JPH0142008Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an electromagnetic flowmeter converter for converting a flow rate detection signal output from an electromagnetic flowmeter transmitter into, for example, a current signal having a predetermined span. The aim is to be able to do it accurately.

When the gain of an electromagnetic flowmeter transmitter fluctuates, errors in flow measurement occur. Therefore, it is necessary to periodically check the gain of the converter to determine whether the input-to-output relationship maintains the specified relationship. This test is generally called a span test. FIG. 1 shows an example of a conventional electromagnetic flowmeter converter with a span verification function. In the figure, 1 indicates an electromagnetic flowmeter converter, and 2 indicates an electromagnetic flowmeter transmitter that inputs a flow rate detection signal to the converter 1. As is well known, in the electromagnetic flowmeter transmitter 2, a pair of electrodes 4a and 4b are attached to a pipe 3 constituting a flow path in a direction perpendicular to the flow of fluid, and a pair of electrodes 4a and 4b are attached in a direction perpendicular to a line connecting the electrodes 4a and 4b. Excitation coils 5a and 5b are attached to
These exciting coils 5a, 5b are connected to a commercial power source 6, for example.
By exciting the electrodes 4a and 4b, a signal proportional to the flow velocity of the fluid is obtained from the electrodes 4a and 4b.
This detection signal is input to the input terminal 7-7 of the converter 1. The converter 1 includes a preamplifier 8, a span setting circuit 9, a divider circuit 10, an output circuit 11, a zero point adjustment circuit 13, and a simulated signal source 1 for span verification.
4 or the like. That is, in the preamplifier 8, the detection signal given from the transmitter 2 to the input terminal 7-7 is received by receiving amplifiers 8a and 8b at high input impedance, and common mode noise etc. are removed by the deviation amplifier 8c. It outputs at low impedance, has common mode noise removal and impedance conversion function, and has a gain of approximately 1.
Often located nearby. Span setting circuit 9
The amplifier is configured so that the gain of the amplifier can be adjusted so that the relationship between the input signal and the output current is a predetermined relationship. The divider circuit 10 divides the flow rate detection signal by a signal proportional to the excitation current flowing through the excitation coils 5a and 5b, thereby removing fluctuations in the flow rate detection signal based on fluctuations in the power supply voltage of the commercial power supply 6. . The output of the divider circuit 10 is supplied to an output circuit 11, where it is converted into a current signal having a predetermined span, and the current signal is sent out from an output terminal 12. This current signal is generally 4~20m
The span setting circuit 9 is set so that when the flow rate detection signal is zero, the output current corresponds to 4 mA, and when the maximum flow rate (flow rate) determined by the transmitter 2 is reached, the output current is 20 mA. The gain is set.

Incidentally, even when the flow velocity of the fluid flowing through the transmitter 2 is zero, a pseudo output is generally generated at the electrodes 4a and 4b. This pseudo output causes the output of the oscillator 2 to float at zero point. Therefore, in order to cancel this zero point floating and make the output current 4 mA when the flow rate is zero, a zero point adjustment circuit 13 is provided, and from this zero point adjustment circuit 13, when the flow rate is zero, the transmitter 2 A compensation voltage having the same magnitude as the zero-point floating voltage generated by the zero-point floating voltage is generated, and this zero-point compensation voltage is supplied to the preamplifier 8 to cancel the zero-point floating voltage.

The simulated signal source 14 for span verification is resistors R ₁ and R ₂
This voltage dividing circuit divides a signal proportional to the excitation current to generate a span verification simulation signal, and the span verification simulation signal is applied to the span verification switching circuit 15, which converts the span A test simulation signal is supplied to the preamplifier 8 during the test.

