CA1165140A - Temperature sensing circuit - Google Patents
Temperature sensing circuitInfo
- Publication number
- CA1165140A CA1165140A CA000370243A CA370243A CA1165140A CA 1165140 A CA1165140 A CA 1165140A CA 000370243 A CA000370243 A CA 000370243A CA 370243 A CA370243 A CA 370243A CA 1165140 A CA1165140 A CA 1165140A
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- Prior art keywords
- resistor
- output terminal
- amplifying means
- input terminal
- input
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
TEMPERATURE SENSING CIRCUIT
ABSTRACT OF THE DISCLOSURE
An improved temperature sensing circuit is disclosed comprising a power supply which forward biases a diode sensing element to control the gain of an oparational amplifier. A temperature change causes the resistance of the diode to change, which changes its current flow. Since the anode of the diode is connected to the operational amplifier, the result is that the operational amplifier has a very linear output voltage proportional to temperature.
ABSTRACT OF THE DISCLOSURE
An improved temperature sensing circuit is disclosed comprising a power supply which forward biases a diode sensing element to control the gain of an oparational amplifier. A temperature change causes the resistance of the diode to change, which changes its current flow. Since the anode of the diode is connected to the operational amplifier, the result is that the operational amplifier has a very linear output voltage proportional to temperature.
Description
1 ~ ~5 1~ 0 TEMPERATURE SENSING CIRCUIT
Field Of The Invention .
Thls invention relates to temperature sensing circuits, and particularly to such temperature sensing circuits, utilizing a diode sensor.
Description Of The Prior Art Conventional temperature sensing circuits utilize either a bridge network or a voltage divider network resulting in an output voltage of from 0-~0 mV dc.
There are a plurality of shortcomings associated with such prior art sensing circuits.
Firs-t, their output signals are so low that they require amplification which introduces gain instability, offset and calibration problems.
Second, conventional circuits require some type of power driver to drive controllers, recorders, meters, digital displays, AjD converters, etc.
Third, circuits incorporating a bridge network require a buffer stage to isolate the bridge network from the output driver.
Fourth, prior art circuits require precision resistors in the bridge network to obtain adequate linearity.
Fifth, transmission problems exist with remote sensing due to the low signal levels that conventional circuits operate with.
.-.
~ 1 ~5~0 Accordingly, it is an object of the present invention to provide a temperature sensing circuit that can overcome the aforementioned shortcomings of the prior art. ~ore specifically, it is an object to provide a circuit that has an output voltage in the range of 0 to approximately 14 volts, so as to overcome amplification and transmission di~ficulties and minimize gain and offset problems.
It is a further object to provide a circuit that can eliminate the necessity for power drivers, buffer stages, and precision resistors, and yet provide adequate linearity.
An additional object is to provide a low cost circuit that is small in size and weight, is composed of off the shelE components, and has high reliability.
Brief Descrlption Of The Drawings Various other objects, features and attendant advantages of the present invention will be more fully appreciated ~rom the following detailed description when considered in connection with the accompanying drawings.
Figure 1 is a schematic diagram of the temperature sensing circuit.
Figure 2 is a schematic diagram of a temperature difference sensing circuit.
Description Of The Preferred Embodiment Referring now to the drawings, and more specifically to Figure 1 thereof, there is shown generally the temperature sensing circuit which is the subject matter of the instant invention. Power supply
Field Of The Invention .
Thls invention relates to temperature sensing circuits, and particularly to such temperature sensing circuits, utilizing a diode sensor.
Description Of The Prior Art Conventional temperature sensing circuits utilize either a bridge network or a voltage divider network resulting in an output voltage of from 0-~0 mV dc.
There are a plurality of shortcomings associated with such prior art sensing circuits.
Firs-t, their output signals are so low that they require amplification which introduces gain instability, offset and calibration problems.
Second, conventional circuits require some type of power driver to drive controllers, recorders, meters, digital displays, AjD converters, etc.
Third, circuits incorporating a bridge network require a buffer stage to isolate the bridge network from the output driver.
Fourth, prior art circuits require precision resistors in the bridge network to obtain adequate linearity.
Fifth, transmission problems exist with remote sensing due to the low signal levels that conventional circuits operate with.
.-.
~ 1 ~5~0 Accordingly, it is an object of the present invention to provide a temperature sensing circuit that can overcome the aforementioned shortcomings of the prior art. ~ore specifically, it is an object to provide a circuit that has an output voltage in the range of 0 to approximately 14 volts, so as to overcome amplification and transmission di~ficulties and minimize gain and offset problems.
