oupu is released from he sric logic configuraions NPN or PNP. Y PhooElec//

4 Phooelecric Swiches (coninued) deecion circui deecion circui oupu sae SSR OUT The oupu is also able o swich he oupu sae a res from o and vice versa simply by reversing he polariy of he power supply cables ( - ). Therefore, i is possible o perform all he oupu configuraions, as shown in fig.. NPN/ NPN/ PNP/ PNP/ fig. Oupu sage Fig. shows he oupu sage diagram. I consiss of a power ransisor driven by an opo-isolaor. The Zener diode gives proecion agains inducive loads. Shor circui proecion is ensured hrough a check of he load curren. When overload or shor circui occur he oupu ransisor is inhibied (see diagram shown in fig. 5). V SAT (V) FC Sauraion volage / Load curren fig. 5 TA =5 C T D 5 5 I L (ma) T Series connecion The figure shows a simplified diagram of series connecion of a number of s. The maximum number of s (n) o be conneced is obained from he following formula: I LIM (ma) Z OUT - SUPPLY fig. SUPPLY fig. OUT () OUT (-) Oupu curren limi/ Temperaure POWER SUPPLY fig TA ( C) fig. 6 LOAD n Where: V Load ON V Power supply V sa VPower supply VLoad ON Vsa Vsa Vsa Vsa x n min. load energizaion volage supply volage sauraion volage of he in ON mode (.8-.V, see fig. 6). In series connecion of several s i is necessary o accoun for he volage drop value when he load is energized (V sa ranges beween.8 and.v, as shown in fig. 6), according o he available supply volage. Parallel connecion The figure shows he simplified diagram of parallel connecion of a number of s. LOAD VLOAD Lleakage = µa N The maximum number of he s (n) o be conneced is obained from he formula: n = V Load OFF / (R Load x L leakage ) Where: V Load OFF max. load de-energizaion volage R Load load resisance L Leakage max. leakage curren of he (µa). Since he value for leakage curren is very low here are no pracical resricions in he parallel connecion of several s, provided he load curren is of a few ma. Applicaion examples The following examples show simple logic configuraions. For a beer undersanding of hese, consider ha: a) n ruh-able and indicae he acual oupu configuraion ( open - closed). The presence is shown by he shaded areas. b) a in column indicaes an energized load. c) he equivalen logic diagrams are shown, wihou NPN or PNP load connecion, for easy undersanding.. Series/parallel combined connecion. Series conneced oupus ( oupus) Separae power supply Parallel/series connecion N.C. N.C. AND funcion wih invered inpu NPN NPN PNP -VDC 5-VDC V LOAD V SUPPLY MA. ISOLATION BETWEEN V LOAD AND O V SUPPLY: VAC The decoupled oupu allows differen volages from separae power sources o supply he and load. This enables he user o mee all inerface applicaions. n = (V Power supply - V Load ON ) / V sa PhooElec//

5 Phooelecric Swiches (coninued) Se up procedure for self each produc ypes RD, RP, RJ, FP and FG Adjusmen a he ouch of a buon... Needing no special skills, simply press o acivae he self-each funcion and configure parameers insiu. The lock keyboard funcion prevens unauhorised or accidenal reseing of sensiviy. LO-DO LED display A-a-glance indicaion of: ON-OFF deecion diry opic low signal alignmen imer ON locked keyboard shor circui Keyboard Three waerproof keys are used o adjus and se: hreshold/sensiiviy iming (from. o 5secs) oupu sae keyboard lock Keyboard use There are hree mehods o acivae he keys: a) shor press (<s); LED is on for he acivaion ime of he key. b) long press (<s); LED is on and goes off afer seconds signalling recepion of inpu. c) double press (when acivaed); LED is on for he acivaion ime of he key (wo impulses). In he following insrucions he following symbology will be used. ( ) = shor press (s) = long press (x) = double press These symbols will be pu afer he key number examined. Keyboard Lock To block he keyboard, press key LO-DO and a he same ime (s); LED is on when he keyboard is locked. Keyboard Reacivaion To reacive he keyboard, press key LO-DO and a he same ime (s); LED is off when he keyboard is acive. Auomaic sensiiviy adjusmen Sandard se-up (deecion wih high immuniy o dus and o exeral ligh) reading disance (Fig. ) and press key ( ); key (x); LED illuminaes signalling he Fig. Diffuse Place he deecable objec a he required LED illuminaes signalling he self each operaion is in progress. Through beam Place he deecable objec beween emier and of he hrough beam as shown in (Fig. ) press key ( ); LED illuminaes signalling he self each operaion is in progress. Fine se-up (precise deecion of small objecs or deecion of ransparen objecs). Fig. Diffuse Place he deecable objec a he required reading disance (Fig. ) and press se-up complee. Fig. Fig. Through beam Place emier and of he hrough beam as in (Fig. ) press key (x). LED illuminaes signalling he se-up complee. To se he hrough beam, see paragraph alignmen help. Manual sensiiviy adjusmen Afer execuing hreshold se-up, i is possible o manually adjus he sensiiviy funcion in he following way: press key LO-DO ( ) o obain an increase in sensiiviy. The number of impulses corresponds o an equal number of sensiiviy increases. Press key ( ) o obain a decrease in sensiiviy. The number of impulses corresponds o an equal number of sensiiviy decreases. N.B. In diffuse reflecion configuraion he maximum sensing disance is obained when you press he key ( ) wihou a. Alignmen help The is se for alignmen help when you press key se (s); LED blinks wih hree differen speeds depending on he inensiy of signal received. For fine se-up applicaions, operae he alignmen as follows: Diffuse: adjus he disance of he deecable objec beween he limi of rapid and medium blinking of he LED. Through beam: adjus he emier and he posiion as o reach he limi of rapid and medium blinking of he LED. When he correc alignmen is obained, press key se (s); LED urns off signalling he end of alignmen help condiions. Oupu selecion / To inver he oupu sae from o and vice versa, i is sufficien o press key LO-DO (s). Timer adjusmen To acivae imer adjusmen modes press key se (s); LED sars blinking hus showing ha is ready for imer acivaion: a) press key LO-DO ( ); we obain a imer increase reaching ms wih he s impulse and reaching up o 5ms wih successive impulses; b) if we press key ( ), we obain a imer decrease a each impulse. c) press key ( ) if you wan o swich off he imer funcion; d) press key (s) in case you need o inver from on delay o off delay imer and vice versa; When you have finished he imer adjusmen, press key se (s); LED urns off signalling he conclusion of adjusmen funcion. N.B. Deecion is acive during imer adjusmen funcion. LED is on only when he imer has already been se-up. PhooElec//