SU1578491A1 - Discrete temperature-sensitive resistor level indicator - Google Patents

Abstract

The invention relates to instrumentation and can be used to measure the level of, for example, cryogenic liquids. The device contains N thermistor level sensors 1, N capacitors 2, which together with sensors form differentiating circuits 3, pulse generator 4, N-1 elements AND 5, logic circuit 6, consisting of N channels, each of which contains a single vibrator 7 and D- trigger 8. The outputs of the logic circuit are connected to the N-channel indicator 9. In the steady state operation, the LED lights up corresponding to the liquid level in the tank, while all sensors that are below the liquid level, except the top one, are disconnected from the generator. 1 hp f-ly, 2 ill.

Description

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figure 1

This invention relates to instrument making and can be used in various industries to measure the level of predominantly cryogenic liquids.

The purpose of the invention is to increase the efficiency of the device by reducing the power dissipated in a controlled environment.

FIG. 1 shows a block diagram of the device; in fig. 2 - stress diagrams.

The device contains n level 1 sensors (1.1L 1.2 1.p) installed evenly along the height of the monitored capacitance, n capacitors 2 (2.1, 2.2, .., 2.p), which together with the level 1 sensors form differentiating circuits 3 (3.1 , 3.2, ..., Z.p), a generator of 4 pulses, n-1 elements AND 5 (5.1, 5.2, .... 5. (n-1)), logic circuit 6, consisting of n channels 6.1 , 6.2b. P., Each of which contains a single vibrator 7 and a D-flip-flop 8, the inverse output of which is the channel output, the input of the single vibrator 7 is the channel input, and the output of the single vibrator is connected to the first input of the trigger 8, the second input where d (counting) is an additional input of the logic circuit 6 and the counting input common for all channels. The outputs of the differentiating circuits are connected to the corresponding inputs of the logic circuit 6, the outputs of which are connected to the level indicator 9, and the output of the generator 4 is connected to the auxiliary input of the logic circuit b, to the input of the differentiating circuit Z.p of the upper sensor 1.p level and to the first inputs of the And elements (5.1, 5.25. (P-1)), the outputs of which are respectively connected to the inputs of the other differentiating circuits 3.1, 3.23. (N-1), a

the second inputs of the elements And 5,1,5.25. (p-1)

respectively connected to the outputs of the channels of the logic circuit b corresponding to the sensor of the upper level, i.e. the output of channel 6.2, etc., is connected to the first input of element 5.1; and the output of channel 5 is connected to the first input of element 5. (p-1) - the output of the channel bp

The level indicator 9 may, for example, consist of n identical channels, each of which contains a series-connected buffer driver 10, an LED 11 and a resistor 12 connected by a second output to a positive polarity power source (not shown), and the inputs of the buffer driver 10 The inputs of level 9 indicator.

The device works as follows.

When power is applied to the level gauge at time ti (Fig. 2), the flip-flops 8 are reset to the zero state (the reset device is not shown) and the generator 4 begins to generate square pulses with a duration of tu (Figure 2, Ui) arriving

through the first inputs of elements And 5.1, 5.2

5. (p-1) due to the high voltage levels present at their second inputs (log level 1), to the inputs of differentiating circuits 3.1, 3.2 3. (p-1) and

directly to the differentiating circuit Z. p. It is obvious that the pulse passing through the differentiating chain changes its shape depending on the value of the time constant of the chain

,

where R is the resistance of sensor 1 level; C - capacitor 2 capacitance. The required pulse shape at the output of the differentiating circuit can be

get, choose its time constant according to the ratio

J

Since in reality the parasitic elements of the RC circuit as well as the impedance of the source RU of the input signal affect the output voltage of the differentiating circuit, in order to jump the input voltage Um at the output of the differentiating circuit, the voltage

U / Vx -tp out (1) - tch-T-R- e

 C (RU + R). 0) Ru + R D

5 Thus, the maximum value of the output voltage level depends on the ratio between the resistances R and RU and with a significant decrease in the value of resistance R the level of the output voltage

The Q voltage also decreases. In addition, due to the final length of the front of the input voltage, due to the influence of the parasitic output capacitance of the generator and the parasitic capacitances of the differentiating circuit and cable, the length of the leading front of the output pulses increases, which also leads to a decrease in amplitude.

Differential circuit parameters

Q is chosen in such a way that when the level sensors in the refrigerant, when the value of their resistances is maximal, the time constants of the circuits are respectively

5ri "r2 ..." rn "ktu.

If the level sensors are located outside the cryogenic liquid, for example, when they exit from the refrigerant, or its absence in the tank where the sensors are installed, their resistance is minimal, which significantly reduces the time constant of the differentiating circuits 3. If the value of

k 0.1-0.3

tu

for the level 1 sensors located in the refrigerant, when their resistance is maximal, it is obvious that when the level sensors exit from the cryogenic liquid according to formula (1), the output voltage amplitude decreases to almost zero, since the time constant of the differentiating circuits 3 reduced by several orders of magnitude.