The span verification switching circuit 15 includes a switch 15a inserted between the input terminal 7-7 and the preamplifier 8.
15b, and the input terminal 7-7 constitutes the preamplifier 8 during flow rate measurement.
It is connected to the input terminals a and 8b. On the other hand, during span verification, the input terminal of one receiving amplifier 8a is connected to the common potential point, and the input terminal of the other receiving amplifier 8b is connected to the common potential point.
A simulated signal for span verification outputted from the simulated signal source 4 for span verification is applied to the input terminal of. Therefore, the gain of the span setting circuit 9 is adjusted so that the current value outputted from the output terminal 12 in this state becomes a predetermined value, for example, 20 mA.

By the way, in the conventional span verification switching circuit 15, the connection of the transmitter 2 is canceled during verification, and the span verification simulation signal is sent to the preamplifier 8 instead of the output signal of the transmitter 2.
I try to give it to Therefore, during span verification, the zero point floating voltage when the flow rate is zero is no longer input from the transmitter 2, so the zero point compensation voltage of the zero adjustment circuit 13 must be reset to zero. Therefore, at the end of the verification, it is necessary to perform zero point adjustment again so that a zero point compensation voltage having the same magnitude as the pseudo signal is obtained. In order to perform this zero point adjustment, it is necessary to stop the flow of fluid flowing through the flowmeter transmitter 2 and bring the flow rate to zero. It is difficult to stop the flow in the channel during actual operation. In reality, a side passage is provided in the flow meter transmitter section, and when performing zero point adjustment, fluid is passed through the side passage and the flow rate flowing through the flow meter transmitter 2 is brought to zero. For this reason, there is a drawback that equipment costs are high. Furthermore, by inserting the switching circuit 15 between the input terminal 7-7 and the preamplifier 8,
Since this part has a very high impedance, the switch 15a, which constitutes the switching circuit 15,
15b has high insulation resistance, and a switch with stable insulation resistance must be used. Switches with such high insulation resistance are expensive and have the disadvantage of increasing costs. Another disadvantage is that fluctuations in insulation resistance result in measurement errors.

The purpose of this invention is to provide an electromagnetic flow rate converter that does not require resetting the zero point compensation voltage of the zero adjustment circuit to zero during span verification, and therefore does not require re-adjusting the zero point.

In this invention, a span setting circuit is provided after the zero point compensation voltage supply point, and a verification switching circuit is provided between the zero point compensation voltage supply point and the span setting circuit to input a simulated signal for span verification. It was established. With this configuration, even if the verification switching circuit is switched to the verification state and a simulated signal for span verification is supplied to the span setting circuit through this switching circuit, the zero point compensation voltage supply point is in the previous stage, so the zero point Since span verification can be performed independently of the compensation voltage, there is no need to reset the compensation voltage of the zero point adjustment circuit to zero, and therefore, after span verification, the span verification switching circuit can be returned to its original state. It can be put into the measurement state immediately. An embodiment of this invention will be described below in detail with reference to the drawings.

FIG. 2 shows an embodiment of this invention. In Figure 2, parts corresponding to those in Figure 1 are given the same reference numerals and redundant explanation will be omitted. A span verification switching circuit for inputting a span verification simulation signal to the span setting circuit in place of the flow rate measurement signal is provided between this and a span setting circuit provided at a subsequent stage. In other words, in this example, a compensation voltage is supplied from the zero point adjustment circuit 13 to one input terminal of the deviation amplifier 8c constituting the preamplifier 8, and the zero point floating signal in the flowmeter transmitter 2 is canceled at this supply point. This shows the case when Incidentally, the supply point of this zero point compensation voltage may be supplied to either the input side of the receiving amplifier 8a or 8b as shown in FIG. The output of the preamplifier 8 is supplied to the span setting circuit 9 through the span verification switching circuit 15. In this example, the span verification switching circuit 15 is configured with one switch 15a. In the flow rate measurement state, the switch 15a is connected so as to give the output of the preamplifier 8 to the span setting circuit 9. At the time of verification, the switch 15a is connected so as to supply the span setting circuit 9 with a simulated signal output from the span verification simulated signal source 14 instead of the flow rate measurement signal.