It is a further object to provide a circuit that can eliminate the necessity for power drivers, buffer stages, and precision resistors, and yet provide adequate linearity.
An additional object is to provide a low cost circuit that is small in size and weight, is composed of off the shelE components, and has high reliability.
Brief Descrlption Of The Drawings Various other objects, features and attendant advantages of the present invention will be more fully appreciated ~rom the following detailed description when considered in connection with the accompanying drawings.
Figure 1 is a schematic diagram of the temperature sensing circuit.
Figure 2 is a schematic diagram of a temperature difference sensing circuit.
Description Of The Preferred Embodiment Referring now to the drawings, and more specifically to Figure 1 thereof, there is shown generally the temperature sensing circuit which is the subject matter of the instant invention. Power supply
2 includes a voltage regulator diode, CRl, which provides a reference voltage of 6.2 volts at the input terminals of operational amplifier ARl. Series dropping resistor Rl has a value of 7.87K ohms. Capacitor Cl I ~ 65 ~ ~ ~
is utilized to filter any unwanted signals that may be generated by zener diode CRl. Capacitor C2 filters any unwanted signals that may interfere with the sensing diode CR2.
Operational amplifier AR2, operates as an emitter follower that reduces the load on operational amplifier ARl, so that power supply 2 is more stable, thus assuring circuit stability. Since the input impedance of operational amplifier AR2 is very high, it enables operational amplifier ARl to drive more of a load. Except when driving higher loads, the power supply works equally well when amplifier AR2 is replaced with a straight wire from the output of amplifier ARl to resistor R4. The power supply output voltage, Vl, is a function of the ratio of R4 to R2.
If R2 were 10K ohms and R4 were lK ohms, then the gain of operational amplifier AR1 would be .l and the voltage at Vl would be -.62 volts. This voltage will forward bias diode CR2, and since the voltage is less than the cutoff voltage (.7 volts) for CR2, diode CR2 has some value of characteristic resistance, Rc.
The value of Rc changes as a function of temperature. As the temperature increases, the diode resistance, Rc decreases, causing an increase in the gain of amplifier AR3. Similarly, as the temperature decreases, the diode resistance, Rc, increases, causing a decrease in the gain of amplifier AR3.
The resulting output voltage, Vo, is a linear function of temperature.
Conventional diode sensing circuits utilize constant current biasing techniques so that biasing is accomplished near the point of full conduction. Such circuits have the shortcoming that their point of voltage biasing changes with temperature which introduces non-linearities. The instant invention ~ ~ ~5~
operates in the linear region of the characteristic diode curve at one specific point near cutoff. By utilizing a regulated voltage to establish and maintain a constant bias over the expected temperature range, such non-linearities are eIiminated.
Figure 2 includes a second sensing diode, CR3, identical to CR2, and a resistor R3 so as to comprise a temperature difference sensor. As in Figure 1, CRl provides a power supply reference. A change in temperature causes a change in current through CR2 and CR3. As long as the temperature change for CR2 and CR3 is the same, the output voltage, Vo, is zero volts. However, if the temperature at CR2 is higher than that at CR3, the output voltage, Vo, will be a proportional positive voltage. And correspondin~ly, if the temperature at CR2 is lower than that at CR3, the output voltage Vo, will be a proportional negative voltage. That is the output voltage varies proportionall~
to the temperature difference.
The circuit shown in Figure 2 has a temperature sensitivity greater than 300 mV/C. In either direction, sensitivity varies directly with the identical values of resistors R3 and R5. As the values of resistors R3 and R5 increases, the temperature difference sensitivity will also increase.
Operational amplifiers ARl, AR2 and AR3 are
is utilized to filter any unwanted signals that may be generated by zener diode CRl. Capacitor C2 filters any unwanted signals that may interfere with the sensing diode CR2.
Operational amplifier AR2, operates as an emitter follower that reduces the load on operational amplifier ARl, so that power supply 2 is more stable, thus assuring circuit stability. Since the input impedance of operational amplifier AR2 is very high, it enables operational amplifier ARl to drive more of a load. Except when driving higher loads, the power supply works equally well when amplifier AR2 is replaced with a straight wire from the output of amplifier ARl to resistor R4. The power supply output voltage, Vl, is a function of the ratio of R4 to R2.
If R2 were 10K ohms and R4 were lK ohms, then the gain of operational amplifier AR1 would be .l and the voltage at Vl would be -.62 volts. This voltage will forward bias diode CR2, and since the voltage is less than the cutoff voltage (.7 volts) for CR2, diode CR2 has some value of characteristic resistance, Rc.
