Theatre Design & Technology - Oct 1972 - 30

nuisance tripouts that may occur when a power panel is
being hot patched and the new load is accidentally
patched to the dimmer before all of the old load is unpatched. A generally unrecognized fact is that the voltage-current relationship of an incandescent lamp as it is
dimmed is not linear. The relationship depends on the
temperature (and therefore the resistance) of the lamp
filament. This fact must be taken into account in the
protective system, since cutting voltage output in half
does not protect a dimmer running into twice its normal
maximum lamp load. The KAPP-1 overload circuit automatically phases back and reduces dimmer output when
output current exceeds maximum rating. Then current
gradually rises again until it trips the circuit breaker at
about 200 percent of rated load.
Dipless Fading and Pile-On
An optional circuit card allows fading between presets
without an unwanted dip in light intensity during the
fade. Another provides dipless fading plus what is commonly known as pile-on. Both can be added to existing
systems, but is is more economical to specify them initially.
To understand dipless fading, consider Fig. 1 again.
The potentiometers for dimmer 4 in presets A and Bare
both set at 10, so the lights controlled by dimmer 4
should not vary in intensity as the master fader is moved
from A to B or vice versa. Unfortunately, with the conventional circuit shown, light level does dip severely because the highest output from either preset A or B controls the dimmer (Fig. 4a).
To eliminate the dip, the sum of the A and B settings
should control the dimmer rather than the highest setting.
As an example, if A is added to B at the worst part of the

Dimmer 4 Conlrol VoIIJg~
and Apparent Light Output

a

dip shown in Fig. 4a, the result is 5+5=10 which is the
desired value. Adding at any other point would also give
10 and the desired linear relationship. Briefly, the dipless
fader card causes all dimmers to follow their own paths
independently and linearly from any A setting to any B
setting and vice versa. The card's basic circu itry is shown
in Fig. 4b.
"Pile-on" means retaining the lighting from one preset
and, in addition, fading in all the lighting from the other.
The circuit card for dipless fading with pile-on is similar to
the one for dipless fading, with the addition of two amplifier blocks and a block that tells the adder circuit when it
should add and when it should not. It takes advantage of
the fact, mentioned earlier, that the highest output from
preset A or B ordinarily controls the dimmer. All dimmers
with settings in either A or B stay on, and those with
settings in both A and B go to the higher of the two
settings. To implement pile-on, the mechanical tie on the
master fader (Fig. 1) is broken; the upper potentiometer is
left in position A and the lower one is moved to position

B.
Summary

The new dimmers are easily controlled and accurately
regulated. By use of modern solid-state circuit technology,
they provide light levels that do not vary, low light levels
that do not dip to a blackout condition, longer lamp life,
and tamper-proof and uniform curve settings.

The author acknowledges the contributions of James B. Tabor,
Hub Electric Company, Inc., to the development of the new lamp
dimmer and the contributions of William D. Allardice, Westinghouse Corporate Design Center, to the general appearance of the
dimmer and its enclosure.

b

with Dipless Fading

10 r;::::::::::::::::!:~::::::::::::;l,0
Dimmer 4 Control Voltage
and Apparent Light Output
without Dipless Fading

Input from
Preset A

5

Input from

Preset B

.ยง

~4

V DC

Supply

Dimm('r4
Actual llgJlI Qutllut
without Dipless Fading

A

Mid
Master Fad('r Position

4-Conventional dimmer control circuit shown in Fig. 1 causes light output from dimmer 4 to dip when fading from preset A to 8,. even'
though both are at maximum setting (a). The dip can be prevented, as shown by the curve, by modifying the circuit With an
optional dipless-fading card (b). The card's power supply is the same one shown in Fig. 1.

30

IiiiLJ

THEATRE DESIGN AND TECHNOLOGY

OCTOBER, 1972



Table of Contents for the Digital Edition of Theatre Design & Technology - Oct 1972

Contents
Theatre Design & Technology - Oct 1972 - 1
Theatre Design & Technology - Oct 1972 - 2
Theatre Design & Technology - Oct 1972 - 3
Theatre Design & Technology - Oct 1972 - Contents
Theatre Design & Technology - Oct 1972 - 5
Theatre Design & Technology - Oct 1972 - 6
Theatre Design & Technology - Oct 1972 - 7
Theatre Design & Technology - Oct 1972 - 8
Theatre Design & Technology - Oct 1972 - 9
Theatre Design & Technology - Oct 1972 - 10
Theatre Design & Technology - Oct 1972 - 11
Theatre Design & Technology - Oct 1972 - 12
Theatre Design & Technology - Oct 1972 - 13
Theatre Design & Technology - Oct 1972 - 14
Theatre Design & Technology - Oct 1972 - 15
Theatre Design & Technology - Oct 1972 - 16
Theatre Design & Technology - Oct 1972 - 17
Theatre Design & Technology - Oct 1972 - 18
Theatre Design & Technology - Oct 1972 - 19
Theatre Design & Technology - Oct 1972 - 20
Theatre Design & Technology - Oct 1972 - 21
Theatre Design & Technology - Oct 1972 - 22
Theatre Design & Technology - Oct 1972 - 23
Theatre Design & Technology - Oct 1972 - 24
Theatre Design & Technology - Oct 1972 - 25
Theatre Design & Technology - Oct 1972 - 26
Theatre Design & Technology - Oct 1972 - 27
Theatre Design & Technology - Oct 1972 - 28
Theatre Design & Technology - Oct 1972 - 29
Theatre Design & Technology - Oct 1972 - 30
Theatre Design & Technology - Oct 1972 - 31
Theatre Design & Technology - Oct 1972 - 32
Theatre Design & Technology - Oct 1972 - 33
Theatre Design & Technology - Oct 1972 - 34
Theatre Design & Technology - Oct 1972 - 35
Theatre Design & Technology - Oct 1972 - 36
Theatre Design & Technology - Oct 1972 - 37
Theatre Design & Technology - Oct 1972 - 38
Theatre Design & Technology - Oct 1972 - 39
Theatre Design & Technology - Oct 1972 - 40
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