U.S. patent number 3,742,188 [Application Number 05/247,062] was granted by the patent office on 1973-06-26 for dummy load system.
This patent grant is currently assigned to Continental Electronics Manufacturing Company. Invention is credited to Earl W. Sundbye.
United States Patent |
3,742,188 |
Sundbye |
June 26, 1973 |
DUMMY LOAD SYSTEM
Abstract
A dummy load includes a resistive sodium nitrite resistive load
directed by insulating tubes to flow in the load. The cooling
circuit includes a primary circuit having inlet and outlet
thermistors, and a secondary cooling circuit coupled thereto by a
liquid to liquid heat exchanger. In the control circuit, the
thermistors are serially connected in a bridge circuit, unbalances
in the bridge being detected to directly control a motor for
controlling a valve in series in the secondary loop. A pair of
slower moving valves in series and shunt respectively in the
secondary loop are controlled upon the movement of the directly
controlled valve to a limit position.
Inventors: |
Sundbye; Earl W. (Garland,
TX) |
Assignee: |
Continental Electronics
Manufacturing Company (Dallas, TX)
|
Family
ID: |
22933397 |
Appl.
No.: |
05/247,062 |
Filed: |
April 24, 1972 |
Current U.S.
Class: |
338/56; 165/164;
392/465; 165/108 |
Current CPC
Class: |
H01P
1/262 (20130101) |
Current International
Class: |
H01P
1/26 (20060101); H01P 1/24 (20060101); F24h
001/20 () |
Field of
Search: |
;219/323,325,330,314,316
;338/56 ;165/108,164,180,181 ;333/22F,22R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Albritton; C. L.
Claims
What is claimed is:
1. A dummy load system comprising a primary liquid circulation loop
for circulating a resistive liquid coolant, a dummy load having a
circulating channel connected in said first loop whereby said
liquid in said channel forms a resistive load in said dummy load, a
secondary liquid circulation loop, a liquid to liquid heat
exchanger intercoupling said primary and secondary loops, motor
controlled valve means connected in said secondary loop for the
control of liquid flow therein, first and second thermistors
thermally coupled to said first loop at the input and output of
said channel, a bridge circuit, said first and second thermistors
being serially connected in one arm of said bridge circuit, and
means responsive to the balance of said bridge circuit for
controlling said motor controlled valve means whereby the mean
temperature of said liquid in said channel is maintained
substantially constant.
2. The dummy load system of claim 1 wherein said motor controlled
valve means comprises first and second motor controlled valves in
series in said secondary loop, a third motor controlled valve in
shunt in said secondary loop, said means responsive to the balance
of said bridge circuit being connected to directly control said
first motor controlled valve, said first motor controlled valve
having limit switch means, and means responsive to the operation of
said limit switch means at predetermined positions of said first
valve for deenergizing said first valve means and energizing said
second valve means to operate in the same respective direction and
to energize said third valve means to operate in the opposite
relative direction.
3. The dummy load system of claim 2 wherein said second and third
valves operate at a predetermined lower speed than said first valve
when energized.
4. The dummy load system of claim 1 further comprising resistance
heater means coupled to heat the liquid in said primary loop, and
thermal switch means thermally coupled to said first loop and
connected to energize said resistance heater means.
5. The dummy load system of claim 4 wherein said means for
controlling said motor control valve means comprises means for
energizing said resistance heater means in response to the
detection of mean liquid coolant temperatures below a predetermined
level in said channel coolant.
6. The dummy load system of claim 1 wherein said motor control
valve means comprises a first motor controlled valve serially
connected in said secondary loop, said means for controlling said
motor control valve means comprising means for directly controlling
said first motor control valve, said first motor control valve
having limit switch means for inhibiting further energization
thereof at predetermined positions thereof, a second motor control
valve serially connected in said secondary loop and connected for
energization in the same respective direction to said first motor
control valve means by means of said limit switch means, and a
third motor control valve connected in shunt in said secondary loop
and connected for energization to said limit switch means upon
operation thereof, in the opposite respective direction to said
first motor control valve.
