The disclosed apparatus includes a heat meter and a flow meter.
The heat meter includes means for delivering trains of pulses to
a heat register, the pulses per train being proportional to the
temperature difference between fluid inlet and outlet passages of
heat exchange means, and the recurrence rate of the pulse trains
being determined by a flow sensor. A visual indicator of the pulse
trains facilitates zero-difference adjustment of the temperature
sensors when they are both at the same temperature. Compensation
for variations in the specific heat of the fluid and temperature-related
inaccuracy of the flow sensor is effected by non-linear frequency
adjustment of an oscillator that generates the pulses. In a flow
meter (omitting the temperature-difference circuit) compensation
for temperature-related inaccuracy of flow-sensors is effected correspondingly.
What is claimed is:
1. Heat metering apparatus for a system having a heat exchanger,
an inlet passage, an outlet passage and means for moving fluid through
said inlet passage, said heat exchanger and said outlet passage
serially, said heat metering apparatus including a flow sensor at
one of said passages operative to produce a series of pulses in
response to fluid flow, a pair of temperature sensors located at
said inlet and outlet passages, respectively, temperature difference
means for taking the difference between the outputs of said temperature
sensors, an oscillator, a heat meter, product-taking means responsive
to both said flow sensor and said temperature difference taking
means for enabling the oscillator to supply trains of pulses to
the heat meter at intervals determined by said flow sensor for durations
determined by said temperature difference taking means, and monitoring
means including an indicator responsive to output pulses from said
product-taking means for indicating whether the temperature sensors
are virtually alike when both are subjected to the same temperature
and for monitoring the flow rate.
2. Apparatus as in claim 1 wherein said indicator is a light source.
3. Apparatus as in claim 1 wherein said monitoring means includes
a pulse-extender for causing a brief pulse from said product-taking
means to cause a prolonged interval of operation of said indicator.
4. Apparatus as in claim 3 wherein said indicator is a light-emitting
5. Apparatus as in claim 1 wherein said product-taking means includes
a ramp generator triggered by said flow sensor and gating means
responsive to said ramp-generator and said temperature-difference
taking means arranged to transmit oscillator pulse trains whose
lengths are proportional to the output of the temperature difference
taking means whereby, as the output of the temperature difference
taking means approaches zero, the number of pulses in each pulse
train approaches zero during their adjustment when the temperature
sensors are at the same temperature.
6. Apparatus as in claim 5 including a rectangular-wave generator
in the output of the flow sensor arranged during one level of its
output to drive and hold the ramp generator at its ramp-starting
phase and simultaneously to block oscillator pulses, said rectangular
wave generator being arranged during the other level of its output
to initiate the ramp generation and to enable oscillator-pulse output.
The present invention relates to apparatus for metering the heat
supplied to or delivered from heat-exchange means between inlet
and outlet passages, and to flow-metering apparatus.
In one aspect, the present invention is an improvement on my U.S.
Pat. No. 4224825 issued Sept. 30 1980 which relates to heat meters.
That patent discloses inlet and outlet temperature sensors and means
for taking the difference between those temperatures, a flow sensor
that emits electrical pulses corresponding to fluid-induced operation
of a rotor, a ramp generator that is triggered by flow-sensor pulses,
a high-frequency oscillator, a register, and temperature-difference-controlled
gating means that determines the number of oscillator pulses that
are entered into the register. To the extent applicable, and in
the interest of brevity, the disclosure in that patent is incorporated
herein by reference.
As disclosed in detail in that patent, the temperature sensors
are matched, and they are in respective circuits such that the output
of each sensor varies linearly with (in proportion to) temperature
and varies in the same magnitude over the operative temperature
range. An object of the present invention resides in providing an
indicator to evidence match of the outputs of the inlet and outlet
temperature sensors when they are at the same temperature, thereby
facilitating adjustment. A related object of the invention resides
in providing a single indicator for checking both the operation
of the flow sensor and matching adjustment of the temperature sensors.
Using such an indicator, one of the temperature sensors can be adjusted,
as necessary, to equal the output of the other at a given temperature.
This adjustment can be checked both at the factory and at the point
of use from time to time.
In making the adjustment, the two temperature sensors are exposed
to the same temperature. When the sensors are adjusted to produce
next-to-zero net output, only one or two high-frequency oscillator
pulses are emitted during each triggered ramp. An indicator is provided,
ideally a light source, at the point in the apparatus where the
succession of pulse trains enters the circuit of the heat meter
or register. This indicator is "on" at intervals when
there is a temperature difference and when the fluid is flowing.
When the inlet and outlet temperature sensors are at the same temperature,
one of the temperature sensors is adjusted so that output of a temperature-difference
means accurately equals zero as evidenced by extinction of indicator
The same indicator is also useful in checking the operation of
the flow meter since the frequency of indicator operation, especially
light bursts, represents the rate of operation of the flow-meter's
Accuracy of the temperature-sensor adjustment is dependent on the
sensitivity of the indicator. For enhanced sensitivity, the oscillator
in the apparatus is operated at a high frequency (much higher than
needed for registering heat units in the heat-unit counter that
displays heat units) and the indicator is connected at or near the
highest-frequency point in the circuit of the divider-and-counter
circuit. Adjusting a temperature sensor to extinction of a high-frequency
pulse gives more precise results than the same adjustment at low
With spaced-apart short-duration pulses to the indicator, each
pulse or brief pulse train may not keep the light source or other
indicator "on" long enough to be noted. Observation of
the "on" condition can better be assured by switching
the indicator "on" for a substantially longer time interval
than the duration of a high-frequency pulse, as by triggering "on"
a monostable indicator-actuating device. Here that purpose is realized
effectively by incorporating a pulse extender.
In my patent, a ramp signal is used in taking the product of the
inlet-outlet temperature difference and the number of pulses from
the flow meter. There the start of the ramp coincides with the discharge
of a capacitor in the ramp generator. An object of the present invention
resides in improving the accuracy of such apparatus, which is here
accomplished by discharging the capacitor in a preparatory operation,
followed by separately initiating the ramp. In this way there is
no need to speculate on the theoretical accuracy of full discharge
of the ramp-generating capacitor and the truly concurrent start
of the ramp. This change is implemented in part by blocking the
oscillator signal until the ramp is initiated.
In my patent mentioned above, it was noted that, while the register's
reading of delivered (or extracted) heat depends mainly on the product
of the temperature difference and the number of pulses from the
flow sensor, the operation is also affected by the non-linearly
varying specific heat of the fluid and by the temperature-dependent
variations in the rate of operation of the flow sensor. A form of
compensating means for the latter factors was provided in my patent.
Another object of the present invention resides in providing novel
and improved means for introducing compensation into the heat-metering
circuit for temperature-dependent variations in the operation of
the flow sensor and for variations in the specific heat of the fluid,
especially water. Noting that there are two factors in the product-taking
operation of the heat meter--temperature difference and flow rate--it
may be said that the compensation corrects for variations in the
flow sensor's response to the temperature-dependent variations in
the mass-flow rate of the fluid.
In the novel heat meter, the oscillator which produces high-frequency
pulses operates at a frequency that varies in dependence on one
of the temperature sensors, particularly the temperature sensor
at the flow sensor. The relationship between the signal derived
from the temperature sensor and the frequency of the oscillator
can be made to be a non-linear function that matches quite accurately
the temperature-dependent variations of the flow sensor in sensing
the mass rate of flow of the water or other fluid.
In one aspect of the present invention, improved accuracy of the
heat meter is provided by introducing compensation for temperature-dependent
inaccuracies of the flow meter. A further object of the present
invention resides in providing flow meters with the same kind of
compensation for temperature-dependent variations in volume-flow
The accompanying drawing shows a presently preferred yet illustrative
embodiment of the present invention in its various aspects. Those
components in the drawing that are not specifically mentioned below
are to be regarded as incorporated in the description in accordance
with their conventional symbols.
In the drawing, high-temperature sensor 10 and low-temperature
sensor 12 are installed in intimate temperature-transfer relation
to inlet and outlet fluid passages, especially in a circulating
water system supplied by a furnace (for example) to heat-exchange
means such as radiators, or a hot-water supply system including
a heater such as a solar heater. The high and low temperature sensors
are connected to the (+) and (-) input terminals, respectively,
of differential amplifier 14 here an operational amplifier. Temperature
sensing elements 10a and 12a in temperature sensors 10 and 11 are,
for example, integrated circuit elements LM 135. The temperature
sensors are adapted to produce an output voltage that varies linearly
with temperature, e.g. varying from about 2.73 volts to 3.73 volts
in proportion to a temperature range of 0.degree. C. to 100.degree.
C. The output of amplifier 14 may vary, with this 0 to 1-volt input
differential, over a range of 0 volts to 10 volts.
A ramp signal generator is periodically triggered by a pulse from
flow-detector 18 preferably via frequency divider 20. Flow detector
18 includes a flow-activated rotor. It may assume many forms, designed
to produce output pulses in proportion to the volume of fluid flow.
The ramp generator 16 here includes a junction field-effect transistor
16a, a capacitor 16b and a constant-current generator 16c, all as
described in my patent mentioned above. While transistor 16a has
"high" input, it discharges capacitor 16b and maintains
the capacitor discharged. This results from "high" intervals
in the rectangular wave of the divider. With "low" divider
output, transistor 16a is rendered non-conducting. The ramp signal
is promptly started as capacitor 16b starts to charge through its
constant-current source 16c. While divider 20 maintains transistor
16a conducting, the divider also acts via blocking diode 25 and
connection 27 to maintain capacitor 24d of oscillator 24 charged,
blocking the oscillator.
Signals A from ramp generator 16 and the output of differential
amplifier 14 are supplied to the (-) and (+) inputs, respectively,
of comparator 22 whose output shifts between "high" and
"ground". For zero temperature difference, the voltage
at the (+) input of comparator 22 matches the discharge voltage
of capacitor 16b, this being the downward peak of the truncated
saw-tooth wave A. When the output of divider 20 shifts "high",
connection 27 through blocking diode 25 blocks oscillator 24.
When the output of divider 20 goes "low", oscillator-blocking
connection 27 has no further effect. If the temperature difference
between the inlet and outlet passages is small, then comparator
22 yields an enabling or gating bias for signals of oscillator 24
at terminal 26 during only a short time interval. The "on"
time interval of the gate and the length of oscillator pulse trains
increase linearly with the temperature difference. Oscillator pulses
are provided by inverting Schmitt trigger 28 at output terminal
Thus far, it is apparent that the output of oscillator 24 is enabled
or gated "on" during each truncated saw-tooth wave for
a time interval that is proportional to the inlet-outlet temperature
difference, and the number of truncated saw-tooth pulses is primarily
proportional to the fluid flow. Consequently the total number of
oscillator pulses at terminal 29 is proportional to the product
of the flow rate, and the temperature difference. Where the specific
heat is taken into account, this pulse-train total also represents
the heat units extracted from the fluid between the inlet and the
outlet in case of a heating system, as well as the heat units added
to the fluid in case of a solar hot-water heating system or a room-
or apartment cooling system. This output is delivered to a BTU register
31 comprising successive frequency dividers 30 and 32 and BTU counter
34. The dividers are chosen to make counter 34 read directly in
One of the temperature sensing elements 10a or 10b is installed
at the flow sensor, which is advantageously located in the return
line in the case of a circulating hot-water heating system.
The actual numbers of BTU's that are registered by the system thus
far described depends importantly on the specific heat of the water
whose volume is measured by operation of flow sensor 18. The specific
heat of water varies non-linearly with the water temperature. The
disclosed apparatus provides a means for compensating for this non-linearity
and for other temperature-related factors that cause the flow sensor's
signals to deviate from actual volume-flow or mass-flow of the water
or other fluid.
A signal from the flow sensor's temperature sensor provides input
bias to operational amplifier 36. The selection option is diagrammatically
illustrated by selection means 38 having dotted-line connections
to the two temperature sensors. For example, the input to amplifier
36 is taken from the low-temperature sensor whose sensing element
12a is installed at the fluid-flow sensor. The output of amplifier
36 is a proportionally amplified representation of the temperature
sensor's output, thus proportional to temperature change. Where
this linear voltage is impressed on oscillator 24 the variation
of oscillator frequency can be made non-linear in virtually the
exact manner that specific gravity is a non-linear function of temperature.
The same compensation can take into account additional temperature-induced
deviations of the flow sensor for proportional response to flow
at different temperatures. The manner of non-linear (non-proportional)
variation of oscillator frequency with changing output of amplifier
36 is discussed below.
Temperature sensors 10 and 12 are chosen to have near-identical
output variations, proportional to temperature. There should be
zero output from comparator 14 and there should be no oscillator
pulses at point 26 in the circuit when the two sensors are at the
same temperature. The present apparatus includes built-in means
for determining that this is true, useful both at the factory for
calibration and at the point of use for verification and for corrective
adjustment. In making a test, both temperature sensing elements
may be immersed in the same volume of water to be at the same temperature,
and a flow-simulating signal is supplied to ramp generator 16. An
adjustable resistor 10b in temperature sensor 10 is then adjusted
from a no-output condition at terminal 26 until output pulses just
start to appear or the resistor may be adjusted until the output
pulses just disappear. This is evidenced by an LED indicator 40
that provides light flashes in response to input voltage pulses
or pulse trains, acting through pulse extender 41.
For maximum sensitivity and precision, the temperature-sensor adjustment
is made by monitoring the signals at the highest-frequency part
of the system, i.e. at terminal 29 where trains of pulses of oscillator
frequency appear when there is an inlet-output temperature-difference
signal and when fluid flows. While the signals appearing at points
along the frequency-divider channel 30 32 are longer in duration
than the pulses at terminal 26 or 29 many oscillator pulses may
be required to produce each frequency-divided signal. Thus, monitoring
the signals developed along the divider channel would represent
a loss of sensitivity when zero temperature-difference output is
approached in making a zero adjustment.
When resistor 10b of temperature sensor 10 is in next-to-perfect
adjustment, the output pulses (e.g. 60 to 70 kHz) reaching terminal
29 are--or should be--extremely brief, and therefore they would
not activate LED indicator 40 noticeably. To attain maximum sensitivity
of the indicator while assuring visible light output during zero
adjustment, a pulse extender 41 is included between the gated oscillator-output
terminal 29 and the indicator. A fixed or variable pulse-extender
may be used to provide prominent response under the marginal condition
of zero adjustment when only a few oscillator pulses comprise each
A variable pulse extender is provided in the apparatus represented
in the drawing. The pulse extender is effective to turn "on"
the LED 40 for a minimum time interval that is long enough to assure
visibility in response to only single pulses of oscillator frequency
recurring at the rate of the (divided) flow-sensor signal. When
a pulse train is generated at each flow-sensor signal, the "on"
time of the LED is equal to the minimum extended time interval plus
the duration of the pulse train. Schmitt trigger 28 delivers a pulse
via blocking diode 42 to discharge capacitor 44 almost instantly,
after which the capacitor charges gradually through resistor 46.
(When there is a succession of oscillator pulses in each pulse train,
charging of capacitor 44 is delayed until the last pulse of the
train has passed.) Capacitor 46 is quite small, for assurance that
it has been virtually discharged by Schmitt trigger 28 in response
to even a single oscillator pulse from comparator 22 for example
12 .mu.Sec. Capacitor 44 is therefore very small, e.g. 220 pf. Even
with a resistor 46 of 10 megohms, the time constant tends to be
too short to maintain a visible output from indicator 40. Inverting
Schmitt trigger 48 and blocking diode 50 operate to charge capacitor
52 while capacitor 44 remains nearly discharged. The charge on capacitor
52 drains slowly through parallel resistor 54 a time period much
longer (e.g. 20 milliseconds) than the short output pulses of comparator
22. Another inverting Schmitt trigger 56 energizes LED indicator
40 so long as capacitor 52 remains sufficiently charged. It follows
that the LED indicator will be "on" in response to only
a single pulse of oscillator 24 and in response to a pulse train.
Only one or two pulses per ramp signal will reach terminal 26 when
temperature sensors 10 and 12 produce nearly identical output. The
LED indicator will flash in response to each ramp signal for the
duration of the minimum time interval of the extended pulse. That
interval is increased for a further period when there is a significant
temperature difference between the two sensors 10 and 12 giving
an impression of greater brightness. Moreover, in normal operation
of the heat meter, the frequency of light flashes of the LED will
correspond to the rate-of-flow of the water or other fluid. The
indicator flashes are thus useful as a check on the fluid flow and
on the temperature-sensor adjustment.
Flow detectors are often of the type that produce a pulse in response
to each blade of a fluid-activated turbine rotor passing a detector.
That would be of such high frequency that the LED would seem to
be "on" continuously. Among its other purposes, frequency
divider 20 limits the frequency of pulses reaching the LED indicator
so that it emits separated flashes even when there is a high flow
It was noted above that oscillator 24 can be made to operate at
a frequency that is variable as a function of the temperature at
the flow-sensor location, and that amplifier 36 provides a voltage
to oscillator 24 that varies in proportion to the temperature changes.
For example, the voltage input to amplifier 36 may vary over a range
of 1.0 volt for a temperature-difference variation of 0.degree.
C. to 100.degree. C. Amplifier 36 may correspondingly have an output
that changes from 5 to 10 volts, a 5-volt range for a temperature
change of 0.degree. C. to 100.degree. C. The (+) input of comparator
24a in the oscillator has a bias established by a bias resistor
network including voltage divider 24f, 24g, modified by the output
of amplifier 36 via resistor 24h. Comparator 24 has a feedback loop
to its (+) input via resistor 24a. Comparator 24 also has a feedback
loop to its (-) input including fixed and adjustable resistors 24b
and 24 c in series, connected in series wih capacitor 24d to ground
(d-c negative). A resistor 24e connects the resistor-capacitor circuit
24b-c-d to the (+) d-c supply terminal.
Oscillator 24 produces rectangular waves as the (-) input of comparator
24a rises above and falls below the bias at the (+) terminal. When
the output of comparator 24a is low, due to the (-) terminal having
risen above the bias potential at the (+) terminal, the output point
of comparator 24a is virtually at ground potential and the capacitor
starts to discharge. After this discharge has carried the (-) terminal
below the potential at the (+) terminal by a discrete differential,
the output of the comparator goes high. Its output terminal is biased
positively via resistor 24e. Consequently, capacitor 24d develops
a progressively increasing charge voltage, terminating when, once
again, the potential at the (-) terminal exceeds the bias at the
The operation of the oscillator at various output voltages of amplifier
36 may be considered. For discussion let it be assumed that the
(+) terminal of the comparator is biased near the (+) terminal voltage
of the d-c supply. When comparator 24a drives its output to ground,
that output drops from near d-c positive potential. The capacitor
was charged to a relatively high voltage, so the capacitor tends
to discharge rapidly. After a discrete drop in the capacitor voltage,
the comparator turns "on". Due to rapid discharge, the
"off" time is short. The capacitor voltage then rises,
but because its voltage remained relatively high, it charges slowly,
If it now considered that the (+) terminal of comparator 24a is
biased by amplifier 36 via resistor 24h well below the (+) terminal
of the d-c supply, a different operating condition develops. With
the comparator switched "high", capacitor 24d charges
to a close approximation of the bias at the (+) input of the comparator.
Upon switching of the output of of comparator 24a to ground potential,
capacitor 24d discharges somewhat slower than in the first example,
its charge at switchover being at a lower voltage than before. After
a somewhat longer discharging time interval than before, the (-)
input of the comparator drops by a discrete value below the potential
at the (+) input terminal, the output point of the comparator switches
"high", and charging of capacitor 24d is resumed. However,
the output point of the comparator is at a much higher potential
at this time than the capacitor potential, so that recharging tends
to be more rapid than in the first condition.
In practice, the following frequency variation of the oscillator
occurs as a function of the water temperature of the flow sensor
in a practical example:
______________________________________ % 0 -0.5 -1.0 -1.5 -2.0
-2.5 -3.0 -3.5 Freq. .degree. C. 0 39.3 53.6 67.9 75.0 83.9 91.1
From this data, the non-linearity of the frequency change in response
to various temperatures is striking. The temperature rises as much
as 39.3.degree. C. in causing the first 0.5% frequency change. The
temperature rises only 8.9.degree. C. in causing the last 0.5% frequency
change. (All percentages are based on the frequency at 0.degree.
The foregoing data was obtained by setting the bias of the (+)
input of comparator 24 at 4.4 volts at 0.degree. C. The curvature
of the temperature-frequency characteristic can be varied by adjusting
the (+) input to other bias voltages at 0.degree. C., to compensate
for the resultant effects over a range of temperatures of the change-of-specific-gravity,
the change of apparent viscosity of the fluid as it affects the
flow sensor, and other temperature-dependent factors.
Truncated Saw-tooth Generator
It was indicated above that frequency divider 20 goes "high"
and "low" for alternating intervals. The change from low
to high turns on transistor 16a, causes discharge of capacitor 16b
and maintains the discharge for a stabilizing time period. During
that time interval, the (-) input of comparator 22 allows the comparator
output to go high so that the output of oscillator 24 is high. The
oscillator would thus operate well in advance of the ramp portion
of curve A. However, the "low" output of frequency divider
20 at this time also acts via blocking diode 25 and connection 27
to prevent charging of capacitor 24d, thus blocking the oscillator.
Instantly when the output of frequency divider goes "low"
and turns-off transistor 16a, thus allowing recharging of capacitor
16b and starting the ramp in curve A, blocking diode 25 frees oscillator
22 to oscillate. The truncated saw-tooth characteristic A avoids
inaccuracy that may arise with a saw-tooth wave, where discharge
of the ramp-generating capacitor and the start of the recharging
phase occur simultaneously.
The frequency divider 20 serves as a generator of rectangular-waves
B, in which the "low" and "high" output phases
can have various durations, as desired. The "low" time
interval should be made long enough in relation to the ramp of curve
A so that the output of the divider does not go "high"
before the ramp voltage rises above the temperature-difference voltage
at the inputs to comparator 22 at the maximum flow rate and temperature-difference
of the apparatus.
The temperature-dependent factors underlying varied flow-meter
response to a given volume of fluid flow can be compensated by means
of virtually the same circuit as in the heat meter described above.
Additionally, if the flow-meter is to indicate mass-rate-of-flow,
the compensation can additionally take into account the variations
of specific heat of the fluid, e.g. water, at different temperatures.
For this purpose, the two-position three-pole switch 60a, 60b and
60c can be shifted from the position shown, in which the apparatus
operates as a heat meter, into the other position in which the apparatus
serves as a flow-meter. In the changed switch position, the output
of frequency divider 20 activates timer 62 for a precise time interval
to apply a potential to the (-) input of comparator 22 below that
provided at the (+) input by voltage divider 64. During the same
interval, connection 27 frees the oscillator to oscillate. The oscillator
output reaches frequency divider 66 via switch section 60c to operate
flow-rate meter 68 and flow volume indicator 70. The latter may
be calibrated as a mass-flow indicator.
As in the heat meter, the temperature sensor at the flow-meter
is connected to amplifier 36 so as to adjust the oscillator frequency
in accordance with fluid temperature. The oscillator frequency at
different temperatures can be modified empirically to compensate
for temperature-dependent factors affecting the operation of the
The drawing combines a flow-meter with a heat meter, primarily
to emphasize parallels that should be recognized between compenstion
in the two instruments. The two instruments combined as shown could
be used together where required.
The foregoing embodiments of the various features of the invention
will be found useful in various modified forms and certain of them
may be used without the others, so that the invention should be
construed broadly in accordance with its full spirit and scope.