JPH0450497Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an electromagnetic flowmeter, and more particularly to an electromagnetic flowmeter capable of detecting a non-full state of fluid in a conduit of an electromagnetic flowmeter transmitter.

Generally, in an electromagnetic flowmeter, as shown in FIG. According to the flow rate of the conductive fluid F flowing through the electrodes G ₁ and G ₂ , an AC voltage e ₁ is induced in one G ₁ of the pair of electrodes G 1 and G _{2, and an AC voltage e 2 having the opposite phase to e 1 is} induced in the other electrode G ₂ . . These voltages e ₁ ,
After DC components such as offsets are removed by capacitors C ₁ and C ₂ , e ₂ is led to a signal processing circuit (not shown) via high input impedance buffer amplifiers 3 and 4 and a differential amplifier. There is. By the way, in an electromagnetic flowmeter, when the degree of fluid filling in the pipe line falls below a permissible value and the pipe is not filled with water, the measured value of the electromagnetic flowmeter becomes unstable and does not indicate the actual flow rate. Therefore, it has been desired to detect the non-full state of the fluid in the pipe. Conventionally, as shown in FIG. 2, an AC power source 6 for detecting a non-full water state is connected to one electrode _G1 through a high resistance R, and the power supply voltage e _b of the AC power source 6 is connected to the high resistance R and the electrode in-beam. An alternating current voltage divided by the dancer is generated at the electrode _G1 , and this voltage is applied to the differential amplifier 5 via the buffer amplifier 3, and the output of the differential amplifier 5 is applied to the comparator 8 via the rectifying and smoothing circuit 7. In addition, a system has been proposed that detects a non-full water state based on a change in the output of the differential amplifier 5. In other words, when the pipe is full of fluid, the electrode is in contact with the conductive fluid, the electrode impedance is small, and the AC power supply 6 is in contact with the conductive fluid.
The voltage generated on electrode G ₁ by the power supply voltage e _b is small, but when the water is not filled, the electrode is not in contact with the non-electric fluid and the electrode _impedance becomes extremely _large . occurs in In this way, the voltage generated at the electrode G ₁ by the AC power supply 6 changes significantly between the full water state and the non-full water state, and since e _b ≫ e ₁ , the output e of the differential amplifier 5 changes in the non-full water state. ₅ also changes significantly. Therefore, the comparator 8, which monitors the voltage obtained by rectifying and smoothing the differential amplifier output _e5 , inverts its output when _e5 exceeds a predetermined value, and generates a non-full water detection signal AL. By the way, in such a configuration, since an AC voltage obtained by dividing e _b by the high resistance R and the electrode impedance is applied to the electrode _G1 , the resistance value of the high resistance R is sufficiently large and the If the electrode impedance at the time is sufficiently small, the influence of e _b on the flow rate measurement when the water is full will be sufficiently small, but in reality there is a limit to the resistance value of the high resistance R, and the electrode impedance is It changes significantly depending on the conductivity of the fluid, the combination of electrode material and fluid, dirt on the electrode, changes over time, etc.
For this reason, the circuit shown in FIG. 2 could not avoid the influence of e _b and had a practical problem. In particular, when the conductivity of the fluid is low, the influence of e _b is large and it cannot be applied.

In this invention, when DC current is applied to the electrode from a constant current source, the absolute value of the DC potential of the electrode changes from 0V to 2V even if the electrode impedance changes when the water is full, based on the electrochemical interaction between the electrode and the fluid. Using an operational amplifier as a pair of buffer amplifiers, we developed a means to flow the bias current to a pair of electrodes of an electrode flowmeter transmitter, and to monitor changes in the potential of either electrode. A practical non-full water detection circuit is provided which eliminates the above-mentioned drawbacks and does not impair the accuracy of fluid flow rate measurement by generating a non-full water detection signal when the potential of the electrode exceeds a predetermined value. This is a realization of an electromagnetic flowmeter.

FIG. 3 is a connection diagram showing one embodiment of the electromagnetic flowmeter of the present invention. The difference from the conventional example in Fig. 3 is that operational amplifiers are used as buffer amplifiers 3 and 4.
Using OP ₁ and OP ₂ , the bias currents I _B1 and I _B2 are made to flow to the electrodes G ₁ and G ₂ , and changes in the output of the buffer amplifier 4 are monitored by the comparator 9, and if the value exceeds a predetermined value, Non-full water detection signal
The point is that AL is generated.

