GB2044491A - Automatic control of temperature - Google Patents

Automatic control of temperature Download PDF

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Publication number
GB2044491A
GB2044491A GB8005658A GB8005658A GB2044491A GB 2044491 A GB2044491 A GB 2044491A GB 8005658 A GB8005658 A GB 8005658A GB 8005658 A GB8005658 A GB 8005658A GB 2044491 A GB2044491 A GB 2044491A
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GB
United Kingdom
Prior art keywords
gas sensor
semiconductor gas
operational amplifier
temperature
sensor according
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.)
Withdrawn
Application number
GB8005658A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Draegerwerk AG and Co KGaA
Original Assignee
Draegerwerk AG and Co KGaA
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Draegerwerk AG and Co KGaA filed Critical Draegerwerk AG and Co KGaA
Publication of GB2044491A publication Critical patent/GB2044491A/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G01N27/122—Circuits particularly adapted therefor, e.g. linearising circuits
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/1906—Control of temperature characterised by the use of electric means using an analogue comparing device
    • G05D23/1913—Control of temperature characterised by the use of electric means using an analogue comparing device delivering a series of pulses
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
    • G05D23/24—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element having a resistance varying with temperature, e.g. a thermistor

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Control Of Resistance Heating (AREA)

Abstract

The temperature of a semi-conductor gas sensor 8 (Fig. 1) is controlled by a circuit Fig. 2 including a heater 6 and an NTC temperature sensor 7 in a bridge circuit. The desired temp. is pre-set on a pot 15 and deviation therefrom results in bridge output to an operational amplifier 19. A feedback circuit to the amplifier input including a capacitor 21, causes the amplifier to produce an oscillatory output, eg at 1 KHZ. Thereby a transistor 20 is controlled so as to apply current pulses through heater 6 with a mark/space ratio dependent upon the amount of temperature deviation. <IMAGE>

Description

SPECIFICATION A semiconductor gas sensor This invention relates to a semiconductor gas sensor.
Semiconductor gas sensors allow gas components in gas mixtures, for exampie in the atmosphere, to be monitored and their concentrations to be measured. They demand that a fixed operating temperature, above ambient temperature, be observed in order to produce reliable measurements. To this end, heating means with precise regulation are necessary.
According to the invention there is provided a semiconductor gas sensor provided with electrical heating means and regulating means for the heating means, the regulating means comprising a temperature-dependent resistance arranged for being heated by the heating means, and oscillator circuitry connected with the temperature-dependent resistance for controlling the heating means.
The temperature-dependent resistance is preferably a negative temperature coefficient resistance.
The oscillator circuitry could comprise a capacitor. Also, the oscillator circuitry could comprise an operational amplifier.
A Wheatstone bridge could be provided, the temperature-dependent resistance forming an arm of the Wheatstone bridge. In this case, where the oscillator circuitry comprises an operational amplifier, an inverting input and a non-inverting input of the operational amplifier could be connected with first and second junctions respectively of the Wheatstone bridge. Also, a zener diode could be connected between third and fourth junctions of the Wheatstone bridge, for regulating voltage supplied to the Wheatstone bridge.
Where the oscillator circuitry comprises an operational amplifier, the latter could be arranged for controlling the heating means. In this case, a transistor could be connected between the said output of the operational amplifier and the heating means, for controlling power supplied to the heating means.
The said output of the operational amplifier could be connected with the base of the transistor, and the heating means could be connected with the emitter of the transistor.
Further, where the oscillator circuitry comprises a capacitor, this capacitor could be connected between the emitter of the transistor and the non-inverting input of the operational amplifier.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a view, partly in section, of a semiconductor gas sensor provided with regulated heating means, arranged in a sensor housing, Figure 2 shows a circuit diagram of control circuitry of the regulated heating means and the semiconductor gas sensor shown in Fig.
land Figure 3 shows a diagram of a potential gradient with respect to time at points A and B of the control circuitry shown in Fig. 2.
Referring to Fig. 1, a lower board 2 for electronic components of control circuitry is mounted in a sensor housing 1. The board 2 is supplied with a supply voltage via a supply line 3 from a current supply and indicating device 1 2. An upper board 4 bears a heater 6, which is provided with a resistance layer 5, and a negative temperature coefficient resistance (NTC-resistance) 7 located adjacent to the heater 6 and having a heat-conducting contact therewith but being electrically insulated therefrom. The heater 6 and the NTCresistance 7 are connected via lines to the components on the lower board 2. The object to be heated, a semiconductor gas sensor 8, adjoins the heater 6 in a heat-conducting manner.A measuring line 9, which is connected with the semiconductor gas sensor 8, is conducted together with the supply line 3 out through an aperture 10 in a base 11 of the sensor housing 1, and is connected to the current supply and indicating device 1 2. The sensor housing 1 is sealed with a perforated cover 13, the gas to be monitored being capable of reaching the semiconductor gas sensor 8 from the environment through the perforations of the cover 1 3.
Referring to Fig. 2, the control circuitry includes a temperature-controlled oscillator. A positive supply voltage Us of 10 v is supplied via a protective resistance 14 (800Q) to a Wheatstone bridge which comprises a potentiometer 1 5, a resistance 1 6 (1 2s2), the NTCresistance 7 and a resistance 1 7 (12 Us2). A zener diode 1 8 ensures a constant operating voltage of 5.6 v for the Wheatstone bridge.
The inverting input (-) of an operational amplifier 1 9 is connected with the connecting point of the potentiometer 1 5 with the resistance 16: The non-inverting input (+) of the operational amplifier 1 9 is connected with the connecting point of the NTC-resistance 7 with the resistance 1 7. The output of the operational amplifier 1 9 is connected to the base of a transistor 20, the emitter of which is connected via the heater 6 to the supply voltage Us and, also, via a capacitor 21 (0.15 yF) to the non-inverting input (+) of the operational amplifier 19.
The operation of the control circuitry of the regulated heating means is as follows. The potentiometer 1 5 is set at approximately 1701, corresponding to the desired rated temperature of the heater 6 of 1 50 C, resulting from the operating temperature of the semiconductor gas sensor 8. When the circuitry is put into operation, the heater 6 and NTCresistance 7 are cold and the resistance of the NTC-resistance 7 is high, being approximately 1 2 K52. In this state, the voltage at the noninverting input (+) of the operational amplifier 1 9 (being approximately 2.8 v) is considerably lower than the voltage at the inverting input (-) (being approximately 5.5 v).
The linear range of the operational amplifier 1 9 functioning without negative feedback, with maximum amplification, extends only over a voltage difference between the noninverting input (+) and the inverting input (-) of approximately 0.1 mv. Thus, with the voltage difference present, the operational amplifier 1 9 is fully modulated and its output assumes a lower voltage level. The transistor 20 is thus driven and current flows through the heater 6. Hence, the heater 6 and the NTC-resistance 7 are heated. As a result of this heating, the resistance of the NTC-resistance 7, and hence the voltage difference at the inputs of the operational amplifier 19, is reduced.The voltage level at the output of the operational amplifier 1 9 remains unchanged in the first instance however, since the operational amplifier 1 9 is still fully modulated even with the reduced voltage difference at its inputs. Consequently, heating continues at full power.
Only as the rated temperature (1 50 C) is approached, when the voltage difference at the inputs, at approximately 0.1 mv, comes into the linear range of the operational amplifier 19, does an increase in the voltage level occur at the output of the operational amplifier 1 9. This increase in output voltage produces an oscillating flow of current through the heater 6 in a manner to be described below. Triggering the transistor 20 with a higher voltage level increases its resistance, and the voltage at its emitter is increased.
This positive shift in voltage is fed back via the capacitor 21 to the non-inverting input (+) of the operational amplifier 19, amplified again therein and takes effect at the transistor 20 again. From there, the signal is fed back again to the operational amplifier 19, amplified, and so on.
The result is that the linear range of the operational amplifier 1 9 is passed through rapidly in sudden bursts. The output of the operational amplifier 1 9 assumes an upper voltage level. Referring to Fig. 3, the voltage jump described above is located between points 22 and 23. The transistor 20 now blocks the flow of current through the heater 6, and a pause in heating commences. At this stage, the capacitor 21 is discharged, discharging having taken place in the first instance chiefly via the zener diode 1 8 and the slightly hot resistance of the NTC-resistance 7, until the voltage at a measuring point A is equal to the voltage at the zener diode 1 8 (point 24 in Fig. 3).This discharging occurs rapidly with the time constant: = = C2l.R7hot Additional discharging of the capacitor 21 takes place only via the resistance 17, the resistance value of the resistance 1 7 being higher than the hot resistance of the NTCresistance 7, and lasts longer as a result of the resulting greater time constant (between points 24 and 25 in Fig. 3):: 2 = C21.. R17 If, as a result of the capacitor 21 being discharged, the voltage difference at the inputs of the operational amplifier 1 9 again falls within the linear range of the operational amplifier 19, then the sudden burst-like passage through the linear range described above takes place in the opposite direction (between points 25 and 26 in Fig. 3), the capacitor 21 being fully discharged in sudden bursts. The output of the operational amplifier 1 9 again assumes its lower voltage level, and a flow of current occurs through the heater 6 via the driven transistor 20. Thus, a heating period commences.
A changeover to renewed blocking of current flow through the heater 6 is determined by the charging of the capacitor 21, which takes place via the protective resistance 14 and the hot resistance of the NTC-resistance 7, with the time constant (between points 26 and 22 in Fig. 3): charge = C21 . (R14 + R7hot) If the voltage difference at the inputs of the operational amplifier 1 9 reaches its linear range (at point 22 in Fig. 3), then the oscillating process as described above commences afresh, proceeding at a high frequency (of the order of magnitude of 1 kHz).
Thus, heat regulation is achieved by an oscillating process in which the heater 6 is switched on or off by the temperature-controlled oscillator circuitry described such that the length of a heating period and the pause in heating and also their ratio are dependent on the temperature of the NTC-resistance 7.
When this temperature is lower than the rated temperature, the resistance R7 of the NTCresistance 7 is greater. The heating period, determined by Tcha.ge, is thereby slightly prolonged, since the increase in R7 (to be added to R,4) alters the time constant charge For the fractional pitches of the pause in heating, the increase in the resistance R7 takes effect in various ways.For the first fractional pitch, discharging the capacitor 21 to the voltage of the zener diode 1 8 is prolonged in accordance with the increase in the resistance R7, according to: , = C2,.R7. For the second fractional pitch, the capacitor 21 is discharged further to the voltage prescribed by the voltage divider comprising the NTC resistance 7 and resistance 17, at the connecting point of these components, and this voltage drops due to the increase in the resistance R7. This means that the voltage difference at the inputs of the operational amplifier 1 9 reaches its linear range sooner and, with the sudden burst-like passage through the linear range as described, the pause in heating ends.Since the second fractional pitch occurs with the large time constant: T2 = C21.R17, shortening the second fractional pitch has a considerably more marked effect as far as time is concerned than prolonging the first fractional pitch. In total, this thus results in the pause in heating being shortened.
A temperature which is lower than the rated temperature is therefore counteracted by a slight prolongation of the heating period and a marked shortening of the pause in heating. If a temperature which is higher than the rated temperature is produced because, for example, the sensor housing 1 is transiently subjected to external irradiation, then the processes take place in the opposite direction. A temperature which is higher than the rated temperature is thus counteracted by a slight shortening of the heating period and a marked prolongation of the pause in heating.
If disorders coming to bear from the outside are so great that through the altered resistance value of the NTC-resistance 7 the voltage difference at the inputs of the operational amplifier 1 9 no longer reaches its linear range, then the disorder is counteracted by the heater 6 being continuously on or off accordingly over an extended period, in the same way as described for putting the apparatus into operation, until, as the rated temperature is approached, the oscillating process described commences.

