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
  • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
  • G01N27/223—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity
  • G01N27/225—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity by using hygroscopic materials

Definitions

• the invention relates to an arrangement for determining the relative air humidity by means of a capacitive air humidity sensor and an associated sensor evaluation electronics, the capacitive air humidity sensor having a polymer layer as dielectric and two electrically conductive electrodes.
• air humidity sensors are used for air conditioning systems in buildings, they are usually serviced or replaced regularly. However, if the air humidity sensors are used in air conditioning systems of motor vehicles, they have to function maintenance-free for years if possible under difficult conditions.
• the invention is therefore based on the object of proposing an arrangement for determining the relative atmospheric humidity of the type mentioned at the outset, which works properly without additional maintenance.
• one of the electrically conductive, metallized electrodes is designed as a layered heating resistor with at least two power connections.
• the arrangement according to the invention has the advantage that the capacitive air humidity sensor can be heated up in a simple manner and at any time outside the measuring periods, so that any contamination can be evaporated.
• the electrically conductive electrodes are arranged opposite one another on both sides of the polymer layer or next to one another on one side of the polymer layer.
• the electrodes of the capacitive air humidity sensor consist of platinum, which has a relatively high specific resistance and is therefore particularly suitable in the form of a thin film as a heating resistor.
• another noble metal can also be used.
• the platinum electrode designed as a heating resistor is supplied with current in certain time cycles, it having proven to be advantageous if this takes place each time the arrangement is switched on.
• the heating resistor be briefly energized only when the ambient temperature falls below a predetermined value when the device is switched on.
• a temperature sensor is provided, which is connected to the sensor evaluation electronics and outputs a compensation variable for the determination of the exact relative air humidity by the sensor evaluation electronics.
• a further development of the invention is that the heating resistor is only supplied with current after a predetermined waiting time, which turns out to be has proven to be particularly economical and cost-saving.
• 1 is a side view of an air humidity sensor
• Fig. 3 shows an arrangement for the operation of an air humidity sensor
• the capacitive air humidity sensor 1 shown in FIGS. 1 and 2 essentially consists of a polymer layer 2 as a dielectric and two electrically conductive (metallized) electrodes 3 and 4 located opposite one another Dielectric 2 are also next to each other.
• the electrodes 3 and 4 are provided with power connections 6 and 7, 8, to which feed lines 9 and 11, 12 are connected. Since the electrode 4 is designed according to the invention as a heating resistor, two current connections 7 and 8 are provided for the temporary supply of heating current, while the electrode 3 has only one current connection 6.
• a heating current can be supplied via the two current connections 7 and 8 on the one hand - outside the measuring periods and on the other hand - during the Measuring times - a measuring signal can be removed simultaneously via the current connection 6.
• the capacitive air humidity sensor 1 is used to determine the relative air humidity, the feed lines 9 of the electrodes 3 and 11, 12 of the electrode 4 according to FIG. 3 being connected to a sensor evaluation electronics 13.
• a temperature sensor 14 for determining the ambient temperature via lines 16, 17 is also connected to this sensor evaluation electronics 13.
• An air humidity measurement by capacitance measurement of the capacitive air humidity sensor 1 as well as a temperature measurement by evaluation of the signal supplied by the temperature sensor 14 can thus be carried out in the sensor evaluation electronics 13, which at the same time generates a compensation variable for the determination of the exact relative air humidity .
• the measurement signal for temperature and air humidity can then be removed, which can be displayed by means of a measuring device, not shown in FIG. 3.
• a measuring device not shown in FIG. 3.
• FIG. 4 shows various operating modes of the arrangement according to the invention for heating the capacitive air humidity sensor 1 on the basis of flow charts according to a), b) and c).
• These flow charts can be stored, for example, as a program in a microprocessor 23 of the sensor evaluation electronics.
• the flowchart according to FIG. 4b) differs from the flowchart according to FIG. 4a) only in that before the heating (B) is switched on, a measurement of the ambient temperature T and a comparison with a predetermined temperature value TO (for example +10 ° C.) takes place (F). The heating process is then only initiated if the ambient temperature T falls below the predefined temperature value TO.
• a predetermined temperature value TO for example +10 ° C.
• a component (G) "Wait time has expired?" inserted in addition to the conditions of the flowchart according to FIG. 4a) and FIG. 4b.
• the heating is only switched on when a certain waiting time (e.g. 10 hours) has elapsed. This can also be linked to a predefined temperature value TO.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

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• 1997
  • 1997-07-11 DE DE19729697A patent/DE19729697C1/de not_active Expired - Fee Related
• 1998
  • 1998-06-19 JP JP2000502411A patent/JP2001509600A/ja active Pending
  • 1998-06-19 WO PCT/EP1998/003752 patent/WO1999002980A1/de not_active Application Discontinuation
  • 1998-06-19 EP EP98932176A patent/EP0995110A1/de not_active Ceased
• 1999
  • 1999-06-19 US US09/462,538 patent/US6356087B1/en not_active Expired - Fee Related

Non-Patent Citations (1)

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