The value of Rc changes as a function of temperature. As the temperature increases, the diode resistance, Rc decreases, causing an increase in the gain of amplifier AR3. Similarly, as the temperature decreases, the diode resistance, Rc, increases, causing a decrease in the gain of amplifier AR3.
The resulting output voltage, Vo, is a linear function of temperature.
Conventional diode sensing circuits utilize constant current biasing techniques so that biasing is accomplished near the point of full conduction. Such circuits have the shortcoming that their point of voltage biasing changes with temperature which introduces non-linearities. The instant invention ~ ~ ~5~
operates in the linear region of the characteristic diode curve at one specific point near cutoff. By utilizing a regulated voltage to establish and maintain a constant bias over the expected temperature range, such non-linearities are eIiminated.
Figure 2 includes a second sensing diode, CR3, identical to CR2, and a resistor R3 so as to comprise a temperature difference sensor. As in Figure 1, CRl provides a power supply reference. A change in temperature causes a change in current through CR2 and CR3. As long as the temperature change for CR2 and CR3 is the same, the output voltage, Vo, is zero volts. However, if the temperature at CR2 is higher than that at CR3, the output voltage, Vo, will be a proportional positive voltage. And correspondin~ly, if the temperature at CR2 is lower than that at CR3, the output voltage Vo, will be a proportional negative voltage. That is the output voltage varies proportionall~
to the temperature difference.
The circuit shown in Figure 2 has a temperature sensitivity greater than 300 mV/C. In either direction, sensitivity varies directly with the identical values of resistors R3 and R5. As the values of resistors R3 and R5 increases, the temperature difference sensitivity will also increase.
Operational amplifiers ARl, AR2 and AR3 are
3 of the four operational ampliiers in National Semiconductor Corporation's LM-148. CRl, CR2 and CR3 can be realized by National Semiconductor's lN821, lN91~ and lN914, respectively. Typical values for the resistors and capacitors are shown in Table 1.
- I 1 65~40 COMPONENT VALUE
Rl 7,870 ohms R2 10,000 ohms R3 10,000 ohms R4 1,000 ohms R5 10,000 ohms Cl.1 microfarads at 50 volts C2.1 microfarads at 50 volts While a preferred embodiment of the invention has been shown and described, various other embodiments and modifications thereof will become apparent to persons skilIed in the art, and will fall within the scope of invention as defined in the following claims.
- I 1 65~40 COMPONENT VALUE
Rl 7,870 ohms R2 10,000 ohms R3 10,000 ohms R4 1,000 ohms R5 10,000 ohms Cl.1 microfarads at 50 volts C2.1 microfarads at 50 volts While a preferred embodiment of the invention has been shown and described, various other embodiments and modifications thereof will become apparent to persons skilIed in the art, and will fall within the scope of invention as defined in the following claims.
Claims (7)
1. A temperature sensing circuit comprising:
(a) a power supply producing a stable output voltage;
(b) a temperature sensing element comprised of a diode, said diode having a first end and a second end, said first end being connected to said output voltage of said power supply to forward bias said diode in the linear region of its characteristic curve at one specific point near cutoff to establish a given characteristic resistance for a given temperature, which characteristic resistance varies inversely with changes in temperature; and (c) a current to voltage transducer having at least one input terminal and an output terminal, one of said input terminals being connected to said second end of said temperature sensing element, whereby a voltage appearing at said output terminal is proportional to the temperature which is to be determined by said circuit and sensed by said diode.
(a) a power supply producing a stable output voltage;
(b) a temperature sensing element comprised of a diode, said diode having a first end and a second end, said first end being connected to said output voltage of said power supply to forward bias said diode in the linear region of its characteristic curve at one specific point near cutoff to establish a given characteristic resistance for a given temperature, which characteristic resistance varies inversely with changes in temperature; and (c) a current to voltage transducer having at least one input terminal and an output terminal, one of said input terminals being connected to said second end of said temperature sensing element, whereby a voltage appearing at said output terminal is proportional to the temperature which is to be determined by said circuit and sensed by said diode.
2. The invention of claim 1 wherein said current to voltage transducer further comprises:
(a) an amplifying means having a first and a second input terminal and an output terminal, said first input terminal being connected to said second end of said temperature sensing element, said second input terminal being connected to a ground potential; and (b) a first resistor having a first end and a second end, said first end being connected to said first input terminal of said amplifying means, and said second end being connected to said output terminal of said amplifying means.
