JPH04158224A - Level detecting circuit - Google Patents

Abstract

PURPOSE:To enable the prevention of corrosion of electrode rods and also the detection of a number of liquid levels by providing the electrode rods in a plurality and by covering the surface of each of them with a dielectric film. CONSTITUTION:Electrode rods 200 to 207 are provided in the horizontal direction at a prescribed interval from each other so that they project from an insulative base board 11 disposed in the vertical direction, and the surface of each of them is covered with a dielectric film. In the upper end part of a case, a cap part 61 having a hermetically closed chamber formed inside and an impedance detecting part 71 held in the hermetically closed chamber are provided. The electrode rods 200 to 207 are formed of stainless steel rods, while the dielectric film is formed of a resin film about 0.1 mm thick. Based on the input of a pulse signal, a multiplexer 72 selects two adjacent ones of the electrode rods 201 to 207 by a prescribed time in a time sequence and connects them to signal lines L1 and L2 respectively. Accordingly, an impedance detecting circuit 73 detects a liquid level between the two adjacent electrode rods in the time sequence and delivers an output signal V0 thereof to a demultiplexer 74. The demultiplexer 74 is operated synchronously with the multiplexer 72 and distributes the output signal V0 to LEDs 1 to 8 by turns.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a level detection circuit.

[Prior Art] Conventionally, in order to detect the level of a conductive liquid, a predetermined number of electrode rods are suspended from the liquid surface, and a DC voltage is applied between the two electrode rods to detect a change in resistance between the two electrode rods. The liquid level was being detected.

In addition, in order to detect the liquid level of an insulating liquid such as oil, a predetermined number of electrode rods are suspended from the liquid surface, and an AC voltage is applied between the two electrode rods to determine the liquid level by the change in capacitance between them. was detected.

[Problems to be Solved by the Invention] However, the conventional level detection circuit described above has the following problems.

The first problem is that the electrode rods are severely corroded in corrosive liquids or corrosive atmospheres such as strong acids, strong alkalis, and sewage, and require frequent replacement.

The second problem is that when used under strong noise electric fields, noise voltage may be induced between the signal lines coming out of the electrode rod, or the S/N ratio may deteriorate due to an increase in signal line impedance, resulting in false detection. It is a certain thing.

The third problem is that one liquid level can be detected by the change in impedance between a pair of electrodes; in order to detect multiple liquid levels, it is necessary to provide multiple pairs of electrode rods and an impedance detection section equal to the logarithm of the electrode rods. However, if an attempt is made to detect, for example, several tens of levels, the circuit load will become extremely large.

The present invention was made in view of these problems.
The first object is to provide a level detection circuit that can prevent corrosion of electrode rods in corrosive liquids or corrosive atmospheres such as strong acids, strong alkalis, and sewage.

A second object of the present invention is to provide a level detection circuit that can ensure a high SN ratio even under a strong noise electric field.

A third object of the present invention is to provide a level detection circuit capable of detecting a large number of liquid levels with a small circuit load.

[Means for Solving the Problems] The level detection circuit of the first invention includes at least a pair of elongated electrodes arranged at a predetermined position at a predetermined interval in a container containing a fluid to be measured, and the electrodes. The device is characterized by comprising a sealed case to which a base end of the sensor is fixed, and an impedance detection unit housed in the sealed case, the signal input end of which is connected to the electrode, and which detects the impedance between the two electrodes.

The level detection circuit of the second invention includes an elongated insulating base erected at a predetermined position in a container containing a fluid to be measured, and a plurality of detection electrodes arranged longitudinally on the surface of the insulating base. a plurality of signal line sections embedded in the insulating base, one end of which is individually connected to each of the detection electrode sections, and the other end of which extends to one end of the insulating base; It is characterized by comprising a multiplexer that sequentially selects one of the signal voltages, and a detection section that detects the liquid level based on the signal voltage selected by the multiplexer.

A level detection circuit according to a third aspect of the invention includes at least a pair of electrodes each disposed at a predetermined position in a container containing a fluid to be measured, a capacitance detection section that detects a capacitance between the two electrodes, and at least one of the electrodes. and a dielectric film that electrically insulates the fluid from the fluid to be measured.

[Operations and Effects of the Invention] In the level detection circuit of the first invention, the impedance detection section is housed in a sealed case to which the base end of the electrode is fixed.

Therefore, when used under strong noise electric fields, noise voltage may be induced between the signal lines coming out from the electrode rod, or
It is possible to prevent erroneous detection from occurring due to deterioration of the SN ratio due to an increase in signal line impedance.

