U.S. patent number 3,597,652 [Application Number 04/790,984] was granted by the patent office on 1971-08-03 for apparatus for maintaining the temperature and operating a calibrated lamp in a constant resistance mode.
This patent grant is currently assigned to EG&G, Inc.. Invention is credited to Percival T. Gates, Jr..
United States Patent |
3,597,652 |
Gates, Jr. |
August 3, 1971 |
APPARATUS FOR MAINTAINING THE TEMPERATURE AND OPERATING A
CALIBRATED LAMP IN A CONSTANT RESISTANCE MODE
Abstract
The resistance of an incandescent lamp filament, subject to
ambient variations, is determined by sensing the current and
voltage of the lamp filament. Since the resistance is a known
function of the temperature of the filament, changes in the
temperature of the filament are sensed to provide an output
correction signal to a power supply which adjusts the input
parameters of the lamp to maintain filament temperature
constant.
Inventors: |
Gates, Jr.; Percival T.
(Weston, MA) |
Assignee: |
EG&G, Inc. (Bedford,
MA)
|
Family
ID: |
25152320 |
Appl.
No.: |
04/790,984 |
Filed: |
January 14, 1969 |
Current U.S.
Class: |
315/205; 315/257;
315/293; 315/311; 307/651; 327/190 |
Current CPC
Class: |
H05B
39/044 (20130101); G05D 23/2401 (20130101); G05D
23/2456 (20130101); Y02B 20/00 (20130101); Y02B
20/146 (20130101) |
Current International
Class: |
H05B
39/04 (20060101); G05D 23/20 (20060101); G05D
23/24 (20060101); H05B 39/00 (20060101); H05b
041/16 (); H05b 041/24 () |
Field of
Search: |
;307/282,296,297
;315/50,57,70,86,116,194,279,282,255,257,287,291,293,297,306,308,311
;328/8 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Huckert; John W.
Assistant Examiner: James; Andrew J.
Claims
What I claim is:
1. Apparatus for maintaining the temperature of a lamp filament
constant, comprising:
a source of potential connected to the filament for providing
operating parameters of a given ratio thereto;
a plurality of sensing means connected in series and in parallel
with the filament;
each sensing means detecting an operating parameter of the
filament, and each deriving respective signal voltages therefrom
representative of the sensed parameter;
means connecting the respective signal voltages to detecting means
for sensing and for deriving an error signal in response to changes
in the ratio of sensed parameters; and
means connecting the error signal to the source of potential to
vary the operating parameters and maintain the ratio constant.
2. The apparatus of claim 1, wherein:
the potential connected to the lamp filament is direct current;
and
the operating parameters are filament voltage and filament
current.
3. The apparatus of claim 2, wherein;
the means sensing the voltage operating parameter and the means
sensing the current operating parameter are a pair of magnetic
amplifier control windings; and
output windings coupled to the control windings for generating a
signal voltage representative of changes in the ratio of the sensed
voltage and sensed current of the lamp filament.
4. The apparatus of claim 3, further comprising:
a constant current power supply providing the voltage and current
parameters; and
a series passing stage in series with the power supply output for
detecting the changes in the ratio of sensed voltage to sensed
current.
5. The apparatus of claim 1, wherein:
the potential connected to the lamp filament is alternating
current; and
the operating parameters are filament voltage and filament
current.
6. The apparatus of claim 5, wherein:
the means sensing the voltage operating parameter and the means
sensing the current operating parameter are a pair of
electromagnetically coupled transformer windings; and
an output winding coupled to the pair of windings for generating a
signal voltage representative of the ratio of the sensed voltage to
the sensed current of the lamp filament.
7. The apparatus of claim 6, further comprising:
a variable output autotransformer, the input of which is connected
to the source of alternating current the output of which is
connected to one pair of windings; and
drive means connected to the output of the autotransformer for
varying the operating parameters to the transformer.
8. THe apparatus of claim 7, further comprising:
a phase sensitive detector connected to the output winding:
a source of reference phase voltage connected to the phase
detector;
the phase detector combining the signal voltage and the reference
phase voltage to derive an error signal responsive to the change in
the ratio of sensed parameters; and
means connecting the output of the phase sensitive detector to the
drive means to vary the operating parameters of the lamp filament.
