Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1987-09-29
1989-12-19
Paschall, M. H.
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219497, 219499, 219505, 219210, 323366, H05B 102
Patent
active
048884715
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to devices for heating and thermal regulation of any body but more particularly of enclosures containing devices having operating characteristics which are very sensitive to temperature variations such as piezoelectric crystal oscillators.
2. Description of the Prior Art
A device for thermal regulation of an enclosure has already been disclosed in European patent No. 4,233 granted to the present Applicant. This device comprises a circuit for measuring the temperature of the enclosure and a circuit for heating said enclosure. The measuring circuit consists of a resistor bridge, one arm of which is provided with at least one heat-sensitive element, as well as an amplifier for delivering at its output a control signal which is representative of the difference between the measured temperature of the enclosure and a reference temperature, the absolute value of said control signal being adjusted by means of a negative feedback loop. The heating circuit is supplied from a voltage source and regulated by the temperature-measuring circuit. Said heating circuit is usually constituted by at least one voltage-stabilizing semiconductor circuit, a heating current being passed through said circuit and adjustable by means of a control transistor which is subjected to said control signal. In certain instances, the heating circuit can be constituted solely by the control transistor. In these two instances, the negative feedback loop of the output amplifier of the temperature-measuring circuit is taken directly from the output of said amplifier. The result thereby achieved is that the gain of the thermal regulation device must be adjusted for each product by reason of the dispersion of characteristics of the control transistor which is subjected to the control signal delivered by the output amplifier. A non-linear heating current which is a function of the control voltage is also observed.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a remedy for the deficiencies observed in the regulating device considered in the foregoing.
The invention is accordingly directed to an improvement in the device for thermal regulation of an enclosure as described in European patent No. 4,233, which consists in connecting the negative feedback loop of the output amplifier of the temperature-measuring circuit between the emitter resistor of the control transistor and the input of said amplifier.
By means of this arrangement, the voltage at the terminals of the emitter resistor is proportional to the signal applied to the noninverting input of the output amplifier of the temperature-measuring circuit.
In this case, the regulating system is no longer dependent on the electrical parameters of the control transistor and the current gain is related solely to the values of the emitter resistor, of the negative feedback resistor and of the measuring bridge resistors. This results in good reproducibility of the system.
The circuit assembly in accordance with the present invention can be employed in the thermal regulation device described in European patent No. 4,233. However, this assembly can also be employed in thermal regulation devices providing proportional-plus-integral-plus-derivative control action as described in French patent application No. 82.19584 filed in the name of the present Applicant. In the case of these regulating devices, when the feedback loop of the output amplifier consists of a resistor, it is necessary to compensate for the voltage drop at the terminals of this resistor. To this end, the inverting input of the amplifier is connected through a resistor to the output of the stabilized-voltage generator. However, in order to prevent saturation of the integral-action operational amplifier when the thermostat is regulating, it is necessary to adjust the value of the resistor provided on the inverting input of the output amplifier and the stabilized-voltage generator as a function of the reference temperature.
In acc
REFERENCES:
patent: 3942075 (1976-03-01), Maran et al.
patent: 4216371 (1980-08-01), Marotel
patent: 4236064 (1980-11-01), Aiba
patent: 4362924 (1982-12-01), Story et al.
patent: 4404462 (1983-09-01), Murray
patent: 4567353 (1986-01-01), Aiba
patent: 4629852 (1986-12-01), Andre
Compagnie d'Electronique et de Piezo-Electricite C.E.P.E.
Paschall M. H.
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