GB1562582A

GB1562582A - Circuits responsive to temperature difference

Info

Publication number: GB1562582A
Application number: GB16201/78A
Authority: GB
Original assignee: Heimann GmbH
Current assignee: Heimann GmbH
Priority date: 1977-04-26
Filing date: 1978-04-25
Publication date: 1980-03-12
Also published as: SE7804739L; DE2718587A1; DK179578A; FR2389110A1

Description

(54) IMPROVEMENTS IN OR RELATING TO CIRCUITS RESPONSIVE TO TEMPERATURE DIFFERENCES (71) We, HEIMANN GMBH, a German Company of 6200 Wiesbaden, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to circuits responsive to temperature differences.

Measuring devices are required to calculate the heat consumption of central heating boilers in rented premises. Currently two systems are mainly in use.

In one system, a sensing element is used to determine the temperature difference AT between the outflowing water and the returning water of a central heating boiler.

In addition, a flowmeter measures the quantity of water M which has flowed through.

Multiplication of AT by M produces a quantity which represents the consumed quantity of heat.

In another system, the evaporation of a suitable liquid in the course of, for example, one heating period is measured. That is to say that the evaporated quantity of liquid serves as an analogue of the heat consumption. This liquid is contained in a tube which stands in good heat contact with the boiler.

Both systems have disadvantages.

Although the first system operates physically satisfactorily and extremely accurately, it is expensive to install and for reasons of cost can be used only for large dwellings.

The consumed quantity of water M can be metered in a simple fashion. However, the formation of the product of M with the temperature difference AT must be continuously carried out over the entire measurement period, as the temperature difference normally changes with time. Integration cannot be carried out until following the evaluation of the variation of throughflow as a function of temperature difference.

The second system, on the other hand, is extremely cheap but physically inaccurate as the analogue value is a measure only of the product of the temperature of the heater and the time during which the heater allows the liquid to evaporate, and not of the quantity of heat emitted as a result of the temperature difference between the heater and surrounding air at greater or lesser degrees of coolness. Furthermore, this measurement is adulterated by the fact that when the surrounding air is greatly cooled the heater likewise cools. Consequently, the evaporation rate of the measuring liquid falls and simulates a low heat consumption. Similarly surrounding air which is already warm simulates heat output from the heater.

According to the invention, there is provided a circuit comprising two thermojunctions connected in series with a charge flow measuring device whereby the quantity of charge measured by the device is the time integral of current flowing as a result of temperature difference between said thermo-junctions.

Preferably, said thermo-junctions are formed by a first wire of a first metal and two further wires of a second metal joined to the first wire at respective spaced positions thereof.

Each thermo-junction may be formed by soldering or by welding.

Preferably, said device operates by deposition of metal from solution in response to current flow, the quantity of metal deposited being a measure of the quantity of charge which has flowed.

Expediently, a plurality of pairs of thermo-junctions are connected in series to form a thermocolumn.

Preferably, a rectifier element is connected in series with said device.

Preferably, each thermo-junction and/or charge measuring device and rectifier element is or are provided with an extruded electrically insulating casing.

Said casing may be of soft synthetic resin material.

For a better understanding of the invention and to show how the same may be carried into effect reference will now be made by way of example to the accompanying drawing in which: Figure 1 schematically illustrates a measuring device in accordance with the invention; Figure 2 illustrates schematically the application of the device of Figure 1 to a radiator; and Figure 3 illustrates schematically a further device in accordance with the invention.

In Figure 1, a thermoelement is formed by metallic wires 1, 2 and 3. Wires 1 and 3 are of the same material, for example iron, and wire 2 is for example, of constantan.

Wires 1 and 3 are soldered or welded each to a respective end of wire 2 at the positions 4 and 5 thus forming two thermo-junctions.

When positions 4 and 5 are at unequal temperatures, a thermo-electric voltage arises between them. Between the respective other ends of wires 1 and 3 is connected a series arrangement of a charge measuring tube 6 and a diode 7. Diode 7 ensures that a current flows only in one direction and thus prevents the charge measuring tube 6 from being affected by current which would otherwise flow in the event of an inverse temperature difference between the positions 4 and 5, for example when surrounding air is warmer than the radiator itself.

The charge measuring tube 6 contains a metal salt solution (such as for example copper sulphate solution), between two metal electrodes. Any current flowing through the tube 6 then causes the cathode to grow by deposition of copper. The amount of deposition then represents a gauge of the quantity of charge which has flowed. If furthermore, at least the anode consists of copper, the current flow cause copper from the anode to go into solution.

Because copper is thus constantly returned to the copper sulphate solution, deposition rate for a fixed current remains constant.

Figure 2 illustrates the installation of the measuring device in a heater 8. One thermo-junction 4 of the thermo-element stands in good heat contact with the heater 8, whereas the other junction 5, spaced from the heater 8 at a distance of, for example, 10 cm, is at the temperature of the surrounding air. The tube 6 is also arranged at the position of junction 4.

Figure 3 illustrates the arrangement of five thermo-junction pairs to form a thermo-column for increased sensitivity.

Similar pairs of wires 1 and 2 are connected in series, and the solder or welding positions lie alternately at 4 and 5. A charge flow measuring tube 6 with a diode 7 is again provided. In this arrangement, the individual thermo-electric voltages are additive.

This shortens the measuring time. The wires 1, 2 and 3, the measuring tube 6 and the diode 7 can advantageously be provided with an extruded covering for example of soft synthetic resin material.

A numerical example will further explain operation of the measuring circuit. It will be assumed that a mean temperature difference of 10 C exists between heater 8 and surrounding air beneath the heater 8. An individual thermo-element consisting of iron-constantan wire supplies a thermoelectric voltage of 0.5 mV, so that a thermo-column comprising 20 thermoelements supplies 10 mV. With an internal resistance of about 500Q for measuring tube 6, a current of 20,u A flows. Inside the measuring tube, this current forms a copper rod having a length of about 30 mm by deposition provided this temperature difference is maintained for about 2000 hours. As one measurement period has a duration of about 180 days, with a heating period of 10 hours each day, the measuring tube 6 would be 90% used after 1800 hours.The read-out accuracy is about 5%.

Thus suitably the measuring device is provided with at least one thermo-element, wherein two wires consisting of different metal are connected to one another for example by soldering at two points. One solder point is applied to a heater whereas the other is thermally connected to the heat receiver such as the surrounding air of the heater. In this manner a thermo-electric voltage produced in the thermo-element corresponds to the temperature difference between heat source and heat receiver. Thus a charge flow measuring device which carries out a time integrating function and in which deposition of a metal is effected by current flowing in response to the thermo-electric voltage, provides a measure of heat supplied by the heat source to the heat receiver.

The current produced by the thermoelectric voltage is proportional to the difference between the temperature of the heat source and that of the heat receiver, and consequently represents a physically correct gauge of the emitted quantity of heat. To ensure that only the heat flow out of the heater - to the environment is measured, a rectifier element may be connected into the circuit. Then the time integration of this current is an accurate gauge of the quantity of heat emitted from the heat source.

WHAT WE CLAIM IS: 1. A circuit comprising two thermojunctions connected in series with a charge flow measuring device whereby the quantity of charge measured by the device is the time integral of current flowing as a result of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. electrically insulating casing. Said casing may be of soft synthetic resin material. For a better understanding of the invention and to show how the same may be carried into effect reference will now be made by way of example to the accompanying drawing in which: Figure 1 schematically illustrates a measuring device in accordance with the invention; Figure 2 illustrates schematically the application of the device of Figure 1 to a radiator; and Figure 3 illustrates schematically a further device in accordance with the invention. In Figure 1, a thermoelement is formed by metallic wires 1, 2 and 3. Wires 1 and 3 are of the same material, for example iron, and wire 2 is for example, of constantan. Wires 1 and 3 are soldered or welded each to a respective end of wire 2 at the positions 4 and 5 thus forming two thermo-junctions. When positions 4 and 5 are at unequal temperatures, a thermo-electric voltage arises between them. Between the respective other ends of wires 1 and 3 is connected a series arrangement of a charge measuring tube 6 and a diode 7. Diode 7 ensures that a current flows only in one direction and thus prevents the charge measuring tube 6 from being affected by current which would otherwise flow in the event of an inverse temperature difference between the positions 4 and 5, for example when surrounding air is warmer than the radiator itself. The charge measuring tube 6 contains a metal salt solution (such as for example copper sulphate solution), between two metal electrodes. Any current flowing through the tube 6 then causes the cathode to grow by deposition of copper. The amount of deposition then represents a gauge of the quantity of charge which has flowed. If furthermore, at least the anode consists of copper, the current flow cause copper from the anode to go into solution. Because copper is thus constantly returned to the copper sulphate solution, deposition rate for a fixed current remains constant. Figure 2 illustrates the installation of the measuring device in a heater 8. One thermo-junction 4 of the thermo-element stands in good heat contact with the heater 8, whereas the other junction 5, spaced from the heater 8 at a distance of, for example, 10 cm, is at the temperature of the surrounding air. The tube 6 is also arranged at the position of junction 4. Figure 3 illustrates the arrangement of five thermo-junction pairs to form a thermo-column for increased sensitivity. Similar pairs of wires 1 and 2 are connected in series, and the solder or welding positions lie alternately at 4 and 5. A charge flow measuring tube 6 with a diode 7 is again provided. In this arrangement, the individual thermo-electric voltages are additive. This shortens the measuring time. The wires 1, 2 and 3, the measuring tube 6 and the diode 7 can advantageously be provided with an extruded covering for example of soft synthetic resin material. A numerical example will further explain operation of the measuring circuit. It will be assumed that a mean temperature difference of 10 C exists between heater 8 and surrounding air beneath the heater 8. An individual thermo-element consisting of iron-constantan wire supplies a thermoelectric voltage of 0.5 mV, so that a thermo-column comprising 20 thermoelements supplies 10 mV. With an internal resistance of about 500Q for measuring tube 6, a current of 20,u A flows. Inside the measuring tube, this current forms a copper rod having a length of about 30 mm by deposition provided this temperature difference is maintained for about 2000 hours. As one measurement period has a duration of about 180 days, with a heating period of 10 hours each day, the measuring tube 6 would be 90% used after 1800 hours.The read-out accuracy is about 5%. Thus suitably the measuring device is provided with at least one thermo-element, wherein two wires consisting of different metal are connected to one another for example by soldering at two points. One solder point is applied to a heater whereas the other is thermally connected to the heat receiver such as the surrounding air of the heater. In this manner a thermo-electric voltage produced in the thermo-element corresponds to the temperature difference between heat source and heat receiver. Thus a charge flow measuring device which carries out a time integrating function and in which deposition of a metal is effected by current flowing in response to the thermo-electric voltage, provides a measure of heat supplied by the heat source to the heat receiver. The current produced by the thermoelectric voltage is proportional to the difference between the temperature of the heat source and that of the heat receiver, and consequently represents a physically correct gauge of the emitted quantity of heat. To ensure that only the heat flow out of the heater - to the environment is measured, a rectifier element may be connected into the circuit. Then the time integration of this current is an accurate gauge of the quantity of heat emitted from the heat source. WHAT WE CLAIM IS:

1. A circuit comprising two thermojunctions connected in series with a charge flow measuring device whereby the quantity of charge measured by the device is the time integral of current flowing as a result of

temperature difference between said thermo-junctions.

2. A circuit according to Claim 1 wherein said thermo-junctions are formed by a first wire of a first metal and two further wires of a second metal joined to the first wire at respective spaced positions thereof.

3. A circuit according to Claim 2 wherein each thermo-junction is formed by soldering.

4. A circuit according to Claim 2 wherein each thermo-junction is formed by welding.

5. A circuit according to any one of Claims 1 to 4 wherein said device operates by deposition of metal from solution in response to current flow, the quantity of metal deposited being a measure of the quantity of charge which has flowed.

6. A circuit according to any one of Claims 1 to 5 wherein a plurality of pairs of thermo-junctions are connected in series to form a thermocolumn.

7. A circuit according to any one of the preceding Claims wherein a rectifier element is connected in series with said device.

8. A circuit according to any one of the preceding Claims wherein each thermojunction and/or charge measuring device and rectifier element is or are provided with an extruded electrically insulating casing.

9. A circuit according to Claim 8 wherein said casing is of soft synthetic resin material.

10. A circuit substantially as hereinbefore described with reference to the accompanying drawing.

11. The combination of a heating device and a circuit according to any one of the preceding claims, at least one thermojunction being in thermal contact with the heating device and at least one further thermejunction being in thermal contact with medium receiving heat from said heating device.

12. A combination according to Claim 11 wherein said heating device is a central heating boiler.