7. The dummy load system of claim 6 further comprising resistive
heater means coupled to said primary loop, said means for
controlling said motor control valve means including means for
energizing said heater means in response to the detection of
predetermined low temperature of said liquid coolant.
8. The dummy load system of claim 6 further comprising manual
switch means for selectively energizing said first, second and
third motor control valves.
9. The dummy load system of claim 6 further comprising
over-temperature switch means coupled to said primary loop,
solenoid control valve means in said secondary loop bypassing said
first and second motor control valve, and means for energizing said
solenoid control valve means from said over-temperature switch
means in response to predetermined temperature of said liquid
coolant in said primary loop.
10. The dummy load system of claim 6 wherein said means for
controlling said motor control valve means comprises optical meter
relay means.
11. The dummy load system of claim 1 wherein said dummy load is
comprised of an outer insulating tube coupled to said primary loop,
an inner insulating tube coaxial with said outer tube and connected
to said primary loop, a conductive transition member sealed to the
end of said outer tube for connection to the central conductor of a
transmission line, whereby said liquid coolant circulates in one
direction in said inner tube and the opposite direction between
said outer and inner tubes and around the end of said inner tube
between said inner tube and transition member.
12. The dummy load system of claim 11 wherein said dummy load has
an outer sheath in the shape of a tractorial curve in the region
thereof surrounding said inner and outer tubes, said outer sheath
tapering toward said tubes at the bottom of said dummy load and
forming thereat a short circuit for RF currents.
13. In a dummy load system of the type including a dummy load
having a resistive liquid coolant serving as a load, and a
circulating path therein for said coolant, and wherein said system
further comprises a circulating loop for circulating said coolant
through said path, first and second thermistors thermally coupled
to the loop at the inlet and outlet of the path, motor driven valve
means for controlling the temperature of said liquid in the
circulating loop, and means responsive to the resistance of said
thermistors for controlling said motor driven valve means; the
improvement wherein said means responsive to the resistance of said
thermistors comprises a bridge circuit, said thermistors being
connected in series in one arm of said bridge circuit, and means
responsive to the balance of said bridge circuit for controlling
said motor driven valve means, whereby said valve means controls
the temperature of said liquid coolant to maintain the mean
temperature thereof in said path substantially constant.
14. The dummy load system of claim 13 further comprising a
secondary liquid circulating loop, liquid to liquid heat exchanger
means intercoupling said second and first mentioned circulating
loops, and wherein said motor driven valve means comprises first
valve means serially connected in said secondary loop and connected
to be directly driven by said means for controlling said motor
driven valve means, limit switch means on said first motor driven
valve means, a second motor driven valve means connected serially
in said secondary loop for energization in the same respective
direction as said first motor driven valve means upon operation of
said limit switch means at predetermined positions of said first
valve means, and a third motor driven valve means connected in
shunt in said secondary loop for energization upon operation of
said limit switch means and in the opposite respective direction to
said first motor driven valve means.
15. The dummy load system of claim 14 further comprising resistive
heater means coupled to said first mentioned loop for heating the
liquid therein, and wherein said means for controlling said motor
driven valve means comprises means for energization of said
resistive heater means in response to the detection of a mean
temperature below a given value in said circulating path.
Description
This invention relates to arrangements for the dissipation of radio
frequency power, and is more particularly directed to an improved
dummy load of the type adapted to be connected to an RF
transmission line for dissipation of power, and a system for
maintaining the temperature of a liquid resistive coolant in the
dummy load and determining the dissipated power. Such maintenance
of temperature is necessary in order to maintain desired VSWR
characteristics, in view of the variation of resistance of the
resistive coolant with temperature.
In the past, dummy load devices have been provided of the type in
which the central conductor terminates in a broad band resistive
element comprised of a pair of coaxial insulating tubes through
which a suitable material such as sodium nitrite is adapted to
flow. Such arrangements are provided with outer shields connected
to the transition lines surrounding the resistive element, the end
of the shield tapering inwardly toward the end of the dummy load
and terminating with an RF short to the resistive element.
