JPH0252970B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for detecting liquid levels in devices that require various types of liquid level management using a liquid level detection element such as a positive resistance characteristic temperature element or a negative resistance characteristic temperature element. This invention relates to improvements in detection devices.

Conventionally, as a detection element of this type of liquid level detection device,
Using one thermistor, it is installed at the liquid level by detecting the characteristic that the thermistor is self-heated in air due to the difference in heat radiation coefficient between gas and liquid, causing the thermistor temperature to rise rapidly and the thermistor resistance to decrease. The liquid level position was determined by a liquid level detection element.

That is, in Fig. 1, 1 is a transformer, 2
is a rectifier circuit, 3 is a smoothing capacitor, 4 is a stabilizing power supply circuit, 5 is a limiting resistor for preventing excessive current to the liquid level detection element (in this case, a thermistor is taken as an example), 6
is a liquid level detection element composed of a thermistor,
7 is a FET input type operational amplifier having high input impedance. In this figure, an impedance conversion circuit is configured. 8 is a capacitor for holding the output voltage value of the operational amplifier 7 for several seconds or several tens of seconds, and is used as an analog memory for the voltage value for a certain period of time. 9 is a voltage hold circuit that is composed of an operational amplifier 7, a capacitor 8, and a diode, and holds the voltage value while smoothing and correcting it in accordance with the ever-changing temperature state; 12 is a liquid depletion characteristic, a heating characteristic of the thermistor element, and a capacitor; The function of gradually discharging the voltage charged in the capacitor 8, that is, the voltage While forming a discharge path that maintains a predetermined holding voltage in the hold circuit 9, the voltage signal detected by the voltage hold circuit 9 is connected to a resistor 10,
11 is a voltage divider circuit that also has a circuit for voltage division according to the resistance ratio; 13 is the output voltage (potential at point b) of the voltage hold circuit 9 divided by the voltage divider circuit; the direct detection signal voltage from the liquid level detection element 6; This comparator 13 also uses a high input impedance FET input type operational amplifier to hold the voltage value of the capacitor 8 for as long as possible. 14 is an output circuit, and a relay 15 is controlled by a transistor 21 based on a change in the output of the comparator 13.

The operation of the conventional liquid level detection device configured as described above will be explained below with reference to FIGS. 1 and 2.
The configuration of the operational amplifier 7 is called an impedance conversion circuit, and in addition to its practically infinite impedance, a diode is attached, so in terms of an equivalent circuit, the voltage charged in the capacitor 8 is divided by the voltage dividing resistors 10 and 11. It constitutes a discharge circuit. To explain this in terms of the temperature of the liquid, if the voltage value of capacitor 8 is now Vc and the voltage value at point a is Va, then if the liquid temperature is on a downward trend, the Vc value will be Va > Vc.
It continues to charge in the state of , and it always has an upward trend, and when it stabilizes, it is smoothed to the same voltage of Va ₁ = Vc ₁ .

Next, the voltage is maintained in a state where Va<Vc, where the liquid temperature tends to rise, but the resistor 1 of the configuration is relatively high resistance.
After passing through 0 and 11, it is discharged and finally the same voltage value
Va ₂ = Vc ₂ . The voltage at point a in relation to the liquid level detection element 6 is a characteristic of the detection element, and as the temperature increases, the resistance value decreases and Va ₁ >Va ₂ . In FIG. 2, the vertical axis shows the voltage, the horizontal axis shows the time change, the solid line shows the voltage signal that picks out the resistance change of the detection element 6 without time delay, that is, the potential at point a, and the broken line shows the detection element 6 in the normal liquid. The voltage value when the resistance value is high after being immersed and cooled is stored (voltage hold) in the capacitor 8 as an analog voltage value, that is, the potential at point b is shown, and the voltage at point a is determined by the comparator 13 in FIG.
The point potential and b point potential were compared.

In this case, when the detecting element 6 comes out from the liquid into the air, since the detecting element 6 is constituted by a thermistor, it rapidly heats itself, the resistance becomes small, and the potential at point a rapidly decreases. However, the potential at point b is
Since the potential is held in the liquid for several seconds to several tens of seconds, the operation is very slow, so a drop in the liquid level is detected by comparing the potential at point a and the potential at point b using the comparator 13. However, it had the following disadvantages.

First, the liquid level is usually not uniform and may be undulating in some cases, or the normal liquid level is allowed to have some width, and the droplets of the liquid that make up the liquid level may be detected when the liquid level is detected. If it adheres to the element, it may detect that the liquid level is low even though the liquid level is present, give a false alarm about the position of the liquid level, or give a signal that the liquid level is present even though there is no liquid level. It was also possible to take it out. Therefore, the potential at point a of the comparator 13 and the potential at point b
The potential difference between the point potentials is determined by the resistors 10 and 11 of the voltage dividing circuit 12.
was made large by adjusting the point A, so that it would not operate even if there was a slight change in the potential at point a.

