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Transcript
IJ LIGHTING CONTROL BY STRAND ELECTRIC Nowhere does Strand Electric's long experience, allied to the latest technical development, show to better advantage than in modern lighting control. In these pages will be found a range unapproached in its comprehensiveness; covering as it does, preset controls for the tightest budget on the one hand and for the largest theatre or television studio on the other. This new range uses the latest form of dimmer - the thyristor - which is backed by Strand 's seven years practical experience in the field with large pilot installations. To date (summer 1966) Strand Electric has over 7000 thyristor channels installed and working . To purchase a Strand Control is to take advantage of all this know-how of ' the new' and combine it with the knowledge and experience that comes from growing up with electric stage lighting controls from their infancy. Strand designers have antiCipated each new advance whether in technology or production which explains why Strand are always first. Even more important than technical development is design from the operator's point of view. It is all too easy for engineers and designers to chase each new technical device regardless of operational desirability. Strand controls are supervised through every design stage by men who are operators themselves. Men who know what it is like to work production lighting plots with anything from four to over two hundred or more dimmer channels to control. Strand Electric with all the large theatres and television studios in Britain to their credit have not neglected the other end of the scale for example they have in one type alone, the Strand Junior 8 (4 dimmer 8 circuit) supplied over 3000 in the first 30 months after its introduction . This plus no less than 146 preset control installations in theatre and television in Britain alone, to say nothing of export, enables Strand Electric to claim to know this work from top to bottom . The most obvious features of any of the standard Strand Preset Controls described herein is their clarity of layout and fine finish . Strand Controls are not just well styled and made but have an instrumental finish gracious to the touch and smooth to operate. It is Strand Electric's large world market which enables them to tool up for precision moulding of purpose- made items such as dimmer levers. It is significant that the Strand standard lever when exported to the United States to be incorporated in the controls of a famous firm over there is described as de luxe and charged for as an extra! Basic simpl icity in the number of controls fitted means clarity in layout which in its turn spells versatility. It is all too easy to build up a complicated panel covered with levers, switch es, extra sub masters and grand masters. Such things not only take up unnecessary space but visually confuse. The operator cannot make a rapid appraisal to take in the situation at a glance. In a Strand control just those controls that are needed are supplied and care is taken to position and design them so the operator can relax and use them with confidence. Strand controls are easy to learn and no nerve racking nightmares follow in which the operator wonders if all is set properly for th e next cue. What is a Thyristor Dimmer? This is an entirely different method of dimming employing a form of transistor which Strand Electric introduced to Europe in an experimental version in 1959. There followed experimental testing with a thirty channel control in our own demonstration theatre. Like all new devices t he thyristor (then known as the SCR) was expensive to begin with; until in fact mass production got underway. During this development period special equipments were made by Strand and formed large pilot installations in various parts of Europe. Most of these were for television lighting because electronic circuitry is particularly familiar to their engineers. However two large theatre installations Glyndebourne and Covent Garden representing between them 360 dimmer channels, were also completed . Only then after all this practical experience in the field did Strand Electric consider it right to standardise on this new dimmer for general application as shown herein . Such application covers everything from small self-contained portable equipment to the largest and most complete control conceivable. Strand Thyristor dimmers can control not only the normal tungsten stage lighting and the new tungsten halogen lamps (commonly referred as quartz iodine) but also fluorescent discharge lamps. Howa Thyristor Works The thyristor is a solid state device known as a sem iconductor or rectifier, which is a relation of the transistor but used to control heavy currents at mains voltages. Strand thyristor dimmers are available in standard modules of up to 5kW on 200/250 volt* . Each dimmer has a pair of thyristors used in the manner known to engi neers as back to back. As is generally known, electric supply alternates above (positive) and below (negative) zero making a complete cycle fifty times every second . This cycle when averaged out gives the full mains voltage for which lamps and either electrical equipment are designed. When a pair ofthyristors (Le. semi-conductors) is inserted back to back in the circuit one of them conducts for the positive half cycle and the other for the negative half and the result adds together as full mains voltage once more. However the thyristor is what is known as a controlled rectifier and regulation can be applied to the pair from a small dimmer lever in such a way that each passes less and less of its half cycle. In consequence the voltage averages at less and less until stopped off compl etely. It follows that any lamps fed can be given their full voltage or starved of it until they are extinguished . Unlike the resistance dimmer and saturable reactor (choke) dimmers commonly used in Britain the thyristor is not load dependent. For example if set to pass only that part of the AC cycle which represents half light (80 % full volts) then it will make no difference withi n the stated top capacity of the dimmer how many or how few lam pst are switched into the circuit, each will be at half light. The control voltages and current at the dimmer lever are very small indeed and there are no moving parts to the thyristor dimmer itself. One precaution however must not be overlooked, though it usually is by firms anxious to jump on the thyristor band-wagon, and that is the need for what is known as 'clean-up.' The electrical effect of chopping the waveform , especially in the dim positions below half light, is to create a pulsing current which may radiate electrical interference to be picked by the theatre' s sound amplifiers and which may cause actual noise at the lamp filaments. This can, however, be corrected by an iron-cored filter in series with the load. The degree of clean - up necessary varies and all Strand thyristor control systems are designed to take this into account, also Strand thyristor racks are available in two main forms; the Junior J.T.M. type and Senior T.M. All control desks can operate in conjunction with either or both simultaneously. *A similar rang e but 6 kW is avail abl e for 100/120 Volts, 60 cycles. All thyristor dimm ers req ui re t o be load ed to not le ss than 60 watt s t o co ntrol properly. t l