In addition, since a sealed case is used in this case, the joint between the electrode rod and the signal line connected to it, the connection between the signal line and the terminal of the impedance detection section, and the impedance detection section are protected from moisture. This can prevent insulation failure problems. Furthermore,
If part or all of this sealed case is formed of a conductive metal plate, the influence of external noise can be further prevented by electromagnetic shielding.

The level detection circuit of the second invention covers the surface of each electrode of the electrode pair with a dielectric film to electrically insulate it from the liquid to be measured, and the capacitance between both electrodes when the liquid to be measured is filled between the two electric films. Detect changes. Therefore, when the liquid to be measured is conductive, the capacitance between the two electrodes is maximum, and when the liquid to be measured is insulating, the capacitance between the two electrodes is a value corresponding to the dielectric constant of the liquid to be measured, and the capacitance between the two electrodes is the maximum. When there is no liquid to be measured between the electrodes, the capacitance between the two electrodes decreases dramatically (the dielectric constant of air is 1).
).

What is important in the present invention is that even in the case of level detection of conductive liquid, the impedance between the two electrodes is at least 1/jωC.
In the case of level detection of conductive liquids,
There is little change in impedance when detecting the level of an insulating liquid, and the level of a conductive liquid, an insulating liquid, and a mixture thereof can be detected with the same device.

Furthermore, an important effect of the present invention is that the electrode rod corrodes or rusts when exposed to corrosive liquids such as strong acids (e.g. aqua regia), strong alkalis, and sewage, or in corrosive gas atmospheres, reducing the signal voltage to be detected. This is because it can prevent fluctuations.

In the third invention, each signal voltage is sequentially inputted to the multiplexer from a plurality of detection electrode parts protruding from the insulating base through different signal line parts, thereby detecting a large number of liquid levels in time sequence.

In this way, a large number of liquid levels can be detected with less circuit load, although the detection time increases. for example,
N levels can be detected with N+'1 electrodes.

[Example] (First example) An embodiment of the present invention is shown in FIGS. 1 and 2.

This device includes a pair of electrode rods 200.300 hanging in parallel from an insulating substrate 10 at a predetermined distance from each other, a dielectric film 40.40 covering the surface of the electrode rods 200.300, and an insulating substrate 10. Lid part 6 forming sealed chamber 50
0, and an impedance detection section 70 provided on the insulating substrate 10 and housed in a sealed chamber 60.

The electrode rods 200 and 300 are made of stainless steel rods, and the dielectric film 40 is made of a PTFE resin film with a thickness Q of 1 mm.

The insulating substrate 10 is made of an alumina porcelain plate that also serves as a wiring board, and a wiring pattern (not shown) is formed on the surface of the insulating substrate 10.

The electrode rod 200.300 passes through the hole of this insulating substrate 10, and the upper end of the electrode rod 200.300 is in the closed chamber 50.
It is internally soldered to the above wiring pattern.

Further, on the insulating substrate 1, an impedance detection section 70 is provided.
Various electronic elements that make up the system are mounted.

The lid 60 is made of stainless steel and is fixed to the periphery of the insulating substrate 10 with an adhesive, and a hole 61 for taking out the signal cable 30 is provided in the center of the lid 60 .

The lid part 60 has an electromagnetic shielding function, and furthermore, in this embodiment, the signal line wiring distance between the electrode rod 200, 300 and the impedance detection part 70 is short, so attenuation of the AC signal voltage and noise contamination are prevented. A high signal-to-noise ratio can be obtained.

Next, regarding the impedance detection section 7, FIGS.
This will be explained in detail with reference to the drawings.

This impedance detection section 7 uses dilute sulfuric acid (conductive liquid).
It is applied to high/low level detection circuits.

The impedance detection section 7 includes a rectangular wave oscillation circuit 6 that applies a rectangular wave voltage of a predetermined frequency and a predetermined amplitude to the electrode bar 200, a first comparison amplification section 1, a first input terminal transition section 5, and a first comparison amplifier section 1. a detection section 7 that detects the output voltage of the amplification section 1;
Compare the output voltage Vn of the low-pass filter 8 with a predetermined second reference voltage Vr2 with a low-pass filter 8 that cuts high-frequency components including the carrier frequency from the detected voltage output from the detection section 7 and delays the detected voltage VZ. A second comparison amplifier section 3 amplifies the reference voltage input terminal of the second comparison amplifier section 2 and a second comparison amplifier section 3 which generates a transition voltage VC that follows the voltage change of the detection voltage The second input terminal transition section 4 is added to the input end of the input terminal transition section 5.

In this embodiment, alternating current voltage is applied between a pair of electrode rods 200 and 300, and changes in alternating current impedance between the two electrodes are binarized. The feature is that this is added to the first embodiment.

Here, the circuit and internal operation of the rectangular wave oscillation circuit 6 will not be described because they are not essential parts of the present invention.

The detection section 2 is composed of - diodes.

The low-pass filter 8 includes a capacitor C that connects its input end to VCC, a resistor r9 that connects its input and output ends,
It consists of a resistor r10 that connects its output end to VCC.

The operation of this circuit will be explained below with reference to FIG.

At time t1, both electrode rods 200 and 300 are not immersed in dilute sulfuric acid, and the alternating current impedance Z between the electrode rods is
Assume that X is extremely large. In this state, the resistances r1, r
2. Current flows only through r4, r5, and r6, and the voltage at point P is approximately equal to vi.

Therefore, this state is exactly the same as the state at time 1 of the first embodiment.

That is, the signal voltage Vi=14.3V, the output voltage vm of the first comparison amplification section 1 becomes a high level (here, 20V), and the diode D2 is cut off.

At this time, the node Z inside the low-pass filter 8 has a resistance r9,
It is charged through rlo, and the output voltage Vn becomes high level.

Next, a description will be given of the moment when the electrode rods 200 and 300 are immersed in dilute sulfuric acid at time t2. At this time, if the capacitance of the dielectric film 40 is 2CX, the AC impedance ZX becomes Zx=1/j(1)cX since dilute sulfuric acid connects both dielectric films 4Q in series. .

In this state, the AC output voltage of the rectangular wave oscillation circuit 6 is divided into ZX and the first input terminal transition section 5, and the AC voltage component is applied to the input terminal of the first comparison amplification section 1. Then, in the negative half cycle of the AC voltage, the signal voltage Vi applied to the input terminal decreases, and for the same reason as in the first embodiment, the output voltage Vm of the first comparison amplification section 1 becomes low level. On the other hand, in the positive half cycle of the AC voltage, the signal voltage Vi applied to the input terminal increases, and for the same reason as in the first embodiment, the output voltage vm of the first comparison amplification section 1 becomes high level.

In the end, the output voltage of the first comparison amplification section 1 is
．． When 300 is immersed in dilute sulfuric acid, a large amplitude AC voltage is generated as shown in FIG.

Even in this case, when Vm becomes a low level, the diode D2 becomes conductive, discharging the capacitor C at high speed, and lowering ■i and Vri through the second input terminal transition section 4 and the first input terminal transition section 5. The same effect as in Example 1 is obtained.

At time t3, the output voltage vm of the first comparison amplification section 1 is detected by the detection circuit 2, and the capacitor C is discharged through the diode D1 when 7m is at a low level, and charged through the resistors r9 and rlo when 7m is at a high level. is,
Cut the carrier signal (5kHz2) and set the binary output voltage y
It becomes n.

Next, at time t4, both electrode rods 200 and 300
Describe the moment when the water level dropped further.

AC signal current 1 due to a sudden increase in AC impedance ZX
(=Vp/Rx) decreases, so the signal voltage Vi=
Vp-Ibxr3 increases. Further, due to the decrease in the signal current Ib, the current flowing through the resistor r4 increases, so that the reference voltage Vr1 at one input terminal of the first comparison amplification section 1 decreases.

As a result, Vi becomes larger than Vrl in a short time,
The output voltage vm of the first comparison amplification section 1 becomes high level.

When Vm becomes high level, the diode D2 is cut off, and this cutoff causes the input/output state of the first comparison amplification section 1 to return to the state at time t1, as in the first embodiment.

Also, due to the increase in VC, the second comparison amplification section 3 equal to VC
The reference voltage Vr2 immediately rises.

On the other hand, due to the cutoff of the diode D2, the capacitor C is charged at a predetermined time constant via the resistors r9 and rlo. As a result, the potential ■n gradually changes to a high level.

What is important here is that, prior to the rise of vn, ■r2=V
Since c rises first, the substantial potential difference between the two is increased in this transient state.

In this way, even if ym reverses for a short time due to fluctuations in the liquid level during this transient period (i.e., even if Vm reverses from low level to high level and then immediately reverses back to low level), ), the signal voltage Vn delayed and high-frequency cut off by the low-pass filter 2 becomes the increased V
This short-term output reversal can be ignored without exceeding r2.

Furthermore, in this embodiment, the low-pass filter 8 for handling the carrier frequency delays Vm and cuts off high frequencies, so the circuit configuration can be simplified.

Incidentally, in the above embodiment, for example, rl is 3°3 ohm, r2 is 1 ohm, r3 is 4.7 to 100 ohm, r4 is 33 to 1 ohm, r5 is 1 to 1M ohm, r6 is 6.8 ohms, rl is 6.8 ohms,
r8 is 1.5 ohms, r9 is 2.2 ohms, rlo
may be 10 ohms and C may be 6.8 μF.