However, if the potential at points a and b is set high, when the liquid level detecting element 6 is exposed to the air due to a drop in the liquid level, the resistance will rapidly decrease due to self-heating and the previous state will be maintained. A decrease in the liquid level is determined by detecting a decrease in the potential by comparing it with the potential at point b.
Since the potential difference between the point potential and the point b potential is large, if several seconds to several tens of seconds pass without decreasing below the point b potential, the circuit configuration will inevitably cause the point a potential to change to the potential of the capacitor 8 via the impedance conversion circuit. The liquid level may be changed, that is, lowered, and may return to a balanced state even though the liquid level has fallen, as shown in part c of Figure 2. In other words, due to the circuit configuration, even if it is in the air, the previous state b
If you remember that the point potential is in the air as an analog voltage value, a constant voltage difference will be maintained whether it is on the liquid level or in the air, so liquid level detection will not be possible. For this reason, there was also the disadvantage that it could not be detected even though the liquid level had fallen. That is, a
If the potential difference between point and point b is small, malfunction is likely to occur, and if the voltage difference is large, the liquid level cannot be detected. Also, when the potential difference is increased,
When the liquid level drops and the liquid adheres to the detection element 6 in the form of droplets, the voltage difference is large and the self-heating power of the detection element 6 decreases before the potential at point a reverses the potential at point b. It also had the disadvantage that the potential increased and detection of a drop in the liquid level was delayed.

This invention smoothes and corrects the voltage value generated by the voltage output signal of one liquid level detection element, holds it with a predetermined time constant, and combines this with a divided pressure signal and the voltage signal from the liquid level detection element. By comparing the values with a comparator, counting the number of signal outputs from this comparator, and detecting the liquid level based on this counted value, the liquid level can be determined without fear of malfunction or inoperability even in a wide range of liquid temperature. A detection device is provided.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, the same reference numerals as in FIG. 2 indicate the same or equivalent parts, 15 is an inverter circuit that inverts the output signal of the comparator 13, and 16 is a differentiator circuit that converts the signal change of the inverter circuit 15 into pulses. The signal is input to the counting circuit 18 and a predetermined count is counted by the terminal 18b of the connected output section. 18c
is a terminal for resetting the number of times counted,
Reference numeral 19 denotes a self-holding circuit using an IC 20 and the like based on the output of the counting circuit 18, and this circuit ultimately controls the output relay 15.

Next, the operation will be explained. First, when the liquid level is higher than the liquid level detection element 6, there is a certain potential difference between the potential at point a and the potential at point b shown in FIG. The point potential and the point b potential are reversed, and the pulsed output signal from the differentiating circuit 16 is input to the counting circuit 8 via the comparator 13 and the inverter circuit 15, and after counting a predetermined number of times, the liquid level detection signal is sent to the outside. Put it out.

Therefore, even if the liquid level is undulating, if the normal liquid level is allowed with some width, or if the liquid droplets that make up the liquid level are detected by the liquid level detection element 6.
Even if it sticks to the surface, it will not issue a false alarm because it will be counted and output a predetermined number of times, usually 5 to 6 times. In addition, after counting and operating several times in this way, an alarm is issued for a drop in the liquid level, so there is no risk of false alarms, so the potential difference between the potential at point a and the potential at point b shown in Figure 4 is increased. There is no need to set it, it can be set small, and it is possible to increase the detection sensitivity.As with the conventional system, it consists of one detection element, so it is much easier to use than two thermistors for temperature correction and self-heating. There are no errors caused by changes in characteristics, and the potential difference between point a and point b can be set smaller than before, making it possible to configure a circuit with low power consumption and a very wide liquid temperature range of 0 to 100°C. It is possible to understand changes in liquid level.

In addition, the present invention covers not only the management of the oil level in a compressor as a liquid level, but also equipment that has an oil pan and requires oil level management, a device that detects the liquid level and automatically controls water supply, and It can also be applied to water outage detection circuits.

As described above, according to the present invention, the ever-changing voltage of the voltage output signal of one liquid level detection element is detected and held, the voltage is divided, and this divided pressure value is combined with the voltage signal from the liquid level detection element. is compared using a comparator, the number of signal outputs from this comparator is counted, and the liquid level is detected based on the counted value, so it is highly accurate and can be applied over a wide range of liquid temperatures. There is no risk of malfunction or inoperability, and since only one liquid level detection element is required, the system has advantages such as being compact, lightweight, and inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of a conventional device, FIG. 2 is a voltage change characteristic diagram of voltage signals of each part in FIG. 1, FIG. 3 is a circuit configuration diagram according to an embodiment of the present invention, and FIG. FIG. 4 is a voltage change characteristic diagram of voltage signals at various parts in FIG. 3; In the figure, 6 is a liquid level detection element, 8 is a storage capacitor, 9 is a voltage hold circuit, 12 is a voltage dividing circuit, 1
3 is a comparator, 15 is an inverter circuit, 16 is a differentiation circuit, and 18 is a counting circuit. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 A liquid level that is disposed at a liquid level detection position and whose resistance changes depending on whether or not it is in the liquid, and which generates a voltage signal according to the change in resistance when a predetermined current flows. a detection element, a voltage hold circuit that constantly detects the voltage signal of the liquid level detection element in accordance with the temperature state of the liquid, smoothes and corrects the generated voltage value, and holds it with a predetermined time constant; a voltage divider circuit that forms a discharge path that is involved in the smoothing correction and a predetermined time constant, and divides the voltage signal detected by the voltage hold circuit; It is equipped with a comparator that compares the signal voltage value from the surface detection element and generates an output signal according to the comparison value, and a counting circuit that counts the output signal of this comparator and outputs a signal when a predetermined number of counts has been reached. A liquid level detection device characterized by: