Atmosphere measuring device and flow sensor

• US 5,551,283 A
• Filed: 08/03/1994
• Issued: 09/03/1996
• Est. Priority Date: 08/10/1993
• Status: Expired due to Term

• Current Assignee: Ricoh Elemex Corporation (Ricoh Company Limited)
• Original Assignee: Ricoh Seiki Co. Ltd. (Ricoh Company Limited)
• Inventors: Ishibashi, Tetsuo, Manaka, Junji
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): WIGGINS, JOHN DAVID
• Application Number:
  US08/285,666
• Time in Patent Office: 762 Days
• Field of Search: 73/31.01, 73/29.01, 73/75, 73/204.11, 73/204.14, 73/29.02, 73/24.04, 73/25.04, 340/634
• US Class Current: 73/31.01
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/69 of resistive type
• CPC Class Codes: G01F 1/696 Circuits therefor, e.g. constant-current flow meters
• CPC Class Codes: G01N 27/18 caused by changes in the thermal conductivity of a surrounding material to be tested G01N27/20 takes precedence

Abstract

A low-cost and quick-response type gas-density sensing element is free from positioning error of sensing ambient temperature and gas density and can accurately sense the gas flow even if the environmental conditions sharply change. An output voltage V₁ proportional to an ambient temperature is obtained by heating a sensing element at low temperature and an output voltage V₂ proportional to the ambient temperature and humidity is obtained by heating the sensing element at a high temperature. An output voltage which is proportional to the humidity is obtained by subtracting the voltage value V₁ from the voltage value V₂.

Claims

1. An atmosphere measuring device for sensing presence of a specified gas in an atmosphere according to a change in resistance of a resistor heated in an ambient atmosphere, comprising:

a specified temperature driving circuit for heating the resistor by application of a predetermined first current to the resistor to produce uniform heating along the resistor with a specified temperature increase to a substantial thermal equilibrium whereat the resistance of the resistor is substantially free of influence from said specified gas existing in the atmosphere and is indicative of an ambient temperature;

a high-temperature driving circuit for heating the resistor by application of a predetermined second current to the resistor to produce uniform heating along the resistor with a high temperature increase to a substantial thermal equilibrium whereat the resistance of the resistor varies by the effect of the ambient temperature and the specified gas presence;

a comparator circuit for comparing with each other two voltages generated across the resistor representative of resistances at the high temperature and the low temperature to determine a density of the specified gas contained in the atmosphere from an output voltage of the comparator circuit.

2. An atmosphere measuring device according to claim 1 for measuring density of a specified gas, further comprising:

an ON-OFF signal generating circuit for controlling said specified temperature heating circuit and said high temperature heating circuit to produce a high-temperature and a specified-temperature heating period and a heating-OFF period (pause);

a reference signal generating circuit responsive to said ON-OFF signal generating circuit for heating the resistor in synchronism with the high temperature and the specified temperature heating periods;

a time measuring circuit for determining a timing to read said two voltages representative of the resistance values of the resistor heated to a specified temperature and a high temperature in synchronism with the specified and the high temperature heating cycles;

a voltage measuring circuit for reading the voltages produced by the resistor in synchronism with the timing signal for reading the resistance values of the resistor;

a coefficient setting circuit for setting a coefficient for compensating a voltage produced by the resistor heated to the specified temperature by multiplying it by the coefficient to obtain and output a compensated voltage corresponding to an ambient temperature; and

a memory circuit for storing the compensated voltage and a subtraction circuit for subtracting the memorized compensating voltage from the voltage produced by the resistor heated to the high temperature to determine a density of a specified gas in the atmosphere in proportion to the output of the subtraction circuit.

3. An atmosphere measuring device according to any one of claims 1 and 2, wherein the resistor is a thin heating wire capable of generating heat by applying an electric power thereto, which is formed to a micro-bridge circuit supported at both ends by electro-conducting pins with insulation in an atmosphere to be measured.

