JPS58191926A - Detecting apparatus of liquid level - Google Patents

Abstract

PURPOSE:To detect a liquid level and to increase the reliability by impressing a voltage through a fixed resistance to thermosensitive resistance elements of series connection in an air and a liquid vessel respectively and comparing the voltage at the connection point of the thermosensitive resistance element with the reference voltage. CONSTITUTION:The thermosensitive resistance element Rs1 for detecting the surrounding temp. and the thermosensitive resistance element Rs2 for detecting whether a liquid 2 in a tank 1 exists up to a prescribed level or not are connected in series. And the voltage Vcc selected at the suitable value is impressed through the resistance R0 to prevent the unstable detection due to the self- heating with supplying the constant electric power to the elements Rs1, Rs2 even if the surrounding temp. is varied. It is constituted so that the difference between the voltage V1 at the connection point and the reference voltage V2 is detected by an operational amplifier 3. Thereby, it is possible to increase the output of the amplifier 3 to the high level when the element Rs2 is in the liquid 2 and to decrease the output to 0-level when the liquid level descends lower than H.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a liquid level detection device for detecting whether a liquid in a container such as a liquid supply tank, for example, a W image agent such as a copier, ink of an inkjet printing device, etc. is at the specified level or not. In particular, by self-heating the temperature-sensitive resistance element and detecting changes in resistance due to differences in heat dissipation, it is possible to detect liquid levels that are stable against fluctuations in ambient temperature 1W, are small, and are reliable over time. The present invention aims to provide a detection device.

Conventionally, liquid level detection in a container involves a combination of a float with a magnet and a reed switch, or an optical detection method using light transmittance, but the float method In order to obtain buoyancy, the size of the float becomes large, and the material of the float may be limited due to the problem of contact with liquid. Furthermore, with optical detection, it is difficult to ensure sufficient reliability over time.

The present invention has been made in view of the above circumstances, and is capable of self-heating a temperature-sensitive resistance element and detecting a change in heat dissipation based on the difference in heat dissipation depending on whether or not the temperature-sensitive resistance element is in a liquid. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a liquid level detection device 1t of the present invention in which a temperature-sensitive resistance element is mounted in a tank, where 1 is a tank, 2 is a liquid, and R5 is a temperature sensor for detecting ambient temperature. The resistance element R82 is a temperature-sensitive resistance element that detects whether the liquid is at a predetermined level or not. Voltage is applied to each resistance element from the power supply to self-heat, which reduces heat dissipation in the liquid and air. Depending on the difference, the values of Rst and R52 are different, and it is thereby detected whether the liquid is at a predetermined level or not. In other words, when the liquid level becomes below H in Figure 1, R8I
and the heat release rating of R82 (1! are equal, Rst - R8
2 and outputs an output signal indicating that the liquid level has fallen below a predetermined level.

FIG. 2 is a diagram showing a liquid level detection circuit incorporating Rst XR52 of FIG. 1, where Rsl and R82 have negative analytical resistance characteristics. When the liquid level is above H and R32 is in the liquid, even if it is self-heated by the supplied power, it dissipates more heat than R8+ in the air, and the resistance value decreases less, so Rst < R82. be. So the resistance R+, R2
If the (direction is made equal, (voltage V+ at the connection point of Rst and R82) '(voltage V2 at the connection point of R+ and R2)
), and when Vl is applied to the non-inverting input terminal r of the operational amplifier 3 and V2 is applied to the inverting input terminal, the output ij of the operational amplifier becomes High level. When the liquid level is one degree lower than H and the heat dissipation of R8I and R8□ becomes equal, R3l-R82 becomes R3l-R82, and therefore Vl-:v2, so the output of the operational amplifier 3 shows 0 level. Here, if the ambient temperature of the tank 1 in Fig. 1 fluctuates in the β range of 5°C to 50°C, the temperature-sensitive resistance elements R8I and R8□ will also fluctuate by this amount, and for example, in a state where they are not self-heating, 5℃
RS□-2R8□=12Ω, R31-R8 at 50℃
Change Ω to □-2. Therefore, if the applied voltage is constant in response to fluctuations in the height of the plant, the power consumption of the temperature sensing element will fluctuate greatly, causing abnormal self-heating and making stable detection impossible. It is desirable to use an applied voltage method in which the power consumed remains constant even if the ambient temperature fluctuates.

Even if the ambient temperature fluctuates, one temperature-sensitive resistor
Assume that a constant mW power is supplied. 12Ω at 5℃, 5
At 0℃ and 2Ω, 5mW is constant, so fd, )
VO in FIG. 2 should be 6.3 V at 155cm and 5+1'' at 5°C, respectively.The voltage Vcc applied to the resistor Ro1 that satisfies this is 21X+.

---"'--Vcc2: 155 RO+ 2.1 x] (determined from 1, in this case Vcc = 22 V, R
It becomes O-1nKΩ. In this way, the power supply voltage, resistance R
If O is set, a constant power is supplied to the temperature sensitive resistor element -r- even if the ambient temperature fluctuates, and stable level detection can be performed without abnormal self-heating. In addition, ↑1 ball anti-RI,
The setting of R2 may be R12R2->Rs=R52, and in this embodiment, stable detection is possible with a value of Ω of 200 to 333.

In order to increase the t1 detection degree to -F in the third section, the supply tL force is increased by 2.
The f+pi output circuit is shown when Vcc is set to a high voltage value such that 0 mW is generated, and the same reference numerals as in FIG. 2 represent the same meanings.

Supply, 1. : When 11- is quotient, especially when the ambient temperature is high, the resistance value becomes extremely small due to self υ Put it away. Therefore, in order to prevent runaway due to this self-heating, the supply voltage application time is limited to the third case, and the monostable circuit 4 is turned on by the detection start signal, and its output is The transistor 5 is turned on for a fixed time 1:i1, and the power supply voltage cc2 is applied to the detection element for a fixed time, and detection is performed in the same manner as in the case of FIG. Since the power supply voltage is applied only for a limited period of time, runaway due to self-heating will not occur even if a high electrical ratio is applied to increase detection and sensitivity.

As described above, according to the present invention, by utilizing heat dissipation during self-heating of the temperature-sensitive resistance element, the liquid gap detection is small, reliable over time, and stable even when the ambient temperature fluctuates. It can be performed.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration when the temperature-sensitive resistance element of the liquid level detection device according to the present invention is mounted in a tank, and FIG. FIG. 3, 1/11, showing the configuration is a circuit configuration diagram of the liquid level detecting device according to the present invention when the power supply 'aL coining coining open time is determined. 1. Tank, 2.Liquid, R8I, R82.1 resistance element, Ro

Claims (3)

[Claims] (1) A voltage is applied via a fixed resistor to two series-connected temperature-sensitive resistance elements, one in the air and the other in a liquid container, and the voltage at the connection point of the temperature-sensitive resistance elements is A liquid level detection device that detects the liquid level by comparing reference voltages. (2) Claim (1) wherein two series-connected fixed resistors are connected in parallel to the two temperature-sensitive resistance elements, and the voltage at the connection point of the two fixed resistors is the reference voltage. The liquid level detection device described in . (3) The liquid level detection device according to claim (m), wherein the application of the voltage is limited to a certain period of time.