Thus, if the refrigerant in the tank, where level sensors are installed, is absent during the ti-ta period (Fig. 2), then the voltage at the outputs of the differentiating circuits 3 is almost zero, and at the outputs of the one-shot 7 logic circuit b low voltage levels (hereinafter - the level of the log. O), while

triggers 6.1, 6.2b.p, gated by

to the falling edge of the pulses, from the output of the generator 4, the levels log are stored at the inverse outputs of logic circuit 6. 1, as a result of which the luminescence of the LEDs 11.1, 11.211.p of the level 9 indicator is absent.

When the refrigerant is poured into the reservoir and the level 1.1 of the sensor 1.1 is immersed, its resistance increases abruptly, the time constant of the differentiating circuit 3.1 also increases and becomes equal to n, as a result of which rectangular pulses are output at its input, different polarity pulses , with a one-shot 7.1 for each pulse of positive polarity (Fig. 2. Ui, U2, Us;) generates a pulse with a duration of tu to T, resulting in the inverse output of the trigger

8.1 Installs and maintains a log level. O, leading to luminescence of the LED 11.1 (fig. 2, Щ; t2-ta). When the level 1.2 sensor 1.2 is flooded, the described processes are repeated for the differentiating circuit 3.2 and the channel

6.2 of logic scheme 6, as a result of which the level O established at the output of channel 6.2 at the time t4 causes the LED 11.2 to glow and

at the second input of the element is And 5.1 level O, which prevents further passage of pulses through the differentiating circuit 3.1 (Fig. 2, t3-t4). When the next pulse arrives at its falling edge, trigger 8.1 overturns and LED 11.1 goes out. In the following, the processes described are repeated for all other

level sensors immersed in the coolant, and the simultaneous illumination of LEDs, for example 11.1 and 11.2. over a period of time ts-t4 T, it is possible to determine the direction of movement of the fluid in a closed tank. The rest of the time, only one LED is lit corresponding to the upper flooded level sensor, i.e. measured liquid level.

When the fluid level decreases, the device works in the same way. Assume that sensors 1.1 and 1.2 are flooded. Here, according to FIG. 2 at the inverse trigger output 8.2 there is a log level. O (ts), prohibiting the flow of pulses from the output of the generator 4 to the differentiating circuit 3.1, and at the second input of the element And 5.2 there is a level log. 1, allowing the flow of pulses to the differentiating circuit 3.2. When the fluid level decreases, the sensor 1.2 at some moment of time appears in its pairs and its resistance drops sharply, thus reducing the time constant of the differentiating circuit 3.2. As a result, the output voltage of the circuit 3.2 decreases almost to zero and on the falling edge of the output pulse of the generator 4, the trigger 8.2 is set to the log state. Oh, while at its inverse output a log level is set. 1, allowing the arrival of pulses from the output of the generator 4 through the element AND 5.1 to the differentiating circuit 3.1, and the LED 11.2 goes out. Since the sensor 1.1 is at this time in the liquid, its resistance is high, alternating voltage is present at the output of the differentiating circuit 3.1 when the next pulse arrives from the output of the generator 4 and the level log is set at the inverse output of the trigger 8.1. O, the firing LED 11.1. When the lower sensor 1.1 comes out of the liquid, its resistance sharply decreases, the level of the log is set at the inverse output of the trigger 8.1. 1 and LED 11.1 goes out.

Introduction to the thermal discrete level gauge n-1 of the elements I, connecting them accordingly to the other elements of the level gauge and the proposed implementation of the logic circuit allows disconnecting from the generator all the level sensors that are below the monitored liquid level, except for one upper level.

Claims (2)

1. Discrete thermistor level gauge containing a pulse generator, N installed along the height of the monitored capacitance level sensors, each of which is connected to the first output of the corresponding capacitor and the corresponding input of the N-channel logic circuit, the outputs of which are connected to the indicator, and the second output of the capacitor connected with the upper sensor, connected to a pulse generator, characterized in that, in order to increase efficiency by reducing the power dissipated in a controlled environment, it has Ticks are made in the form of thermistors, each of which is connected to the common wire by a second terminal, and N-1 elements I are also entered, the outputs of which are connected respectively to the second terminals about B N-1 capacitors, the first inputs to the pulse generator, and the second input of each to the channel output of the logic circuit corresponding to the upstream sensor, with the auxiliary input of each channel of the logic circuit connected to the pulse generator. 2. The level gauge according to claim 1, characterized in that each channel of the logic circuit contains a serially connected one-shot and an O-flip-flop, the counting input of which is an additional input, and the inverse output - the output of the channel.  t