4. An atmosphere measuring device according to any one of claims 1 and 2, wherein a heating cycle of the resistor comprises a specified temperature and heating period high temperature heating period for heating the resistor at the specified temperature and the high temperature and a heating-OFF period for allowing a resistance value characteristic of thermal-equilibrium of the resistor to return to at least a resistance value at an ambient temperature.

5. An atmosphere measuring device according to any one of claims 1 and 2, wherein electric power for heating the resistor for the specified temperature heating period and the high temperature heating period is applied in the form of a low-crest pulse of voltage or current and a high-crest pulse of voltage or current to be outputted directly after the low-crest pulse of voltage or current.

6. An atmosphere measuring device according to any one of claims 1 and 2, wherein electric power for heating the resistor for the specified temperature heating period and the high temperature heating period is applied in the form of a saw-tooth voltage or current having a series of triangle-shaped peaks.

7. An atmosphere measuring device for measuring density of a specified gas, comprising:

an atmosphere sensor having a substrate including therein two neighboring cavities of the same size and form and equivalent resistors connected in series to each other and arranged in form of a micro-bridge in the top surface of each of the cavity;

a clock circuit for generating clock pulses for providing a timing to simultaneously drive resistors of the atmosphere sensor;

driving circuit for outputting a low power pulse for inducing small scale heating of one of the resistors and a high power pulse for inducing large scale heating of the other resistor in synchronism with the clock pulse;

means for measuring resistance values of said resistors; and

an arithmetic computation circuit for comparing two resistance values produced in the resistors respectively at a specified temperature and at a high temperature and calculating a density of a specified gas according to the comparison result.

9. A flow measuring device having structure, function and components according the to the density measuring device of claim 7 further comprising:

means for operating said driving circuit in alternating first and second modes;

wherein in said first mode, the said low power pulse is applied to said one resistor while simultaneously said high power pulse is applied to said other resistor;

wherein in said second mode said supply means applies said low power pulse to said other resistor while simultaneously applying said high power pulse to said one resistor; and

wherein said first and second modes alternate in synchronism with the clock pulses from the clock circuit.

8. An atmosphere measuring device for measuring density of a specified gas, comprising:

a substrate including therein two neighboring cavities of the same size and form and equivalent resistors connected in series to each other and arranged in the form of a micro-bridge in the top surface of each of the cavities;

a clock circuit means for generating clock pulses for providing a timing signal to drive said resistors of the atmosphere sensor;

a driving circuit means for outputting a low power pulse for heating one of the resistors to a specified temperature and a high power pulse for heating the other resistor to a high temperature;

the driving circuit means including means for alternately applying one after the other said low power pulse to said one of the resistors and said high power pulse to said other resistor in synchronism with clock pulses from the clock circuit means;

means for determining resistance values of said equivalent resistors while being driven by said low and high power pulses respectively; and

an arithmetic computation circuit for comparing the resistance values produced in the resistors respectively at a specified temperature and at a high temperature and calculating a density of a specified gas according to the comparison result.

10. An atmosphere measuring method whereby a single resistor is inserted in a gas flow to be measured, a small predetermined current substantially unable to noticeably heat the resistor is supplied to the resistor and a resistance thereof is measured, a large predetermined current is subsequently supplied to heat the resistor in a uniform axial manner and a resistance thereof is measured, and a flow rate of gas is determined by subtracting the resistance measured without noticeably heating from the resistance measured with heating uniform heating current by means of detecting voltages generated across the resistor while at substantial thermal equilibrium which are representative of the resistances.

11. An atmosphere measuring method for determining flow of a gas, whereby a single resistor is inserted in a gas flow to be measured, a slowly increasing current is supplied to the resistor, a resistance produced in the resistor at a small predetermined current substantially unable to noticeably heat the resistor and a resistance produced in the resistor at a large predetermined current enough to heat the resistor in a uniform axial manner are measured and a flow rate of the gas is determined by subtracting the resistance measured while said small predetermined current is applied and said resistor is at substantial thermal equilibrium from the resistance measured while said large predetermined current is applied and said resistor is at substantial thermal equilibrium wherein the resistances measured are determined from voltages detected across said resistor.

12. A flow measuring device for determining gas flow, comprising a substrate having a cavity therein, a thin insulation layer formed in the form of a bridge across an upper part of the cavity, a single resistor disposed on the thin insulation layer, means for sensing a resistance value of the resistor by applying thereto a small current or voltage insufficient to cause a heat therein, means for sensing a resistance value of the resistor heated in a uniform axial manner by applying a large current or voltage thereto, means for subtracting the sensed resistance value of the resistor at the small current or voltage from the sensed resistance value of the resistor at the large current or voltage to determine a flow of gas to be measured according to the subtraction result.

13. A flow measuring device according to claim 12, further comprising means for generating a repeatable cycle consisting of a flow measuring period for supplying said small current and subsequently supplying said large current and a pause period for supplying no current, said pause period being longer than a time necessary, for returning a temperature of the resistor to a temperature of gas to be sensed.

14. A flow measuring device according to claim 12, wherein a voltage or a current to be supplied to the resistor for the flow measurement period is a low-crest pulse and a high-crest pulse outputted directly after the low-crest pulse.

15. A flow measuring device according to claim 12, wherein a voltage or current to be applied to the resistor for the flow measuring period is a saw-tooth voltage or current.

16. A flow measuring method for determining gas flow rate, using two resistors inserted in a gas flow to be measured, comprising:

simultaneously applying one of a first current or voltage at a level below that necessary to induce substantive self-heating to one of the two resistors and one of a second current or voltage to the other resistor at a level greater than that of said one of said first current or voltage and sufficient to induce substantive self-heating;

determining resistance values of the two resistors from said one of said first current or voltage and said one of said second current or voltage;

calculating a difference between the two measured resistance values; and

determining a flow rate of the gas flow from the difference of the two resistance values.

19. A flow measuring device according to any one of claims 16 and 18, further comprising:

a clock-pulse generating circuit for generating clock pulses for providing a timing to simultaneously drive said two resistors;

said supply means including a low power pulse generating circuit for applying said one of said first current or voltage to one of the resistors in synchronism with one of said clock pulses; and

said supply means including a high power pulse generating circuit for applying said one of said second current or voltage to the other resistor in synchronism with said one clock pulse.

17. A gas flow measuring device comprising:

a substrate defining a cavity, engraved therein;

an insulation layer formed in the form of a bridge across an upper part of the cavity;

two resistors disposed on the insulation layer;

supply means for simultaneously applying one of a first current or voltage at a level below that necessary to induce substantive self-heating to one of the resistors and one of a second current or voltage to the other resistor at a level greater than that of said one of said first current or voltage and sufficient to induce substantive self-heating;

means for determining resistance values of both of said resistors from said ones of said first and second currents and voltages applied to respective ones of said resistors; and

means for subtracting the one measured resistance value from the other measured resistance value to determine a flow of the gas from a difference of the resistances.

18. A gas flow measuring device for determining gas flow, comprising:

a substrate defining a cavity, engraved therein;

two insulation layers bridged across a top part of the cavity;

two resistors disposed on respective ones of said insulation layers;

supply means for simultaneously applying one of a first current or voltage at a level below that necessary to induce substantive self-heating to one of the resistors and one of a second current or voltage to the other resistor at a level greater than that of said one of said first current or voltage and sufficient to induce substantive self-heating;

means for determining resistance values of both of said resistors from said ones of said first and second currents and voltages applied to respective ones of said resistors; and

means for subtracting the one measured resistance value from the other measured resistance value to determine a flow of the gas from a difference of the resistances.

20. A flow measuring device according to claim 18 further comprising:

means for operating said supply means in alternating first and second modes;

wherein in said first mode said one of said first current or voltage is applied to said one resistor while simultaneously said one of said second current or voltage is applied to said other resistor;

wherein in said second mode said supply means applies said one of said first current or voltage to said other resistor while simultaneously said one of said second current or voltage is applied to said one resistor; and

wherein said first and second modes alternate in synchronism with the clock pulses from the clock circuit.