In this way, by providing the span verification switching circuit 15 at the stage subsequent to the supply point of the zero point compensation voltage, the span verification can be performed regardless of the zero point compensation voltage. In other words, preamplifier 8
Since the gain is set to a sufficiently low value and is fixed at that low gain, the gain will not fluctuate over time. Therefore, accurate span verification can be performed without including the preamplifier 8 in the span verification. Therefore, a zero point compensation voltage is applied in the preamplifier 8 to cancel out the zero point floating of the oscillator 2, and since switching for span verification is performed at the subsequent stage, the zero point compensation voltage must be changed during span verification. You can perform a span test without it.
Therefore, the compensation voltage corresponding to the zero point floating voltage generated by the flowmeter transmitter 2 can be stored in the zero point adjustment circuit 13, so that the switch 15a of the switching circuit 15 can be returned to its original state after span verification. It is possible to immediately return to the original flow rate measurement state, so there is no need to stop the fluid flow and perform zero point adjustment again as in the conventional method, and there is an advantage that restarting after span verification can be easily performed. Furthermore, since the switching circuit 15 is inserted on the output side of the preamplifier 8, the impedance is sufficiently low in this part, so the switch 15 is
There is no need to use an expensive material whose insulation resistance is particularly high for a, and a reduction in cost can therefore be expected.

FIG. 3 shows another embodiment of this invention. In this example, the output of the preamplifier 8 and the span setting circuit 9 are connected via two series resistors R ₃ and R ₄ ,
The midpoint of the connection between these series resistors _R3 and _R4 is connected to a common potential point during span verification by a switch 15a constituting the span switching circuit 15, and at this time, a simulated signal for span verification is connected to the span verification signal through the switch 15b. A case is shown in which the signal is configured to be supplied to the setting circuit 9. By configuring the span switching circuit 15 in this manner, it is possible to avoid inserting a switch in series in the transmission path of the flow measurement signal. Therefore, even if the contact resistance of the switch changes over time, the span does not change, allowing stable operation and improving reliability.

FIG. 4 shows yet another embodiment of this invention. In this example, a simulated signal input terminal 16 for span verification is provided, and through this input terminal 16, for example, a span checker (not particularly shown) is input from the outside during span verification.
This shows a case where the configuration is configured to give a more simulated signal. In the end, in this design, the simulated signal source 1 for span verification
It is easy to understand that 4 is not required to be built into the converter 1.

Further, it is also possible to incorporate the span test simulation signal source 14 into the converter 1 and provide an external input terminal 16 so that the span test simulation signal can be supplied from the outside as required.

[Brief explanation of drawings]

Figure 1 is a connection diagram for explaining a conventional electromagnetic flowmeter converter with a span verification function, Figure 2 is a connection diagram showing an embodiment of this invention, and Figures 3 and 4 are of this invention. FIG. 7 is a connection diagram showing another embodiment. 1: Electromagnetic flowmeter converter, 2: Electromagnetic flowmeter transmitter, 8: Preamplifier, 9: Span setting circuit, 1
3: Zero point adjustment circuit, 15: Span verification switching circuit.

Claims (1)

[Scope of utility model registration request] A preamplifier that amplifies the voltage from the electromagnetic flowmeter oscillator by a certain factor, a simulated signal source that generates a simulated signal for verifying the span, and a zero point adjustment that generates a zero point compensation voltage to compensate for the zero point. a span setting circuit for setting a span, and a span verification switching circuit for switching between the output of the preamplifier and a simulated signal from the simulated signal source and applying the same to the span setting circuit, A compensation voltage is applied to the preamplifier to erase the zero point floating voltage from the electromagnetic flowmeter oscillator, and at the time of span verification, the span verification switching circuit is switched to the simulated signal source side to perform span verification. Electromagnetic flow meter converter.