Description
BACKGROUND OF THE INVENTION
This invention relates to regulating systems and more particularly
to a system for maintaining the filament temperature of a
calibrated light source at a predetermined, constant value.
When standard incandescent lamps are calibrated by the National
Bureau of Standards the Bureau provides the user of the lamps with
a sheet of instructions and procedures detailing the conditions
under which the lamp is to be operated, and typically may include a
tabulation of the calibrated light output for various filament
currents. In some instances values of spectral irradiance are
tabulated as a function of wavelength at a distance of 50
centimeters, as measured from the center of the lamp to the
receiver for a lamp current of 8.30 amperes.
The instructions cover the use of the particular filament lamp
issued as standards of spectral irradiance for a particular
wavelength range. The spectral irradiance from the lamp is based on
the spectral radiance of blackbody as defined by Planck's equation
and has been determined through comparison of a group of similar
lamps with (1) the NBS standards of spectral radiance, (2) the NBS
standards of luminous intensity, and (3) the NBS standards of total
irradiance.
THe instructions provided are quite explicit and require that the
lamp be mounted in a specific orientation in the supplied holder
which is constructed in such a manner as to reflect a negligible
amount of radiated flux in the direction of the receiver or
spectrometer slit. A black shield must be placed at a distance of
about 4 feet to the rear of the lamp to intercept stray radiant
flux along the radiometric axis and adequate shielding must be
provided to intercept stray flux from other directions. These
procedures are intended to improve subsequent user reproducibility
of calibrated output.
However, the lamp may be subject to environmental changes which
influence such reproducibility. For example, variations in
temperature of the atmosphere immediately surrounding the lamp
envelope, or unpredictable minor movements of air will tend to
produce a measurable and undesirable change in output of the
lamp.
It is well known that when a lamp is being operated, a condition of
overall thermal equilibrium is established. Both the filament and
the envelope achieve such conditions wherein power input is equal
to power output and the equilibrium is manifested in stable
temperatures at any point of both elements.
In the filament, the electrical power is converted to thermal power
causing filament temperature to increase until output power
(radiated, convected, and conducted) is equal to input power. The
envelope is heated primarily through radiation from the
filament.
A condition of thermal equilibrium of the envelope is achieved when
the power received is balanced by the power transferred to the
surroundings, such condition is again manifested by stable
temperatures.
If now more convective power is transferred to the surroundings by
the envelope (for example, by moving air or reduced ambient
temperature), envelope temperature will decrease, and by the laws
of radiation power transfer, more power will flow from filament to
envelope. Under conditions of constant filament voltage or constant
filament current, the resulting effect is reduced filament
temperature. Since the optical output power is a function of the
absolute temperature of the filament, any reduction in filament
temperature produces a corresponding reduction of light output
representing a departure from the calibrated condition.
It can be proven that a blackbody operating at 3000.degree. K. must
have its temperature maintained to an accuracy of .+-.1/4.degree.
K. to maintain the spectral irradiance to .+-.0.1 percent at 400
nanometers. This corresponds to about .+-.0.01 percent of the
resistance of a tungsten filament. It will therefore be obvious
that to maintain a constant and repeatable light output, that the
filament temperature must be held constant.
The electrical resistance of a filament is a well established
function of its absolute temperature. Thus, a given filament
temperature corresponds to a predictable and stable value of
filament resistance. Therefore, reproducibility of light output is
assured through operation at constant filament temperature which
may be achieved by such electrical input adjustment as to maintain
filament resistance constant.
It is well known that the resistance of a device is described by
Ohms' law, namely: R=E/I and that the resistance R is equal to the
ratio of voltage-to-current used by the device. Therefore, one may
determine filament resistance (R) through sensing filament voltage
(E) and current (I).
It is, therefore, one object of the present invention to provide
means for controlling the power emitted from a resistive impedance
element by utilizing the relationship between the resistance of the
element and the total emissive power therefrom.
Another object of the present invention is to provide a control
circuit for controlling a standard, calibrated lamp utilizing the
relationship between the total emissive power or lamp brightness
and the lamp filament resistance.
Still another object of the present invention is to provide a
control system for detecting subtle changes in resistive impedance
of a calibrated lamp due to changes in surrounding conditions.
Yet another object of the present invention is to provide a control
system for a standard calibrated lamp capable of detecting changes
in ambient conditions in the vicinity of the lamp by detecting
changes in the ratio of voltage-to-current (E/I ) or resistance of
the filament.