In the present invention having such a configuration, when the water is full, there is a relationship as shown in FIG. 4 between the DC current I flowing through the electrode and the DC potential V of the electrode based on the electrochemical action between the electrode and the fluid. Furthermore, the absolute value of the DC potential V of the electrode is between 0 and 2V, and becomes constant regardless of the electrode impedance when the value of the DC current I reaches about 1nA to 1μA. and operational amplifier
Since the bias currents I _B1 and I _B2 of OP ₁ and OP ₂ are on the order of nA, the DC potential of electrodes G ₁ and G ₂ decreases when the water is full.
Vs ₁ and Vs ₂ are constant (approximately 2V). Therefore, the DC components of the outputs e ₃ and e 4 of the buffer amplifiers 3 and ₄ are also constant, and the DC components are removed by the differential amplifier 5. AC induced voltage e ₁ generated in electrodes G ₁ and G ₂ ,
Only the voltage e ₅ associated with the sum of e ₂ is obtained.

On the other hand, if the fluid in the pipe becomes not full, the electrode
Since G1 and G2 are open, electrodes G ₁ and G ₂
The DC potentials Vs ₁ and Vs ₂ of OP ₁ and OP ₂ rise to the power supply voltage Vb (for example, 15 V) of the operational amplifiers OP ₁ and OP _2.
output also increases. Therefore the threshold voltage of comparator 9 monitoring output e ₃ of OP ₁
For example, if Vth is set to 3V, when the water is not full,
Output of comparator 9 is inverted and non-full water detection signal
Generate AL. Furthermore, the amplitude of the induced voltages e ₁ and e ₂ generated in the electrodes G ₁ and G ₂ according to the flow rate of the fluid F is about 10 mV even when the flow rate is maximum, and does not affect the non-full water detection.

In this way, in this invention, flow rate measurement is performed using an AC signal, and non-full water detection is performed using a DC signal. Therefore, non-full water detection can be performed without impairing the accuracy of flow rate measurement. Therefore, the present invention can be effectively used even when the conductivity of the fluid is low.

In the above description, the case where positive bias currents I _B1 and I _B2 (in the direction of the arrow in the figure) are applied to the electrodes G ₁ and G ₂ is exemplified, but as is clear from the VI curve in FIG. The same thing can be done by flowing a bias current in the opposite direction of the arrow. In this case, when the water is not filled, the potential of the electrodes G ₁ and G ₂ becomes the negative power supply voltage of OP ₁ and OP ₂ -Vb (for example, -15V), so the threshold voltage Vth of the comparator 9 is set to, for example, -
Just choose 3V. Also, in the above, comparator 9
I gave an example of monitoring the output of OP ₂ , but OP ₁
The output of the electrodes G ₁ , G 1 ,
The potential of G ₂ may be monitored.

As explained above, in the present invention, the flow rate is measured using an AC signal, and the non-full water detection is performed using a DC signal, so the accuracy of flow rate measurement is not impaired and even when the conductivity of the fluid is low. An electromagnetic flowmeter having a practical non-full water detection circuit that can be effectively applied is obtained.

[Brief explanation of the drawing]

Figures 1 and 2 are connection diagrams showing an example of a conventional electromagnetic flowmeter, Figure 3 is a connection diagram showing an embodiment of the electromagnetic flowmeter of the present invention, and Figure 4 is a characteristic curve for explaining its operation. It is. 1... Electromagnetic flowmeter transmitter, L... Excitation coil,
G ₁ , G ₂ ... electrode, P ... pipe, 2 ... excitation circuit,
3, 4... Buffer amplifier, 5... Differential amplifier,
6... AC power supply for non-full water detection, 7... Rectifying and smoothing circuit, 8, 9... Comparator, C ₁ , C ₂ ... Capacitor, R... High resistance, OP ₁ , OP ₂ ... Operational amplifier.

Claims (1)

[Scope of utility model registration request] In an electromagnetic flowmeter having a high input impedance buffer amplifier in which induced voltages generated in a pair of electrodes of an electromagnetic flowmeter oscillator are individually applied, an operational amplifier is used as each of the pair of buffer amplifiers, and the bias current of the operational amplifier is A non-full water detection circuit comprising a means for supplying water to the pair of electrodes, and a means for monitoring output changes of either one of the pair of buffer amplifiers and outputting a non-full water detection signal when the value exceeds a predetermined value. An electromagnetic flowmeter characterized by the following: