HU185235B - Temperature-compensated electric signal transducer for measuring humidity - Google Patents

Abstract

Electric humidity transmitter with temperature compensation. Field of application is analytical metrology. In the electric humidity sensor according to the invention, the influence of the temperature of the measurement object on the moisture measurement value is compensated without errors, without having to use a temperature measuring element with its known disadvantages. This is accomplished by using one or more dielectric moisture sensing elements in the chain of a phase shifter oscillator. This creates a moisture-dependent frequency-analogue electrical signal in the oscillator. When the temperature of the measured object changes, its reactive and reactive resistance change in the same direction. This same-sense effect of the temperature on these two types of resistance is converted in the phase shifter oscillator in an opposite effect on the oscillator frequency.

Description

Field of the Invention

The present invention relates to the field of analytical measurement technology. Above all, it is suitable for measuring the moisture content of air and other gases as well as solids and liquids.

Characterization of familiar technical solutions

Electrical encoders for measuring humidity are known and provide an electrical signal proportional to or equivalent to the humidity of the object being measured. Since the temperature of the object to be measured substantially falsifies the electrical signal that informs about the moisture content, in known encoders for measuring moisture, this influence of the temperature of the object to be measured is eliminated by arranging a temperature measuring element along with the humidity measuring element. can be properly linked. These known electric encoders have the disadvantage that the temperature effects which interfere with the humidity measurement can be eliminated only within certain error limits, since the required temperature measuring element does not allow the determination of the temperature of the signal required for the moisture content. The reason for this is that the temperature measuring element is separated from the humidity measurement location, the element is characterized by a certain inertia, it is heated by its own measuring current and the element gets older over time.

Object of the invention

In the electric encoder for humidity measurement according to the invention, the above-mentioned disadvantages are to be eliminated, and the disturbing temperature effects are to be compensated for without the need for a separate temperature measuring element.

Summary of the Invention

The humidity transducer of the present invention consists of one or more humidity sensing elements that are incorporated as frequency determining members into a phase shift oscillator resistor capacity chain. In this way, the transmitter delivers a frequency-dependent electrical signal that depends on the moisture content. For measuring the moisture content of gases, the moisture meter is a moisture resistance electrical resistance which is applied as a very thin layer to a substrate. This thin layer of resistance communicates with the water vapor content of the surrounding gas by absorbing water from the gas at increasing humidity and vice versa. This water flow (metabolism) causes a change in the concentration of charge carriers in the resistor. In these cases, at generally limited concentration values, the charge carriers bind very strongly to the solid interface of the resistor layer, and therefore interface polarization occurs. Consequently, changes in the moisture content of the gas in the environment primarily affect the resistivity of the resistance layer. As the temperature changes, the heat exchange (energy exchange) between the gas and the clenalisation layer takes place. This changes only the mobility of the charge carriers in the resistor layer. As a result of temperature declines,. the active resistance of the resistor layer and the resistance of the barrier change in the same direction. Both the moisture content and the temperature affect the state of the same measuring element at the same time, thus affecting the resistance layer. In a phase shift oscillator with a resistance and capacitance chain, its own frequency is decisively determined by the value of its members. If the resistor layer described above, which is simultaneously capable of sensing temperature and humidity, is a member of the phase shift oscillator circuit, the active and reactive resistance of the resistor layer affects the oscillator frequency in the opposite sense. The equivalent effect of temperature on the ipus value of the two resistors is converted by the phase shifter oscillator to the opposite effect on the oscillator frequency. In this way, the effect of temperature will in principle be compensated. By properly selecting R and C values in the phase shift chain, full compensation can be assured. By replacing the measuring capacitors in the phase shift oscillator capacitance and resistance circuit with elements suitable for measuring the moisture content, where solids can be placed in or through the fluids, the transducer is dependent on the moisture content of the solid or the , which, like measuring the moisture content of the gas, is independent of the temperature of the object being measured.

By properly securing the R and C values in the phase shear chain, the temperature compensation of the object being measured is optimally ensured.

Execution example

An electric transmitter according to the invention for measuring humidity will now be exemplified. Embodiments of the Invention.

Fig. 1 is a schematic diagram of a variant of the transducer according to the invention suitable for measurement in gases, a

Fig. 2 is a transmission characteristic of the encoder of Fig. 1, a

Fig. 3 is a schematic diagram of an electrical encoder for solids and liquids measurement, a

Figure 4 shows the transmission characteristics of the encoder of Figure 3 when measuring the carbon dust in the capacitor space,

Fig. 5 is a transmission characteristic of the transducer of Fig. 3 when measuring a mixture of water-methanol in a condenser space.

Figure I is a dashed box showing the frequency-determining three-membered phase shift chain (RC chain). The chain resistance members are replaced by 2 dielectric humidity sensing elements, which are shown schematically as an assembly of active and reactive resistors. At the 3 inputs, a DC operating voltage is supplied, while at the 4 output, the frequency-dependent electrical analog signal is output. In the transmission characteristic of Fig. 2, the relationship between the output signal (ordinate axis) and the relative air humidity (abscissa) using known humidity measurement elements

185,235 found curves. Each signal represents different temperature values. The points are 20 ° C, the free space 40 ° C, the triangles 60 ° C. The encoder of FIG. 3 shows the following differences from the one shown in FIG. 1;

Phase 1 chain consists of four members. Compared to a three-membered chain, this has the advantage that the oscillator vibrates at lower amplification, which is particularly advantageous at higher frequencies. The phase shift chain is made up of longitudinal resistances and transverse capacities, whereby higher frequencies are obtained relative to longitudinal capacities and transverse resistors. A dielectric measuring capacitor 5 is inserted in place of the capacitor member 1 of the chain, into which a solid or liquid can be placed or flowed.

Here, too, the transducer is composed of reactive and active resistors in a very simplistic manner. * 2

The transmission characteristic of Fig. 4 shows the change in moisture content (abscissa) of the carbon powder prepared for briquetting and the corresponding output signal (ordinate axis) using a scattering capacitor known as a measuring capacitor. The transmission characteristic of the methanol-water mixtures of Figure 5 shows the relationship between the output signal (ordinate axis) and the composition of the mixture (abscissa), using a flow capacitor known as a tendon capacitor.

Claims (1)

A patent claim An electrical temperature transducer for measuring moisture, which is formed by dielectric measuring elements and a phase shift oscillator comprising a phase shifting chain, characterized in that one or more dielectric measuring elements (2,5) are inserted in place of one or more elements of the phase shifting chain (!).