Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-02-25
2001-05-22
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S587000, C340S588000, C340S589000, C374S173000, C374S178000, C374S183000, C374S185000
Reexamination Certificate
active
06236320
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for determining whether an ambient temperature is higher or lower than a predetermined threshold temperature.
2. Description of the Related Art
Electrical equipment has a defined temperature range in which normal operation is allowed. Thus, some electrical equipment contains a temperature determining apparatus which determines whether an ambient temperature is higher or lower than a predetermined threshold temperature.
In such electrical equipment, when the temperature determining apparatus determines that an ambient temperature exceeds a range in which its operation is ensured, forced termination of operation is performed for preventing a malfunction, or recording of histories is performed for checking user environments, for example. While the aforementioned temperature determining apparatuses include products which operate mechanically, the temperature determining apparatuses which operate electrically are generally utilized.
A prior art example of such an electrical temperature determining apparatus will be hereinafter described with reference to
FIGS. 1 and 2
. As shown in
FIG. 1
, a prior art temperature determining apparatus
100
comprises a resistance element
102
, a diode
103
, a reference voltage generating circuit
104
, and a comparator circuit circuit
105
.
Resistance element
102
and diode
103
are connected in series between an operating voltage Vdd for an electrical equipment and the ground. Reference voltage generating circuit
104
generates a reference voltage Vref from the operating voltage Vdd which is lower than the latter. One input terminal of comparator circuit
105
is connected with the junction between resistance element
102
and diode
103
, and the other input terminal of comparator circuit
105
is connected with the output of reference voltage generating circuit
104
.
Resistance element
102
has a predetermined temperature-resistance characteristic in which a resistance value varies with a change in an ambient temperature. Thus, a change in the ambient temperature causes a change in a divided voltage VD generated by resistance element
102
and diode
103
from the operating voltage Vdd. The values of Vdd and Vref are set and the temperature-resistance characteristic of resistance element
102
is selected such that the divided voltage VD is equal to the reference voltage Vref at a predetermined threshold temperature.
Comparator circuit
105
compares the divided voltage VD with the reference voltage Vref and outputs a signal indicative of whether the ambient temperature is higher or lower than the threshold temperature.
As shown in
FIG. 2
, the reference voltage Vref is constant in a range “a” in which the operating voltage Vdd exceeds Vdd
0
. Furthermore, when the operating voltage Vdd is changed depending on the specification of the electrical equipment or the like, the reference voltage Vref is also changed in accordance with the operating voltage Vdd even if the ambient temperature is constant. As a result, the range of the operating voltage Vdd in which a temperature can be determined, is limited to, for example a range “b” in FIG.
2
.
Additionally, since the reference voltage Vref generated by reference voltage generating circuit
104
is temperature-dependent, the reference voltage Vref varies with a change in the ambient temperature, independently of the divided voltage V
0
. As a result, it is difficult for the temperature determining apparatus
100
to accurately determine whether an ambient temperature is higher or lower than the threshold temperature.
It is obvious that the aforementioned problems similarly occur in the temperature determining apparatus with a second resistance element in place of diode
103
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a temperature determining method and apparatus capable of accurately determining whether an ambient temperature is higher or lower than a threshold temperature.
The temperature determining apparatus according to the present invention comprises a first resistance-series circuit including a first and second resistance elements connected in series to each other, a second resistance-series circuit including a third and fourth resistance elements connected in series to each other, a voltage generating circuit, and a comparator.
The first and second resistance elements connected in series to each other in the first resistance-series circuit have different temperature-resistance characteristics. Thus, a change in an ambient temperature causes a change in the ratio of resistance values of the first and second resistance elements. On the other hand, the third and fourth resistance elements connected in series to each other in the second resistance-series circuit have the same temperature-resistance characteristic. Thus, the ratio of resistance values of the third and fourth resistance elements is not changed even when an ambient temperature is changed.
The voltage generating circuit applies the same reference voltage to the both ends of the first and second resistance-series circuits. The comparator circuit compares a first divided voltage generated at a junction between the first and second resistance elements with a second divided voltage generated at a junction between the third and fourth resistance elements to determine whether the ambient temperature is higher or lower than a predetermined temperature.
If the ambient temperature is not changed, a voltage output from the voltage generating circuit is constant even when an operating voltage is changed, and hence the first and second divided voltages are not changed. For this reason, it is possible to accurately determine whether the ambient temperature is higher or lower than the threshold temperature over a wide range of the operating voltage.
Additionally, even when a voltage output from the voltage generating circuit is changed due to the ambient temperature, the first and second divided voltages are not individually changed but interactively changed, so that a relative change in the divided voltage is small, thereby making it possible to accurately determine whether the ambient temperature is higher or lower than the threshold temperature.
According to an embodiment of the present invention, the temperature-resistance characteristics of the second resistance element is identical to those of the third and fourth resistance elements. Therefore, as the ambient temperature varies, the first divided voltage is obviously changed, while the second divided voltage remains constant. Accordingly, it is possible to accurately determine whether the ambient temperature is higher or lower than the threshold temperature.
According to a yet another embodiment of the present invention, the temperature-resistance characteristics of the second to fourth resistance elements are lower than that of the first resistance element. Therefore, when the ambient temperature varies, the resistance value of the first resistance element is changed lower than the resistance values of the second to fourth resistance elements. Thus, it is possible to reliably determine whether the ambient temperature is higher or lower than the threshold temperature with a simple configuration.
According to a still yet another embodiment of the present invention, the voltage generating circuit includes a power supply circuit for generating a predetermined power supply voltage, and an amplifier circuit for amplifying the power to said voltage. Therefore, it is possible to generate the voltage appropriate for the determination of a temperature.
In a yet further embodiment of the present invention, the power supply circuit includes a means for producing the constant power supply voltage if the operating voltage supplied from the outside is equal to or higher than the predetermined voltage. Therefore, it is possible to accurately determine the ambient temperature.
The above and other objects, features and advantages of the present invention will
Hayes Soloway Hennessey Grossman & Hage PC
Hofsass Jeffery
NEC Corporation
Nguyen Hung
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