In the cooling circuit for such a dummy load device, the sodium
nitrite has been circulated in a loop which may consist of a
reservoir of sodium nitrite, and a heat exchanger. Thermistors are
individually coupled to the input and output lines of the dummy
load device to provide an indication of the temperature of sodium
nitrite, and these thermistors were connected to an automatic
control system for maintaining the temperature of the coolant at a
mean given value, for example, by controlling the flow of fluid by
means of a motor driven valve at the input of the heat exchanger
from a source of raw water.
It is an object of the present invention to provide improvements in
such dummy load systems, by maintaining improved control over the
temperatue of the liquid coolant over wider ranges of power inputs,
as well as to simplify the control system, and improve the VSWR
characteristics, thereby providing a system having broad band
characteristics over an extremely large frequency and power
range.
According to the invention, a dummy load for absorbing RF power
received by way of a transmission line, is comprised of a resistive
central conductor surrounded by a conductive sheath. The central
resistive element is comprised of a pair of coaxial insulating
tubes arranged so that a flow of coolant, such as sodium nitrite,
may be passed in one direction through the inner insulating tube,
around the ends of the inner tube at the junction of the resistive
element with a transition piece to the central conductor of a
transmission line, and thence in the opposite direction between the
outer and inner tubes. The conductor transition piece is shaped to
maintain nominal impedance and to have anti-corona and high
frequency characteristics. The outer sheath has a smooth transition
to the outer conductor of the transmission line, and follows a
tractorial curve throughout the resistive portion of the dummy
load, thereby tapering inwardly to the resistive element at the end
of the dummy load to provide an RF short at its termination. The
curves of the outer sheath are shaped to maintain the nominal
impedance in the transition to the standard transmission line. With
this arrangement, the dummy load has characteristics that are
extremely flat up to at least 100 megacycles, and the device does
not have to be derated in the high frequency range.
The cooling system for the liquid coolant is comprised of a primary
cooling loop connected to the dummy load for circulating the
coolant therethrough, and a secondary loop for circulating another
liquid, such as water, and coupled to the primary loop by a liquid
to liquid heat exchanger. Three control valves are provided in the
secondary loop for controlling the flow therethrough, and thereby
to control the temperature of the liquid coolant. The valves are
motor controlled, two of which are in series in the secondary
circuit, and the third of which is in parallel in the secondary
loop circuit. A pair of thermistors are coupled to the primary
loop, at the input and output of the dummy load, and these
thermistors are connected in series in one arm of a bridge circuit.
A control circuit, responsive to unbalance of the bridge circuit,
directly controls the motor coupled to one of the series valves in
the secondary loop. The other two motors are controlled by means of
back contacts on limit switches of the first motor valve
arrangement, and extend the range of control over the liquid flow
in the secondary loop, the series valve being controlled in the
same direction as the primarily controlled motor, with the shunt
valve being controlled in the opposite direction. The coupling
between the output of the bridge circuit and the control for the
motors may be in the form of an optical meter relay.
Since the thermistors coupled to the primary loop are in series in
the bridge circuit, the control system serves to control the
temperature of the fluid at the mean value of temperature as
indicated by thermistors. This arrangement provides a simple and
inexpensive control over the temperature.
In addition, the primary loop may include heating means, for
example in a reservoir, responsive to a thermal switch, for
preheating of the liquid coolant, in order to obviate the necessity
for warmup periods for the system, which previously had
necessitated low power gradual warmup prior to use of the dummy
load as desired.
The invention will now be disclosed in greater detail with
reference to the accompanying drawings, in which:
FIG. 1 is a simplified schematic diagram of a system for
controlling the temperature of a dummy load according to one
embodiment of the invention, and illustrating a typical dummy load
that may be employed in combination therewith partially in cross
section;
FIG. 2 is a simplified circuit diagram of a circuit that may be
employed for controlling the system of FIG. 1;
FIG. 3 is a schematic diagram of a more complete system for
controlling the temperature of a dummy load, according to the
invention, this embodiment illustrating the system for controlling
the temperature of a pair of dummy load devices;
FIG. 4 is a simplified circuit diagram of a modification of a
portion of the circuit of FIG. 2, the arrangement of FIG. 4 being
particularly adapted for incorporation in the system of FIG. 3;
and
FIG. 5 is a simplified circuit diagram of a portion of a control
circuit which may be incorporated in the systems of FIGS. 1 and
3.
