JPS592080B2 - Nisenshikisitsudohatsushinki - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-wire humidity transmitter that transmits the humidity status at a slave station to a master station.

An object of the present invention is to provide a two-wire humidity transmitter in which humidity detection in a slave station is configured to compensate for the influence of temperature atmosphere on the slave station and transmitted to a master station.

Relative humidity depends on temperature, and exhibits different values depending on temperature, as shown in FIG. 5, for example. Conventionally, a five-wire or four-wire transmission line is used to measure humidity and temperature at a slave station. and transmits signals to the master station. However, when there are a large number of slave stations and the signal line is interpolated along with other signal lines into piping installed during construction, it is not only uneconomical to have a large number of transmission lines. Needless to say, it is time-consuming. The present invention simultaneously transmits the humidity and temperature conditions at the slave station to the master station using two transmission lines, and without providing a power supply to each slave station.
It is installed only in the master station, and gives electric power to the slave stations from the master station.
By retrieving and calculating at the master station the amount of change in the electrical force that occurs in response to changes in the state at the slave station,
It is configured to obtain a true relative humidity value that is independent of relative humidity temperature.

In FIG. 1, a master station 10 is provided in a central monitoring section and is connected to a slave station 20 by two transmission lines rl and 2. In the master station 10, switches 51 and 52 are connected to the constant voltage power supply E.
The electric force is switched by a flip-flop circuit or the like so as to alternately apply the electric force to the slave station 20 in the opposite direction, and it is switched from the common terminals Cl and C2 to the terminals al and a2 side and bl and b2 side at equal time intervals. be. Rs is extraction terminal 1
This is a reference resistor connected between 1 and 12. In the slave station 20, a humidity-resistance variable body Rh such as an electrical resistance type humidity detector is used.
and a temperature-resistance variable body Rt such as a thermistor or a linear rice resistor are connected in parallel and placed in the same atmosphere. A low-pass filter of a DC blocking capacitor C is connected in series to the humidity/resistance variable body Rh to prevent polarization of the humidity/resistance variable body. A capacitor C is inserted to prevent the temperature-resistance variable body Rh from polarizing due to the offset voltage that occurs when switching the power supply, and from accumulating charges and deteriorating the sensor. A rectifying element such as a diode D is connected in series to the temperature-resistance variable body Rt so as to pass only direct current.

Now, when currents in opposite directions are applied alternately from the power source E at equal time intervals, currents in both directions flow through the humidity/resistance variable body Rh, and current flows in one direction through the temperature/resistance variable body Rt. Now, when the switches Sl and S2 are connected to the terminals Bl and b2, a current flows through the transmission line r1, and a current flows through the humidity-resistance variable body Rh.
No current flows through t.

At this time, an output voltage V appears at both terminals 11 and 12 of the reference resistor Rs in the master station. l can be expressed by the following formula. However, Rh is the resistance value of the humidity-resistance value variable body Rh, and r is the resistance value of each of the transmission lines Rl and r2, which are both equal.

Other symbols also indicate their respective values. Note (1)
In order to establish the formula, it is assumed that the relationship Rh》Rs》2r is satisfied.

The resistance value of the humidity-resistance value variable body Rh usually changes with changes in humidity within the range of 50 kilohms to about 1 tag ohm, but the resistance value of the reference resistor Rs is about 200 ohms, and the transmission line resistance r is 10 ohms. That's about it.

The humidity-resistance value changing body Rh is shown as a logarithmic function of relative humidity (%) as shown in Figure 5, and this value takes temperature as a parameter, and as the temperature rises, the resistance value changes at the same relative humidity. has a low value. As shown in Figure 6, when the reciprocal of the resistance Rh (Qh) is plotted on the vertical axis, the value Qh
is approximately proportional to relative humidity. Further, if the temperature rises, the value Qh also changes, and this ratio is approximately proportional to the temperature rise, as shown in FIG. Here, the value R
If we replace h with its reciprocal Qh in equation (1), the value Qh becomes the standard admittance Qhs at the temperature dependence and standard humidity.
Since there is, it is further shown as the following formula.

On the other hand, if the switches Sl and S2 are switched to the terminals Al and a2, the current will flow in the opposite direction, and if current 1 flows through the transmission lines Rl and r2 and current 11 flows through the humidity-resistance value changing body Rh, then the temperature resistance value changing body l-11 flows through Rt.

At this time, the following formula holds true.

However, Vd is the forward voltage of diode D. However, the impedance Rc of capacitor C is f-10H.
If z1C-500μF, then z-±)
−2πFcl. 5 kiloohm, Rh>l
>Rc and can be ignored.