[Second example] Another embodiment of the invention is shown in FIGS. 3 and 4.

This embodiment is an apparatus for time-sequentially detecting multiple liquid levels of the above-mentioned dilute 5M acid.

This device includes eight electrode rods 200 to 207 that project horizontally from an insulating substrate 11 provided vertically at a predetermined interval from each other, and a dielectric film that covers the surfaces of the electrode rods 200 to 207. (not shown), a lid part 61 provided on the upper end of the insulating substrate 10 and forming a sealed chamber (not shown) therein, and a lid part 61 provided on the insulating substrate 10 and accommodated in the sealed chamber 60. The impedance detection section 71 (see FIG. 5) is provided.

The electrode rods 200 to 207 are made of stainless steel rods, and the dielectric film 40 is made of a PTFE resin film with a thickness Q of 1 mm.

The insulating substrate 11 is made of an alumina porcelain plate that also serves as a wiring board, and wiring tabs (shown by dotted lines) as signal lines are buried inside the insulating substrate 10.

Moreover, various electronic elements constituting the impedance detection section 71 are mounted on the insulating substrate 1 inside the sealed chamber, and each electrode rod 200 to 207 and the impedance detection section 71 are mounted.
and are individually connected by the above signal lines.

Next, this impedance detection section 71 will be explained with reference to FIG.

The impedance detection section 71 includes a multiplexer 72, an impedance detection circuit 73, a demultiplexer 74,
It consists of a pulse generator 75.

The signal lines from each electrode rod 200 to 207 are sent to an impedance detection circuit 73 via a multiplexer 72, and the output signal of the impedance detection circuit 73 is sent to an LED (light emitting diode) via a demultiplexer 74.
It is distributed to LEDI to LED8.

The pulse generator 75 individually sends eight pulse signals Φ1 to Φ8, which do not overlap each other and are formed at regular intervals, to the control terminals lower 1 to T8 of the multiplexer 72 and the control terminals D1 to D8 of the demultiplexer 74. supply

The circuit configuration of the impedance detection circuit 73 is the same as the impedance detection section 70 of the first embodiment, and the explanation thereof will be omitted.

The operation of this device will be explained.

In response to the input of the pulse signal, the multiplexer 72 selects two adjacent electrode rods 201 to 207 time-sequentially for a predetermined period of time, and connects one of them to the signal line L1 and the other to the signal line L2. Connecting.

Therefore, the impedance detection circuit 73 sequentially detects the liquid level (AC impedance) between two adjacent electrode rods. Then, the impedance detection circuit 73 sends its output signal V○ to a demultiplexer 74, and the demultiplexer 74 is operated in synchronization with the multiplexer 72 to sequentially distribute the output signal Vo to LED1 to LED8.

In this way, seven levels of liquid levels can be detected with a simple device.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing one embodiment of the present invention, Fig. 2 is a plan view thereof, Fig. 3 is a side view showing another embodiment of the invention, and Fig. 4 is a front view of the device shown in Fig. 3. 5 is a block diagram of the impedance detection section of the second embodiment, FIG. 6 is an equivalent circuit diagram of the impedance detection section, and FIG. 7 is a signal waveform diagram thereof. 1... First comparison amplification section 2... Low pass filter 2 3... First comparison amplification section 4... Second input terminal transition section 5... First input terminal transition section 200, 300... - Electrode rod 40... Dielectric film 10... Insulating substrate (case) 60... Lid (case) 70... Impedance detection section

Claims (3)

[Claims] (1) At least a pair of elongated electrodes arranged at predetermined intervals at predetermined positions in a container containing a fluid to be measured; a sealed case to which the proximal ends of the electrodes are fixed; and the sealed case. A level detection circuit comprising: an impedance detection section that is housed and has a signal input end connected to the electrode and detects impedance between the two electrodes. (2) an elongated insulating base erected at a predetermined position in a container containing a fluid to be measured; a plurality of detection electrodes arranged longitudinally on the surface of the insulating base; a plurality of signal line sections that are buried and individually connected at one end to each of the detection electrode sections and whose other end extends to one end of the insulating base; and one of each signal voltage from one end of each of the signal line sections. A level detection circuit comprising: a multiplexer that sequentially selects a signal voltage; and a detection section that detects a liquid level based on a signal voltage selected by the multiplexer. (3) at least a pair of electrodes each disposed at a predetermined position in a container containing a fluid to be measured; a capacitance detection unit that detects a capacitance between the two electrodes; 1. A level detection circuit comprising: a dielectric film that is electrically insulatively coated;