Referring now to FIG. 1, therein is illustrated a dummy load 10
adapted to absorb the radio frequency power from a transmission
line 11. The central conductor 12 of the transmission line is
connected to the resistive portion 13 of the dummy load by way of a
conductive transition member 14 having a smooth transition. The
resistive portion of the dummy load is comprised of an outer
insulating tube 15 sealingly joined at one end to the end of the
transition piece 14 and extending axially through the dummy load
and terminating in an outlet 16. An inner insulating tube 17, also
for example of glass of plastic, is provided within the outer tube
15 and extending coaxially therewith. One end of the inner tube 17
is spaced from the transition piece 14, and the other end extends
to an inlet 18 for providing fluid coolant to the structure. The
tubes are arranged to that the liquid coolant flows from the inlet
18 upwardly through the tube 17, and thence downwardly between the
inner and outer tubes to the outlet 16. The end of the transition
piece 14 may be shaped to provide a smooth flow for the fluid at
the upper end of the inner tube 17.
The outer conductor 20 of the transmission line is connected to the
outer conductive shield 21 of the dummy load. The outer shield
extends downwardly from the outer conductor 20 with a smooth
transition to an enlarged diameter region at the upper end of the
resistive portion of the dummy load, and thence tapers downwardly
and inwardly to the outer surface of the outer tube 15 at the
bottom of the device. The curve of the outer shell 21 is preferably
in the form of a tractrix in the portion thereof surrounding the
resistive portion of the dummy load. The upper portion of the outer
shield 21 is shaped to maintain the nominal impedance in the
transition region to the transmission line, and the inner
transition member 14 is also shaped to maintain the nominal
impedance, as well as to provide the desired anti-corona and high
frequency characteristics.
The cooling system in the arrangement of FIG. 1 includes a primary
loop 30 adapted to circulate a suitable resistive coolant such as
sodium nitrite through the tube 15 and 17 of the dummy load, and a
secondary loop 31 coupled to the loop 30 by way of a liquid to
liquid heat exchanger 32 for circulating a coolant such as water to
remove heat from the primary loop.
As illustrated in FIG. 1, the primary loop 30 includes a liquid
reservoir 35. A suitable pump 36 draws sodium nitrite solution from
the reservoir 35 and passes it through the heat exhanger 32, and
thence into the inlet 18 of the dummy load. The outlet 16 of the
dummy load is connected to return the fluid to the reservoir 35. A
thermistor 37 is coupled to the fluid path at the inlet 18 of the
dummy load, and a second thermistor 38 is coupled to the fluid path
at the outlet 16 of the dummy load. The thermistors 37 and 38 are
employed to control the temperature of the fluid in a manner that
will be discussed in more detail in the following paragraphs. The
system also includes a temperature responsive switch 40 of
conventional nature arranged in thermal contact with the liquid in
the reservoir 35, the switch 40 being serially connected with a
suitable electric heater 41 disposed in a position to heat the
liquid in the reservoir 35 by means of a suitable source 42, as
will be discussed in more detail in the following paragraphs.
The secondary cooling loop 31 is adapted to circulate a suitable
coolant, such as water, from an external heat exhanger 45 through
the heat exhanger 32 by way of motor controlled valves 46 and 47,
these valves being controlled by suitable means from the shafts of
motors 48 and 49 respectively. An additional motor controlled valve
50, controlled by motor 51, is connected between the inlet and
outlet of the heat exchanger 45, and, if necessary, pumping means
such as pump 52 may be provided to circulate fluid in the secondary
loop 31. The source of fluid and pumping arrangement for the
secondary loop as illustrated in FIG. 1 is exemplary only, and it
will be apparent that other techniques may be employed for
circulating this fluid in the secondary loop.
Referring now to FIG. 2, a control circuit for the system of FIG. 1
is comprised of a bridge circuit 60, the resistive elements of the
thermistors 37 and 38 of FIG. 1 being serially connected in one arm
of this bridge circuit. Suitable resistance elements 61, 62 and 63
are provided in other arms of the bridge circuit, preferably at
least one of these other elements being variable to permit
adjustment and calibration of the bridge circuit. A suitable
voltage source 64 is connected to the source terminals of the
bridge circuit, for example by way of a variable calibration
resistor 65, and the output diagonals of the bridge circuit are
connected to the input of a bridge detector circuit 70. The bridge
detector detects unbalances in the bridge circuit resulting from
variation in the resistance of the thermistors, and actuates a
relay control circuit 71 for controlling the valve control motors
48, 49 and 51. The bridge detector circuit 70 and relay control
circuit 71 may be of any conventional nature, and in one suitable
embodiment of these devices an optical meter relay has been
employed for the control circuit. FIG. 2 illustrates a switch 72 in
the relay control circuit 71 to show the operational function of
the control circuit. Thus, the switch serves to connect an input
power lead 73 selectively to output control leads 74 or 75 if the
bridge is unbalanced, the connection being determined by the sense
of the unbalance. As noted above, this representation of the
control of the circuit 71 is functional only, and it is apparent
that any conventional technique for achieving this function, in
dependence upon the bridge unbalance, may be suitably employed in
the circuit of FIG. 2.
Still referring to FIG. 2, the circuit further includes a
manual-automatic switch 80, having contacts 81, 82, 83, 84, 85 and
86. This switch is shown in the "automatic" position, in which the
valve control motors 48, 49 and 51 are automatically controlled in
response to the variation of resistance of the thermistors 37 and
38 in a determined manner. In the "manual" position of the switch
80, the valve control motors 48, 49 and 51 may be selectively
manually controlled by means of switches 87, 88 and 89
respectively, as will be explained in more detail in the following
paragraphs.
The valve control motor 48 is a reversible motor of conventional
type, such as a split phase motor for operation from single phase
current as illustrated. Suitable limit switches 90 and 91, operable
at the respective opposite extremities of the desired control range
of the valve 46, serve to connect the opposite ends of the windings
of the motor 48 to the leads 74 and 75, as illustrated in the
figure, when the switches 90 and 91 are off their limits. The
common lead 92 is connected to a reference potential. Similarly,
the valve control motor 49 is coupled to limit switches 93 and 94
operable at opposite extremities of the control range of the valve
47, and valve control motor 51 is coupled to limit switches 95 and
96 operable at opposite extremities of the range of the valve 50.
The common leads of the motors 49 and 51 are also connected to
reference potential.
The normally not connected contacts of limit switch 90 are
connected by way of switch 84 and limit switch 93 to one lead of
the motor 49, and by way of contacts 83 and limit switch 96 to one
lead of the motor 51. Similarly, the normally non-connected
contacts of limit switch 91 are connected by way of switch 86 and
limit switch 94 to the other operating lead of motor 49, and by way
of contacts 85 and limit switch 95 to the other operating lead of
the motor 51.
Power for operating the motors is derived from terminals 98 at a
suitable source of electric power, and applied to the arm of the
switch 82, and thence, in the "automatic" position, to the lead 73
so that the control circuit 71 determines the operation of the
motors. In the manual position of the switch 82, the power source
is connected to the arms of the switches 87, 88 and 89. The
switches 87, 88 and 89 are of the type having a central unconnected
position, so that they may be manually controlled to apply power to
either one of the fixed contacts. The fixed contacts of the switch
87 are connected to the leads 74 and 75 for operation of the motor
48. Similarly, the fixed contacts of switch 88 are connected to
opposite leads from the motor 49, and the fixed contacts of switch
89 are connected to opposite leads of the motor 51, for selective
operation of these motors.
The manual-automatic switch 80 of FIG. 2 also includes contacts 81
having the fixed contact in the automatic position connected to the
lead 74, and the fixed contact in the manual position connected to
the source terminal 98. The arm of the switch 81 is connected by
way of thermally operated switch 40 to a relay coil 99 having
contacts 100 connected to apply power from a suitable source 101 to
the resistive heater 41. As seen in FIG. 1, the thermal switch 40
and the heater 41 are disposed on or in the reservoir 35.
In operation of the arrangement of FIG. 2, it is apparent that, in
the automatic position of the switch 80, the relay control circuit
71 controls the motor 48, and hence the valve 46, and that the
motors 49 and 51 will not be energized as long as the limit
switches 90 and 91 of the motor 48 have not been operated. As seen
in FIG. 1, the valve 46 is in series in the secondary loop 31, so
that the relay control circuit 71 directly controls this valve by
way of the motor 48, in response to variation in resistance of the
thermistors 37 and 38. For example, if the mean temperature of the
dummy load fluid is too low, as indicated by the resistance values
of the thermistors, the relay control applies power to the lead 74,
and thence by way of limit switch 90 to the motor 48, to operate
the valve 46 in the closing direction. Simultaneously, the power is
applied by way of the lead 74, contact 81 of switch 80, and thermal
switch 40 to energize the relay 99, thereby applying heat to the
fluid in the reservoir by means of the heater 41. The heater 41 and
thermal switch 40 provide means whereby the liquid in the first
loop may be heated prior to operation of the dummy load, and
thereby obviating the necessity for operating the RF source
connected to the dummy load at a lower power during a warmup
period, as was the previous practice. The system of FIG. 2 thereby
prepares the cooling circuit for proper operation without the
warmup period being required. If, during the closing of the valve
46, the limit switch 90 is operated, the limit switch then applies
the operating power to windings of the motors 49 and 51 by way of
switch contacts 84 and 83 respectively. The motor 49 operates the
valve 47 in the same sense as the valve 46, since the valve 47 is
also in series in the second loop, while the valve 50 will be
operated in the opposite sense, i.e., to open this valve when the
temperature is low, since this valve is in parallel in the second
loop. The motors 49 and 51 are preferably arranged to operate at a
lower speed, for example, at one fourth the speed, with respect to
the motor 48, and these valves are arranged to vary the fluid flow
in the second loop in predetermined limited amounts, so that the
three valves 46, 47 and 50 permit the system to automatically
handle widely varying power levels without the necessity of any
adjustments. In the above examples, the limit switch 94 of motor 49
limits the control of the valve 47 in the opening direction, while
the limit switch 95 of the motor 51 limits the control of the valve
50 in the closing direction.
When the bridge detector 70 indicates that the temperature to be
controlled is too high, the relay control energizes the lead 75, to
effect the control of the motor 48 in the opposite direction, and
in the similar fashion, to control the motors 49 and 51 in the
opposite direction when the limit switch 91 is operated. In this
case, of course, no additional heat is applied to the fluid in the
first loop 30 by the heater 41.
As noted above, the thermistors 37 and 38 are connected in series
in one arm of the bridge circuit, and as a result of this
connection, the system controls the temperature of the fluid in the
first loop so that the mean temperature in the dummy load is
maintained substantially constant. Thus, when radio frequency power
is applied to the dummy load, the outlet temperature increases, and
the cooling system controls the fluid temperature, by controlling
the valve, to permit the inlet temperature to drop, thereby keeping
the mean temperature at substantially a constant value. For
example, except in extremely hot environments, the mean temperature
may be set to approximately 70.degree.C. By the use of the three
motor driven valves in the secondary loop, which controls the
secondary loop flow through the liquid to liquid heat exchanger 32,
it has been found that the VSWR of the dummy load may be maintained
within 1.2:1.
FIG. 3 illustrates a more complete system in accordance with the
invention, as it may be employed in an actual embodiment for the
control of the sodium nitrite coolant of a pair of dummy loads 110
and 111. These dummy load devices may be of the same form as that
illustrated in FIG. 1. In the arrangement of FIG. 3, the cooling
channels of the dummy load are connected in parallel in the primary
cooling circuit 30. The primary circuit, in addition to the
elements disclosed in FIG. 1, may also include a series thermistor
112 in the inlet side of the line, a series thermistor unit 113 in
the outlet side of the system, an under temperature thermal switch
114 in the inlet side of the loop, as well as a thermometer 115, a
flow meter 116, and a pressure gauge 117 in the inlet side of the
loop. The outlet side of the loop may include a flow switch 118.
Individual thermometers 119 and 120 may be provided in the
individual outlets of the dummy loads prior to their
interconnection to the common outlet line, and individual
overtemperature switches 121 and 122 may also be provided in these
individual lines. If desired, a filter 123 may be removably coupled
to the primary loop by means of suitable valves.
The secondary loop of the arrangement of FIG. 3 is also essentially
the same as the secondary loop of FIG. 1, with the addition of
thermometers 130 and 131 in the two sides of the loop at the heat
exchanger 32, as well as pressure gauges 132 and 133 in each side
of the line at the input of the loop. A flow meter 134 may be
provided in the loop. In addition, a solenoid controlled valve 135,
controlled by a solenoid 136, may be provided for bypassing the
valves 46 and 47.
FIG. 4 illustrates a variation of a portion of the circuit of FIG.
1 which may be adaptable, for example, for use in the system of
FIG. 3. In this arrangement, the bridge circuit 60 is essentially
the same as that of FIG. 2, with the output of the bridge circuit
being connected to a watt meter indicator 140 for indicating the
power dissipation in the dummy loads. The output of the flow meter
116 of FIG. 3 is connected to a suitable converter 117 for
providing a suitable flow indication quantity to the watt meter
indicator, and a flow indicator 118 may be provided connected to
the converter 117 to provide visual indication of the flow. The
thermistors 112 and 113 are also connected to the watt meter
indicator to provide the necessary indication therein. In the
arrangement of FIG. 4, the relay control circuit, which controls
the application of power to the leads 74 and 75 from the source
lead 73, is comprised of a conventional optical meter relay control
circuit 119.
FIG. 5 illustrates an auxiliary circuit which may be employed in
combination with the system of FIG. 3. In this arrangement, the
flow switch 118 of FIG. 3 is connected to operate a relay 140, the
undertemperature switch 112 is connected to operate a relay 141,
the over-temperature switches 121 and 122 are serially connected to
operate a relay 142, and a pump control switch 143 (not shown in
FIG. 3) is connected to operate a relay 144. An additional relay
145 is provided having contacts for applying power to the pump 36.
In the arrangement of FIG. 5, the relay 144 is a delay relay, and
the switch 143 is connected to apply power to the pump relay 145 by
way of the normally closed contacts of the relay 144. In view of
the delay in this relay, the power will be applied to the pump in
this manner until the flow switch 118 operates to energize the
relay 140, whereupon the pump relay 145 will remain energized by
way of normally open contacts 150 of the relay 140. The pump 36
will thereby remain energized as long as the flow switch 118 in the
primary loop is closed, and failure of the flow or this switch will
effect the removal of power from the pump 36. Normally closed
contacts 151 of relay 140 also energizes a "standby" lamp 152. When
the flow of liquid in the primary loop is maintained, and the relay
140 thereby energized, an "operate" lamp 153 is energized by way of
the contacts 151 and normally closed contacts of the relay 141.
Over temperature of the liquid is indicated by a "temperature"
light 154, which is energized by way of normally closed contacts of
the relay 141, and normally open contacts of the relay 142. The
relay 142 is also provided with contacts 155 which are connected to
apply power to the solenoid 136 in the event of over temperature
indicated by the over-temperature switches 121 and 122, and as
illustrated in FIG. 3, this results in the rapid opening of the
solenoid valve 135 to bypass the valves 46 and 47, and thereby to
permit the maximum flow of liquid in the secondary loop 31.
In order to deenergize a transmitter in the event of excessive
temperature of the coolant, an interlock circuit for the
transmitter may be provided extending from interlock terminals 160
through normally open contacts of relays 140 and 142, normally
closed contacts of relay 141, and a manual switch 161.
While the invention has been disclosed with reference to particular
embodiments, it will be apparent that many modifications and
variations may be made therein without departing from the
invention, it is therefore intended in the following claims to
cover all such variations and modifications as fall within the true
spirit and scope of the invention.
* * * * *