Download lighting control by strand electric

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