Claims (11)

1. A semiconductor gas sensor provided with electrical heating means and regulating means for the heating means, the regulating means comprising a temperature-dependent resistance arranged for being heated by the heating means, and oscillator circuitry connected with the temperature-dependent resistance for controlling the heating means.
2. A semiconductor gas sensor according to claim 1, wherein the temperature-dependent resistance is a negative temperature coefficient resistance.
3. A semiconductor gas sensor according to claim 1 or 2, wherein the oscillator circuitry comprises a capacitor.
4. A semiconductor gas sensor according to any preceding claim, wherein the oscillator circuitry comprises an operational amplifier.
5. A semiconductor gas sensor according to any preceding claim, provided with a Wheatstone bridge, the temperature-dependent resistance forming an arm of the Wheatstone bridge.
6. A semiconductor gas sensor according to claim 5 as dependent on claim 4, wherein an inverting input and a non-inverting input of the operational amplifier are connected with first and second junctions respectively of the Wheatstone bridge.
7. A semiconductor gas sensor according to claim 6, further conprising a zener diode connected between third and fourth junctions of the Wheatstone bridge, for regulating voltage supplied to the Wheatstone bridge.
8. A semiconductor gas sensor according to any of claims 4 to 7, wherein an output of the operational amplifier is arranged for controlling the heating means.
9. A semiconductor gas sensor according to claim 8, further comprising a transistor connected between the said output of the operational amplifier and the heating means, for controlling power supplied to the heating means.
10. A semiconductor gas sensor according to claim 9, wherein the said output of the operational amplifier is connected with the base of the transistor, and the heating means is connected with the emitter of the transistor
11. A semiconductor gas sensor according to claim 9 or 10 as dependent on claim 3, wherein the capacitor is connected between the emitter of the transistor and the noninverting input of the operational amplifier.
1 2. A semiconductor gas sensor substantially as herein described with reference to the accompanying drawings.
GB8005658A 1979-03-07 1980-02-20 Automatic control of temperature Withdrawn GB2044491A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE2908911 1979-03-07

Publications (1)

Publication Number Publication Date
GB2044491A true GB2044491A (en) 1980-10-15

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GB8005658A Withdrawn GB2044491A (en) 1979-03-07 1980-02-20 Automatic control of temperature

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JP (1) JPS55143435A (en)
FR (1) FR2451029A1 (en)
GB (1) GB2044491A (en)
NL (1) NL7908932A (en)
SE (1) SE7910424L (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0074840A2 (en) * 1981-09-16 1983-03-23 Nordson Corporation Control circuit
WO1987000634A1 (en) * 1985-07-19 1987-01-29 Hoelter Heinz Process for detecting toxic matter in air which enters a cabin o r similar enclosure where persons are present
EP0354486A2 (en) * 1988-08-12 1990-02-14 E.T.R. Elektronik Technologie Rump Gmbh Apparatus for carrying out a method to identify and to quantify unknown gaseous substances
EP0871029A2 (en) * 1997-04-11 1998-10-14 General Motors Corporation Thin film hydrogen sensor
WO2006096804A1 (en) * 2005-03-07 2006-09-14 Sensormatic Electronics Corporation Temperature feedback control for solid state gas sensors

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3431373A1 (en) * 1984-08-25 1986-03-06 Hölter, Heinz, Dipl.-Ing., 4390 Gladbeck Pollutant sensor for motor vehicles, protective working cabins, etc.

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0074840A2 (en) * 1981-09-16 1983-03-23 Nordson Corporation Control circuit
EP0074840A3 (en) * 1981-09-16 1983-04-20 Nordson Corporation Control circuit
WO1987000634A1 (en) * 1985-07-19 1987-01-29 Hoelter Heinz Process for detecting toxic matter in air which enters a cabin o r similar enclosure where persons are present
US4882287A (en) * 1985-07-19 1989-11-21 Heinz Holter Process for indicating the presence of toxic substances in air that is supplied to a personnel-occupied space
EP0354486A2 (en) * 1988-08-12 1990-02-14 E.T.R. Elektronik Technologie Rump Gmbh Apparatus for carrying out a method to identify and to quantify unknown gaseous substances
EP0354486A3 (en) * 1988-08-12 1990-08-01 E.T.R. Elektronik Technologie Rump Gmbh Apparatus for carrying out a method to identify and to quantify unknown gaseous substances
EP0871029A2 (en) * 1997-04-11 1998-10-14 General Motors Corporation Thin film hydrogen sensor
EP0871029A3 (en) * 1997-04-11 1999-02-17 General Motors Corporation Thin film hydrogen sensor
WO2006096804A1 (en) * 2005-03-07 2006-09-14 Sensormatic Electronics Corporation Temperature feedback control for solid state gas sensors

Also Published As

Publication number Publication date
JPS55143435A (en) 1980-11-08
SE7910424L (en) 1980-09-08
FR2451029A1 (en) 1980-10-03
NL7908932A (en) 1980-09-09

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