Equation (5) can be converted into the following equation.

Substituting equation (6) into equation (4), the output voltage 02 appearing across the reference resistor Rs at this time is expressed by the following equation.

However, it is possible to set 2r<Rs x Rt x Rh.

Here, Rt is a logarithmic function of temperature as shown in Fig. 8, and as shown in Fig. 9, Qt is the reciprocal of temperature - variable resistor Rt.
If it can be assumed that there is a proportional relationship to temperature for the reason described later, the following equation holds true. Also, the value Qt is the standard admittance Qts VO2-1: (E-Vd)Rs-Qt=(E-Vd)R
s(△Qt+Qts)2(E-Vd)Rs・△Qt+(
E-Vd) Rs-Qts...(V) Now, for example, the resistance value Rt of a thermistor is a logarithmic function of temperature.If you insert a series resistance into this thermistor and use the reciprocal of both, that is, Qt, the temperature It can be expressed as a linear proportional function.

According to the above, the polarity of the constant voltage power supply E is alternately reversed at a constant frequency, and as shown in FIG. 2, the output voltage VO1VO2 has a peak value with respect to zero and appears at both ends of the reference resistor Rs.

When formula (3) is multiplied by K by an appropriate constant K, K-E-
When the condition Rs.ΔQt2=(E-Vd)Rs.ΔQt is satisfied, the following equation is obtained by subtracting the (self) equation and the (own) equation.

However, △H is the relative humidity, c is a constant, and K is a coefficient.The result of the formula uses a temperature-dependent humidity sensor, and the temperature sensor is used as a medium, and the output o is proportional to the true relative humidity that is independent of temperature. This is something that can be obtained.

FIG. 4 shows a specific circuit diagram of an embodiment of the present invention.

The upper circuit in Figure 4 is a circuit that switches the polarity of the voltage supplied to the slave stations in the master station, and the lower circuit converts the output VO appearing across the reference resistor Rs to the true humidity independent of temperature. Proportional output voltage V. This is a circuit to obtain 3.

Each glasso of A, B, C, D, E in FIG. 3 corresponds to A, B. in FIG. 4. It shows the voltage values at points C, D, and E, and point A shows the result of formula (self) as the value obtained by multiplying the output voltage generated in the humidity-resistance variable body Rh by K through the amplifier. It is.

Point B is the voltage V generated across the temperature-resistance variable body Rt. 2, and point C and D are the smoothed values at points A and B, and point E is the result of the subtraction operation of the output at point C and D.
The voltage V shown by the formula.

Appears as 3.

As described above, the present invention is capable of obtaining a true relative humidity value independent of humidity using two wires, and only requires two transmission lines, and there is no need to provide a power source on the slave station side. The economic benefits that can be gained from this are extremely large.

[Brief explanation of drawings]

The figures show an embodiment of the present invention, Fig. 1 is a circuit connection diagram for explaining the principle, Fig. 4 is a concrete circuit connection diagram, Figs. 2 and 3 are output voltage characteristic diagrams, and Fig. 5 is a circuit connection diagram for explaining the principle. Graph showing the relationship between relative humidity %Rh and resistance value Rh of the temperature-resistance value changing body, No. 6
The figure is a graph showing the relationship between the reciprocal Qh of the resistance value Rh and the relative humidity %Rh in different temperature conditions. Figure 7 is a graph showing the relationship between the reciprocal Qh and the temperature °C. Figure 8 is the change in temperature vs. resistance value. Graph showing the relationship between body resistance value Rt and temperature °C, No. 9
The figure is a graph showing the relationship between the reciprocal Qt of the resistance value Rt and temperature. 10... Master station, 20... Slave station, Rh.
...Humidity - resistance value changing body, Rt...temperature - resistance value changing body, Rs ......standard resistance, Sl, S
2... Changeover switch, F... flipflop circuit.

Claims (1)

[Claims] 1 In the slave station, a series-connected humidity-resistance variable body and a low-pass filter are connected in parallel to a series-connected temperature-resistance variable body and a diode, and the master station connects a power source and a voltage source that change the polarity to provide voltage. It has a reference resistor connected in series with the power supply, and voltages in opposite directions are alternately applied from the master station to the slave stations connected in parallel to the two transmission lines via the two transmission lines. At the master station, the two-wire humidity system obtains temperature-independent relative humidity by subtracting the relative humidity and temperature-dependent voltage generated across the reference resistor and the temperature-dependent voltage. Measurement transmission equipment.