The features of my invention which I believe to be novel are set
forth with particularlity in the appended claims. My invention
itself, however, both as to its organization and method of
operation, together with further objects and advantages thereof,
may best be understood by reference to the following description
taken in conjunction with the accompanying drawing.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plot of current and voltage across the terminals of an
incandescent, light standard;
FIG. 2 is a block diagram incorporating the features of my
invention wherein a constant ratio of voltage to current is
maintained in a calibrated lamp system;
FIG. 3 is a circuit diagram of one embodiment of a system
incorporating the features of the invention for controlling the
light from a calibrated light source by maintaining a constant
ratio of voltage to current; and
FIG. 4 is a circuit diagram of another embodiment of a system
incorporating the features of the invention for controlling the
light from a calibrated light source by maintaining a constant
ratio of voltage to current.
SUMMARY OF THE INVENTION
As will be hereinafter shown, my device senses the voltage applied
to and the current passing through a high temperature resistive
impedance, such as calibrated lamp, and treats the ratio of voltage
to current sensed (E/I ) as the parameter most indicative of the
element temperature. This parameter, in the case of a lamp
filament, represents a measure of the brightness of the lamp. By
maintaining this ratio of E/I constant, in spite of variations in
the lamp environment, I am able to achieve a constancy of light
output far exceeding that resulting from the recommended method
involving constant filament current.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown a plot of current versus
voltage wherein curve A may represent the current through the
filament over a range of values of filament voltage under a set of
constant lamp environmental conditions. It may be noted that as
current (or voltage) is increased, filament resistance is increased
as is evidenced by the curvature of the characteristic curve. At an
opening point x, the filament is operating at a unique value of
resistance as shown by dashed line R. This resistance in turn
corresponds to a unique and particular filament temperature. The
present invention provides circuitry for operating a lamp filament
at the intersection of its characteristic E-I curve and line R of
constant resistance.
Referring now to FIG. 2, there is shown, in block diagram form,
power source 12.1 having leads 12.3 and 12.4 for supplying power to
series connected lamp 14. Voltage sensing means 16, connected in
parallel with lamp 14, and current sensing means 18, connected in
series with lamp 14, each is provided with an output which is
applied as an input to regulator 20.1. Regulator 20.1 produces a
signal voltage at output lead 20.2 which is representative of the
ratio of the voltage to the current (E/I ) being used by lamp 14.
This correction or error signal voltage is fed to power source 12.1
as a means for varying a parameter of lamp 14. A manual adjustment
means 12.2 is provided in power source 12.1 to initially set the
operating conditions of the power source while the error signal,
appearing on lead 20.2 is the means for making a fine adjustment to
maintain the E/I ratio or resistance of lamp 14 constant.
Referring now to FIG. 3 there is shown another embodiment employing
the principles of my invention which utilizes direct current (DC)
means for controlling the parameters of lamp 14 so that it will
maintain its proper operating conditions. The components enclosed
within dotted line 40 represent a magnetic amplifier wherein first
control winding 18, connected in series with lamp 14, represents
the current sensing means and second control winding 16.1, together
with variable resistor 16.2 is connected in parallel with lamp 14
and represents the voltage sensing means. As is well known in the
art, magnetic amplifier 40 is provided with an excitation means
20.5 having a primary winding connected to terminals 20.6 and 20.7
to which is connected a suitable source of excitation (not shown).
Center-tapped secondary 20.8 has one end thereof connected to the
series connected load windings 20.2 and 20.3 and has its other end
connected to the series load windings 20.1 and 20.4. Each of the
load windings 20.1, 20.2, 20.3 and 20.4 is connected to one end of
respective diodes 22.1, 22.2, 22.3 and 22.4. The other ends of
diodes 22.1 and 22.2 are connected to one end of load resistor 24.1
and the common junction of the diodes and resistor is connected to
output terminal 26.1. Similarly, the other ends of diodes 22.3 and
22.4 are connected to one end of load resistor 24.2 with the
junction common to these latter elements connected to output
terminal 26.2. To complete the circuit, the other ends of resistors
24.1 and 24.2 are connected together and to the center tap of
excitation winding 20.8.
In the operation of my device in this mode it will be seen that
lamp 14 is provided with the appropriate value of current and
voltage, from source 12.1. Variable resistor 12.2 is provided in
supply 12.1 for providing the initial settings of current and
voltage to maintain the proper operating conditions. If, after the
initial parameters are set, the ambient conditions change and the
lamp is now subjected to a movement of air sufficient to reduce the
temperature of the lamp envelope, the operating conditions will
change. Assume for example, that as originally set up, the lamp is
made to operate at a voltage and current that would correspond to
point x of curve A (FIG 1). If now the ambient conditions change so
that the lamp envelope temperature is lowered, the temperature of
the filament would also change as the equilibria are upset. If now
source 12.1 were a constant current source, it would be obvious
that for the current to be maintained constant the operating point
would be shifted along line y to curve B so that operation would be
at point z corresponding to a different filament resistance and
hence filament temperature. This would substantially alter the
light output of lamp 14, as there is a lower voltage appearing
across the filament of the lamp and indicating a change in filament
resistance. However, the turns ratio of control windings 16.1 and
18 together with resistance 16.2 were appropriately selected so
that any changes in sensed voltage to current ratio were manifested
by the appearance of an error signal at the output terminals 26.1
and 26.2. One may then use the error signal to maintain a constant
ratio of E/I or resistance. The windings may be arranged so that if
a positive going signal were to appear at terminals 26.1 with
respect to 26.2 it would be indicative of a lamp load condition
which indicates that the current passing through lamp 14 is too
high. A negative voltage at the terminals would indicate that the
current is too low while the amplitude of the signal would be
proportional to the error. This error signal is then applied to the
base of transistor 12.3 to regulate the current and voltage
appearing at the output terminals of DC source 12.1 and thereby
maintained the present E/I ratio so that lamp characteristic curve
B (FIG. 1) will not be operated at point w.
It is known in the art that a magnetic amplifier of this type
produces an output voltage proportional to the algebraic addition
of the ampere-turns of the central windings. In the system
configuration of FIG. 3, feedback control action tends to reduce
the net ampere turns of control windings 16.1 and 18 toward zero. A
null at output terminals 26.1 and 26.2 corresponds to a constant
ratio of the E to I of lamp 14.
Referring now to FIG. 4, there is shown another embodiment
employing the principle of my invention and which operates the lamp
in an alternating current (AC) mode. In this embodiment transformer
140, indicated within dotted line is provided with winding 118
which represents the current sensing means and winding 116.1 which,
together with resistor 116.2, represents the voltage sensing
means.
Operating potential is derived from autotransformer 136 which may
be of the type known commercially as a "Variac." A source of AC
potential (not shown) is applied to terminals 138.1 and 138.2 so
that the AC potential appearing thereacross may be picked, at any
suitable value, by moveable arm 134. This potential is then applied
through current sensing winding 118 which is in series with lamp
load 114. Transformer 140 is further provided with a center tapped
sensing winding 120 for detecting changes in the sensed current and
voltage used by lamp 114. When slight changes in the operating
parameters occur, the change will be marked by the appearance of an
AC error voltage in winding 120. The amplitude is proportional to
the degree of unbalance. The voltage will be in phase or
180.degree. out of phase with the line according to the sense of
the unbalance. The resulting error signal is then applied to a
phase sensitive detector 122.1, the output of which is a DC signal
which may have, for example, a positive value when conditions
indicate a high current through lamp 114 and the negative value for
low current through lamp 114. As in the previous embodiment, the
amplitude of the signal from detector 122.1 will be proportional to
the error. This output error signal is then applied as an input to
a drive on amplifier means 128 which, in turn, provides a signal at
its output, suitable to operate servo or motor means 130. The shaft
of servo means 130 is coupled to the moveable arm 134 of
autotransformer 136, as indicated by dotted lines 132, so that
rotation of the shaft of servo means 130 will, with the appearance
of an error signal at the output of detector 122.1, appropriately
vary the input parameters to lamp 114 and thereby reduce the error
signal to zero and hence maintain the required constant E/I
ratio.
While there has been described what is presently considered the
preferred embodiment of my invention, it would now be obvious to
all those skilled in the art that various other changes and
modifications may be made therein without departing from the
inventive concept contained herein and it is, therefore, aimed to
cover all such changes and modifications as fall within the true
spirit and scope of my invention.
* * * * *