BG110Y1 - Converter with temperature offset for capacitative humidity sensor - Google Patents

Abstract

The converter is used in devices for the measurement and monitoring of the relative humidity of gases, especially of the atmospheric air. It is sensitive and accurate in a wide temperature and humidity range, makes linear convertor, has differential voltage output and simplified electrical circuitry. The converter consists of a multivibrator with two symmetric outputs each having an integration RC-circuit on each of the outputs. The multivibrator is built of two identical transmitors T1 and T2, in the time-setting RC-group of one of them a capacitative sensor for humidity Cx is included, and in the time-setting group of the other one an analogical sensor Ct is connected, the humidity sensitive layer (4) of which is insulated from direct contact with the environment by means of a vacuum applied layer of a precious metal (5), impermeable for the water vapours. (11) 111

Description

The utility model relates to a temperature compensated converter for a capacitive humidity sensor and is used to measure the relative humidity of gaseous media, in particular ambient air over a wide temperature range.

BACKGROUND OF THE INVENTION

Known linear converter capacity - voltage / for small changes in capacity /, which is used in capacitive humidity sensors.

The converter contains a multivibrator with two symmetrical outputs and one integrating CS circuit K, C _p resp. K ₂ C ₂ for each of the outputs, made up of two identical transistors T _p or T _{2, the} capacitor C ₃ of the setting group consisting of resistor K ₃ and the capacitor C ₃ , the second transistor T ₂ is a capacitive humidity sensor, the setting group of the first transistor T ₁ is constructed of resistor K ₄ and capacitor C ₄ , the capacitor C ₄ being a temperature-stable supporting capacitor with a capacity equal to the capacity of the sensor in the dry state. The thermal stabilization of the circuit is achieved by the selection of transistors with the same characteristics and temperature-stable resistors with a capacitor C ₄ in the time-setting CS groups.

The disadvantage of the known converter / at its own high temperature stability / is the lack of an element that compensates for the temperature dependence of the dielectric constant of the capacitive humidity sensor, which limits the application of the converter only to sensors with high temperature stability.

TECHNICAL NATURE

The task of the utility model is to introduce in the converter circuit a suitable element that compensates for the temperature dependence of the dielectric constant of the moisture sensitive layer of the sensor, thus expanding the application possibilities.

The problem of the utility model is solved by a temperature compensated converter for a capacitive humidity sensor, which contains a multivibrator with two symmetrical outputs and one integrating CS circuit ^ C, respectively. K ₂ C ₂ , at each of the outputs, constructed by two identical transistors T _p or. T ₂ , the capacitor C ₃ of the timing group consisting of resistor K ₃ and the capacitor C ₃ of the second transistor T ₂ is a capacitive humidity sensor, the timing group of the first transistor consists of resistor K ₄ and capacitor C ₄ , such as the capacitor C ₄ is a sital plate on which are located coplanar comb electrodes, an electrical insulation layer with a polymer layer coated with a chromium-gold metal layer with a thickness greater than 0.1 μ and a layer of M§P ₂ , impervious to water vapor.

The advantage of the utility model is the ability to use in a wide temperature range capacitive sensors with polymer polar dielectric layers, which have high humidity, but a significant temperature dependence of the dielectric constant.

DESCRIPTION OF THE FIGURES Attached

An exemplary embodiment of the utility model is shown in the accompanying drawings, of which: Figure 1 is a thermosensitive compensation element;

Figure 2 is an electrical diagram of the converter.

EXAMPLES FOR THE IMPLEMENTATION OF THE INVENTION

The basis of the thermosensitive element is a rectangular sieve plate 1, on which chromium-gold coplanar comb electrodes 2 and 3 are coated with an insulating layer 4. The polymer layer 5 with the same composition and thickness as used in the humidity sensor is chromium-gold metal layer 6, on which is placed a moisture-proof layer 7 of ΜβΡ ₂ .

APPLICATION OF THE USEFUL MODEL

The action of the heat-sensing element is equivalent to the action of two series-connected capacitors, one of which is formed by the comb-like strip 2 and the metal layer 6 above it, and the other by the comb-strip 3 and its corresponding part from the layer 6. The temperature dependence The capacity is determined by the type of polymer used and the operating frequency.

The converter / figure 2/ consists of a multivibrator formed by the identical transistors T, and T ₂ , the resistors K ₃ = K ₄ , K ₅ = E ₆ , the filter capacitors C ₅ , C ₆ , the tuning capacitor C ₇ , the humidity sensor C ₃ with the wet and temperature dependent capacitance C _x and the temperature sensitive element C ₄ with the temperature dependent capacitance C ₍ . The output integrating circuits of the two transistors are formed by K, and C ,, respectively, K ₂ and C ₂ , with the same values of the elements for the two circuits.K ₇ and K ₈ resistors serve to regulate the output voltage level / at output load of 1 k Ω / The value of the supply voltage is chosen according to the elements of the scheme so that the arithmetic mean / in time / voltage on C ₃ and C ₄ is close to zero, in order to avoid residual polarization of the polymer dielectric layers.

The effect of the converter is as follows. At the same temperature and in the dry state C _x = C ₍ = C _o / due to the same manufacturing technology). The small differences between them are equalized with the tuning capacitor C _? . In this case, rectangular pulses with the amplitude io are obtained on the collector T. and duration T] = 0.7K ₄ Co, respectively at T ₂ 1 ₂ = 0.7 K ₃ Co At K ₃ = K ₄ = K _{o the} multivibrator is symmetric with a fill factor of 0.5 The integrating circuits carry out a creeping averaging of the output voltages of the two transistors with a time constant τ = K ₃ C ₃ = K ₄ C ₄ , which covers / in order k / 10 pieces of output impulses for each of T ₁ and T _2. Points 1 and 2 have potential (by mass).

and, = and - = and / o o '2

K, C + K ₄ C o 4 o and ₂ = to ^K ° ^C ° = and / ₂ 2КС

O 0

In this case, the differential output voltage is i = and - and, = o out 2 1

When the temperature and humidity change, the humidity sensor and the thermostat element change their capacity accordingly to

C = C + AC + AC C, = C + AC,

X O X XV 1 o I as A C _x is the change in capacity at a constant temperature due to moisture adsorption; AC _x , - change of capacity at constant humidity due to change of temperature of capacitive humidity sensor AC, - change of capacity of the thermo-sensitive element at change of temperature. The experimental results show that AC, and AC _x , have the same sign and are of the same order over a wide temperature - humidity range. The quantities C, AC _x , C are in decreasing order, which is why

K, h · * · Gs_ S. „+ <.Se __

_CALL aSay * C * + lShk and »* ₉ {a. + AS * / δSk (y ^m * '(s.ι c ,, _Λ ί. _Χί 4 ^ and _S x-and _4-sGA gkato dC = AC _x , - AC, due to the different physicochemical state of the two sensors (at the same temperature) due to the adsorbed moisture from one of them, depending on the type of polymer used, 0C is on the order of less / or at most much equal to AC _x , as the equality is reached at AC, = 0, corresponding to a temperature stable polymer dielectric layer.

In the particular embodiment of the converter with elements T, T ₂ , 2T3705D, Κ = Κ = Κ = Κ ₆ = 500Ω; K = K = 40 _w ± 1%

C, = C ₂ = C ₅ = C ₆ -20 nE at output load ΗΩ and after trimmer potentiometer adjustment Κ _? = 2 ^ Ω is obtained and _ref = 0 + -100 mU for the entire humidity range, where ACx = JurP. The temperature dependence is up to 0.1% relative humidity at 1 ° C.

The differential output voltage is convenient for secondary conversion with an operational amplifier, which brings it to standard values relative to mass.

Claims (1)

Temperature compensated converter for capacitive humidity sensor, which contains a multivibrator with two symmetric outputs and one integrating CS circuit at each output, made up of two 10 identical transistors, a capacitor of a setpoint group consisting of a resistor and a capacitor, a capacitor is a capacitive humidity sensor, the timing group of the first transistor consists of a resistor and a capacitor, characterized in that the capacitor (C ₄ ) is a sieve plate (1) on which there are coplanar comb electrodes (2 and 3) which are coated with an insulating layer (4) and a polymer layer (5) coated with a chromium-gold metal layer (6) with a thickness greater than 0, 1 μτη, and layer / 7 / of ΜβΡ ₂ , impermeable to water vapor.