(a) an amplifying means having a first and a second input terminal and an output terminal, said first input terminal being connected to said second end of said temperature sensing element, said second input terminal being connected to a ground potential; and (b) a first resistor having a first end and a second end, said first end being connected to said first input terminal of said amplifying means, and said second end being connected to said output terminal of said amplifying means.
3. A temperature difference sensing circuit comprising:
(a) a power supply producing a stable output voltage;
(b) a first temperature sensing element having a first end and a second end, said first end being connected to said output voltage of said power supply;
(c) a second temperature sensing element having a first end and a second end, said first end being connected to said output voltage of said power supply;
(d) a current to voltage transducer having a first input terminal, a second input terminal and an output terminal, said first input terminal being connected to said second end of said first temperature sensing element, said second input terminal being connected to said second end of said second temperature sensing element, and said output terminal having a voltage proportional to the difference in temperature between said first and said second sensing elements; and (e) a first resistor having a first end and a second end, said first end being connected to said second end of said second temperature sensing element and said second end being connected to a ground potential.
(a) a power supply producing a stable output voltage;
(b) a first temperature sensing element having a first end and a second end, said first end being connected to said output voltage of said power supply;
(c) a second temperature sensing element having a first end and a second end, said first end being connected to said output voltage of said power supply;
(d) a current to voltage transducer having a first input terminal, a second input terminal and an output terminal, said first input terminal being connected to said second end of said first temperature sensing element, said second input terminal being connected to said second end of said second temperature sensing element, and said output terminal having a voltage proportional to the difference in temperature between said first and said second sensing elements; and (e) a first resistor having a first end and a second end, said first end being connected to said second end of said second temperature sensing element and said second end being connected to a ground potential.
4. The invention of claim 3, wherein said supply being connected to an input reference voltage further comprises:
(a) a second resistor having a first and second end, said first end being connected to said input reference voltage;
(b) a regulating diode having its cathode end being connected to said second end of said second resistor, and having its anode end being connected to a ground potential;
(c) a third resistor having a first and a second end, said first end being connected to said second end of said second resistor;
(d) a first amplifying means having two input terminals and an output terminal, said first input terminal being connected to said second end of said third resistor, and said second input terminal being connected to said anode of said regulating diode;
(e) a first capacitor having a first end and a second end, said first end being connected to said end of said second resistor, and having said second end connected to a ground potential;
(f) a feedback loop having a first end and a second end, said first end being connected to said second end of said third resistor and having said second end being connected to said output terminal of said first amplifying means; and (g) a second capacitor having a first and a second end, said first end being connected to said output terminal of said first amplifying means.
(a) a second resistor having a first and second end, said first end being connected to said input reference voltage;
(b) a regulating diode having its cathode end being connected to said second end of said second resistor, and having its anode end being connected to a ground potential;
(c) a third resistor having a first and a second end, said first end being connected to said second end of said second resistor;
(d) a first amplifying means having two input terminals and an output terminal, said first input terminal being connected to said second end of said third resistor, and said second input terminal being connected to said anode of said regulating diode;
(e) a first capacitor having a first end and a second end, said first end being connected to said end of said second resistor, and having said second end connected to a ground potential;
(f) a feedback loop having a first end and a second end, said first end being connected to said second end of said third resistor and having said second end being connected to said output terminal of said first amplifying means; and (g) a second capacitor having a first and a second end, said first end being connected to said output terminal of said first amplifying means.
5. The invention of claim 3 wherein said power supply being connected to an input reference voltage further comprises:
(a) a second resistor having a first and second end, said first end being connected to said input reference voltage;
(b) a regulating diode having its cathode end being connected to said second end of said second resistor, and having its anode end being connected to a ground potential;
(c) a third resistor having a first and a second end, said first end being connected to said second end of said second resistor;
(d) a first amplifying means having two input terminals and an output terminal, said first input terminal being connected to said second end of said third resistor, and said second input terminal being connected to said anode of said regulating diode;
(e) a first capacitor having a first end and a second end, said first end being connected to said second end of said second resistor, and having said second end connected to a ground potential;
(f) a feedback loop comprising:
(i) a fourth resistor having a first end and a second end, said first end being connected to said second end of said third resistor;
(ii) a second amplifying means having two input terminals and an output terminal, said first input terminal thereof being connected to its output terminal, said second input terminal of said second amplifying means being connected to said output terminal of said first amplifying means, and said output terminal of said second amplifying means being connected to said second end of said fourth resistor; and (g) a second capacitor having a first and a second end, said first end being connected to said output terminal of said first amplifying means.
(a) a second resistor having a first and second end, said first end being connected to said input reference voltage;
(b) a regulating diode having its cathode end being connected to said second end of said second resistor, and having its anode end being connected to a ground potential;
(c) a third resistor having a first and a second end, said first end being connected to said second end of said second resistor;
(d) a first amplifying means having two input terminals and an output terminal, said first input terminal being connected to said second end of said third resistor, and said second input terminal being connected to said anode of said regulating diode;
(e) a first capacitor having a first end and a second end, said first end being connected to said second end of said second resistor, and having said second end connected to a ground potential;
(f) a feedback loop comprising:
(i) a fourth resistor having a first end and a second end, said first end being connected to said second end of said third resistor;
(ii) a second amplifying means having two input terminals and an output terminal, said first input terminal thereof being connected to its output terminal, said second input terminal of said second amplifying means being connected to said output terminal of said first amplifying means, and said output terminal of said second amplifying means being connected to said second end of said fourth resistor; and (g) a second capacitor having a first and a second end, said first end being connected to said output terminal of said first amplifying means.
6. The invention of claim 3 wherein said power supply being connected to an input reference voltage further comprises:
(a) a second resistor having a first and second end, said first end being connected to said input reference voltage;
(b) a regulating diode having its cathode end being connected to said second end of said second resistor, and having its anode end being connected to a ground potential;
(c) a third resistor having a first and a second end, said first end being connected to said second end of said second resistor;
(d) a first amplifying means having two input terminals and an output terminal, said first input terminal being connected to said second end of said third resistor, and said second input terminal being connected to said anode of said regulating diode;
(e) a first capacitor having a first end and a second end, said first end being connected to said second end of said second resistor, and having said second end connected to a ground potential;
(f) a feedback loop comprising a fourth resistor having a first end and a second end, said first end being connected to said second end of said third resistor, and said second end being connected to the output terminal of a second amplifying means having said output terminal and two input terminals, a first one of the input terminals of the second amplifying means being connected to the output terminal thereof and the second one of said input terminals of said second amplifying means being connected to the output terminal of said first amplifying means; and (g) a second capacitor having a first and a second end, said first end being connected to said output terminal of said first amplifying means.
(a) a second resistor having a first and second end, said first end being connected to said input reference voltage;
(b) a regulating diode having its cathode end being connected to said second end of said second resistor, and having its anode end being connected to a ground potential;
(c) a third resistor having a first and a second end, said first end being connected to said second end of said second resistor;
(d) a first amplifying means having two input terminals and an output terminal, said first input terminal being connected to said second end of said third resistor, and said second input terminal being connected to said anode of said regulating diode;
(e) a first capacitor having a first end and a second end, said first end being connected to said second end of said second resistor, and having said second end connected to a ground potential;
(f) a feedback loop comprising a fourth resistor having a first end and a second end, said first end being connected to said second end of said third resistor, and said second end being connected to the output terminal of a second amplifying means having said output terminal and two input terminals, a first one of the input terminals of the second amplifying means being connected to the output terminal thereof and the second one of said input terminals of said second amplifying means being connected to the output terminal of said first amplifying means; and (g) a second capacitor having a first and a second end, said first end being connected to said output terminal of said first amplifying means.
7. The invention of claim 3, wherein said current to voltage transducer further comprises:
(a) an amplifying means having a first and a second input terminal and an output terminal, said first input terminal being connected to said second end of said first temperature sensing element, and said second input terminal being connected to said second end of said second temperature sensing element; and (b) a second resistor having a first end and a second end, said first end being connected to said first input terminal of said amplifying means, and said second end being connected to said output terminal of said amplifying means.
(a) an amplifying means having a first and a second input terminal and an output terminal, said first input terminal being connected to said second end of said first temperature sensing element, and said second input terminal being connected to said second end of said second temperature sensing element; and (b) a second resistor having a first end and a second end, said first end being connected to said first input terminal of said amplifying means, and said second end being connected to said output terminal of said amplifying means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000370243A CA1165140A (en) | 1981-02-06 | 1981-02-06 | Temperature sensing circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000370243A CA1165140A (en) | 1981-02-06 | 1981-02-06 | Temperature sensing circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1165140A true CA1165140A (en) | 1984-04-10 |
Family
ID=4119098
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000370243A Expired CA1165140A (en) | 1981-02-06 | 1981-02-06 | Temperature sensing circuit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1165140A (en) |
-
1981
- 1981-02-06 CA CA000370243A patent/CA1165140A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |