JPS5837518A - Electromagnetic flow meter - Google Patents

Abstract

PURPOSE:To reduce the error of measurement on the basis of the ratio of the integrated value of a flow rate to that of an exciting current signal by controlling the conduction and cut-off of integrating switches for supplying the flow rate and the exciting current signals respectively to an integrator by a measurement controlling part and finding the integrated values of the flow rate and the exciting current signal outputted in each prescribed period. CONSTITUTION:A synchronous signal generated 26 by an AC signal ACIN from an exciter 2 is supplied to an interruption terminal INT of a measurement controlling part 27 and the porality direction of exciting current is controlled by the controlling part 27 to detect the flow rate at the inside of a conduit 43 and outputs a flow rate signal (e) from an amplifier 28. A flow rate signal discriminating signal POLI is supplied from a comparator 41 to the controlling part 27 and an exciting current signal (i) having the reversed phase against the signal (e) is outputted from the amplifier 29 in accordance with the signal POLI. Consequently, the controlling part 27 controls the conduction and cut-off of integrating switches 34, 35 for supplying said outputs to an integrator respectively to find the ratio Ni/Ne of an integrated value in the period of the high level of a flow rate signal measuring command EMF to that in the period of the low level of the command EMF and the high level of an exciting current signal massuring command CURR and to reduce the error of flow rate measurement on the basis of the found ratio.

Description

[Detailed Description of the Invention] The present invention relates to an electromagnetic flowmeter that measures flow rate using a measurement control unit such as a one-chip microcomputer, and its purpose is to suppress flow rate measurement errors to an extremely small level. An object of the present invention is to provide a new electromagnetic flowmeter.

FIG. 1 is an overall block circuit diagram of one embodiment of the present invention. The electromagnetic flowmeter of this embodiment is roughly divided into block circuits consisting of a transmitter 1, an exciter 2, and a detector 3. The transmitter 1 and the detector 8 are connected to each other via a flow rate signal line 4, and the transmitter 1 and the exciter 2 are connected to each other via an excitation current signal line 5 and an excitation current signal polarity direction switching control line 6.
, an exciting current polarity direction selection control line 7, and a synchronization signal line 8
Connected to Soiko via.

The transmitter 1 includes a synchronization signal generator 26, a measurement control section 27 such as a one-chip microcomputer, a current bt signal amplifier 28, an excitation current signal amplifier 29, an integrator 31, and a comparator 8.
2.41. It mainly consists of an integral switch 84.85, an erroneous voltage holding switch 86.37, and a photocoupler 88.42. The exciter 2 mainly includes an excitation power supply transformer 14, an excitation current detection transformer 15, a rectifier 16, 17, excitation current signal changeover switches 18-21, and excitation current signal changeover switches 22-25. The detector 3 includes field generating windings 9, 10 . Detection electrodes 11.12 and conduits 43
It mainly consists of.

The flow rate measurement operation using the flow meter in this example is performed in the second
This will be explained with reference to the drawings.

This occurs in the synchronization winding of the excitation power supply transformer 14 of the exciter 2. An alternating current signal ACIN as shown in FIG. 2(1) is input to the synchronization signal generator 26 via the synchronization signal line 8. This alternating current signal ACIN is a signal whose half cycle changes in the positive and negative directions at every timing t (i is a positive integer). A synchronization signal generator 26 including a photocoupler etc.
Each time such an alternating current signal ACIN reaches a maximum value or a zero value as in the present embodiment, a synchronization signal with a short pulse width of a high level (E) is generated as shown in FIG. 2 (2). Signal 5YNCi is generated. The synchronization signal SYNC output from the synchronization signal generator 26 is input to the interrupt port (INT) of the measurement control section 27. Measurement control section 27
When the synchronization signal 5YNC is input, the flow rate measurement processing program starts executing.

That is, at timing t2, when the synchronization signal SYNC is input to the measurement control section 270 (interrupt port) INT, a positive signal having a waveform as shown in FIG. Directional excitation command signal 1 ONF is sent. This command signal 1ONF is applied to the excitation current polarity direction changeover switches 18 and 19 via the positive direction control line 71 of the excitation current selection control line 7, thereby rendering these switches 18 and 19 conductive. .

Due to this conduction, a positive excitation current flows through the field generation windings 9 and 10 via the rectifier 16. Then, the field generating windings 9 and 1 disposed opposite to each other on the outside of the conduit 43
0 is excited in the positive direction, and this excitation causes a pair of detection electrodes 11.1 located inside the conduit 43 and facing each other in a direction orthogonal to the straight line connecting the field generation windings 9 and 1O to each other.
2, a signal is generated depending on the flow rate of the fluid flowing inside the conduit 48.

This signal is input to the preamplifier 28 of the transmitter 1 via the flow signal line 4, and after being amplified by this amplifier 28, it is output from this amplifier 28 as a flow rate signal e as shown in FIG. Output. The flow rate signal e is input into the comparison input terminal of a comparator 41 having a reference input terminal and a comparison input terminal, as indicated by reference symbols X and X in the transmitter l, and then is It is determined whether the voltage is positive or negative based on the voltage level. The flow rate signal e determined to be at a positive voltage level by this comparator 41
is inputted to the measurement control section 27 via the photocoupler 42 as a signal POL I for determining whether the flow rate signal is positive or negative as shown in FIG. 204.

The measurement control unit 27 sends out a negative-direction excitation current signal switching control signal C0NR from the terminal 5 in accordance with the content of the input flow rate signal positive/negative determination signal POL I. This control signal C0NR is manually applied to the excitation current signal changeover switches 24, 25 via one negative direction control line 61 of the excitation current signal polarity direction changeover control line 6, and thereby these switches 24. 25 is made conductive.

Due to this conduction, the excitation current signal line 5 receives the flow rate signal e.
An excitation current signal having a negative level and having an opposite phase flows therethrough [see FIG. 2 01].

In this way, the measurement control unit 27 counts the necessary number of synchronization signals 5yNC until the excitation currents flowing through the field generation windings 9 and 10 are saturated. This counting is performed until the excitation current is saturated at timing t6, which corresponds to the timing when the level of the excitation current signal 11 flow rate signal e stabilizes at a predetermined value. When such a counting operation is completed, a flow rate signal measurement command signal EMF and an exciting current signal measurement command signal CUR are output from terminals 2 and 8 of the measurement control unit 27, respectively.
R is sent [see Figure 2 (7) and (8)].

The signals EMF and CURR are applied to the integration switches 34 and 85, respectively, and these integration switches 84 and 85 are rendered conductive by the application of EMF and CURR. In addition, these signals EMF and CURR are shown in Fig. 2 (7L (8
), when the measurement stop command signal CNT reaches a high level (E), the measurement stop command signal CNT is sent from the terminal l of the measurement control unit 27 in coincidence with this timing t6.
becomes low level. The function of this measurement stop command signal CNT will be described later. In this way, the integral switches 34 and 35 are turned on, while the it pressure holding switch 36.
37 is blocked. Then, ii■ device width gauge 30,
Integral resistor 38, integral capacitor 39, and integrator 31
The integral conversion unit includes integral switches 84, , 85.
The meteor signal measurement command signal EMF and the excitation current signal measurement command signal CURR are sent through the integrator 3I of the integral conversion section. See figure■
.

The integral output eC changes from timing t6 to t due to charging operation.
Up to this point, the flow rate gradually rises in line with an integral curve, but during this rising period, the measurement control section 27 performs a counting operation for the necessary number of times in order to measure the flow rate. At timing t11 after the end of this counting, terminal 2 of the measurement control section 27
The flow rate signal measurement command signal EMF that was being sent from the controller is no longer at a low level, and one of the integral switches 34 is shut off [see FIG. 2 (see 7)].

At this time, the signal input to the integral conversion section is αQ in FIG.
Only the excitation current signal l shown in FIG. Since this signal 1 has a level in the negative direction, the integral output e of the integrator 31
. As shown in 2131'lO■, due to the discharge operation, after the timing t□1, the voltage gradually decreases. Then, in the middle of timing t12, when the level of the integral output becomes zero, the comparator 8 connected to the integrator 31
2. The comparative output CMP of the photocoupler 33 is shown in Fig. 2 01
As shown, the level is high. This comparator output CM
Although P was inputted to the measurement control unit 27 together with the detection signal POL I at a low level from timing t6 to the middle of t12, by being inverted to a high level, the excitation current measurement command signal CURR is The measurement control unit 27 is controlled to invert the signal to a low level. When the command signal cURR becomes low level, the other integral switch 35 is cut off. Also, at timing Lr3, when the synchronizing pulse signal 5YNC is input, the excitation command signal l0NF and the excitation command signal switching control # signal C0NR
is inverted to low level, and measurement stop command signal CNT is inverted to high level. As a result, excitation flux flow & direction changeover switch 18°19, excitation current G4
The - number changeover switches 24 and 25 are both cut off, while the false voltage holding switches 86 and 87 are both turned on.

The total 11111 control unit 27 controls timings t6 to tl when such a meteor signal measurement command signal EMF is at a high level.
o and the timing t11 when the flow hH74° measurement command signal EMF is at a low level and the excitation zero flow IH measurement command signal CURR is at a high level, from timing t11 to the middle of [1□, respectively, are integrated at high speed, The integrated value is Ne + N
I, and their integrated value Ne+ r Ni+ f
Store in the corresponding memories Me and Mi.

In this way, the calibration coefficients stored in the measurement control unit 270 memory etc.
The flow maximum measurement value V given by the following equation (1) from N1 is
It is calculated by the measurement control section 27.

V=ni-(1+ ±N1t7Ne+) Song...
(1) Here, the negative sign of NI means that when integrating the integrated value Ni, the circulation signal and the excitation current signal become in phase, such as when the flow of fluid flowing in the four pipes becomes opposite. is the sign of

The forward or reverse direction of the flow rate is determined from the excitation command signal 1ONF and the flow IIt forward/reverse determination signal POL I, and a sign is assigned to the flow rate measurement value V based on this. This code is used to determine whether the flow rate signal is forward or reverse when the flow rate signal is output.

The measurement stop command signal CNT controls the conduction and cutoff of the erroneous voltage holding switch 86.87, and through the conduction and cutoff of (7) y and +86.87,
Preamplifier 80 within the integral converter section. Integrator 31, comparator 3
The offset and drift of 2 is held as an error voltage in the capacitor 4o to improve the accuracy of the above-mentioned integration operation in the integral conversion section.

In this way, meteor measurement during positive direction excitation is completed.

Next, at timing t14, as shown in FIG. 2 (2), when the synchronous pulse signal 5YNC is input to the interrupt baud (INT) of the measurement control unit 27, the reverse excitation command signal 1ONR is sent from the terminal 6. is sent.

This command signal 1 ONR is the other reverse direction i of control Mt.
The excitation current is applied to the switching switches 20 and 21 via the secant line 72, thereby rendering these switches 20 and 21 conductive. Then, due to this conduction, an excitation current I flows in the field generation windings 9 and 10 in a reverse direction, contrary to the above-described positive direction excitation.

Corresponding to this excitation current in the opposite direction, the flow rate No. 18 in the negative direction flows from the counter electrodes 11. On the contrary, at timing t15 in FIG. 2(6), the positive excitation current signal switching control signal CONF is sent from the terminal 4 of the measurement side part 27. by this,
The excitation current signal changeover switches 22 and 28 are turned on, and the excitation current signal line 5 is connected to the timing [1] of FIG.
5, a positive excitation current signal flows.

In this way, from timing t15 onwards, the excitation current signal measurement command signal C
The reversal between high level and low level of each signal such as URR, flow rate signal measurement command signal EMF 1 measurement stop correction command signal CNT is detected and controlled, and as a result, the measurement control unit 27
The integrated values Ne- and Ni- are calculated for each corresponding memory.

In this way, the measurement cycle during reverse direction excitation is completed. Incidentally, a measurement error with respect to the flow rate value V measured as described above occurs when the excitation current signal fluctuates when calculating the integrated values Ne and N1. The flow rate measurement error ratio Δ&/V in such a case is expressed by the equation (1) in Thl.
Based on this, it is given by the following equation (2).

△V/V-C(+Ni/Ne)/(1±Ni/N
e ) ) ・(△i/i ) − (2) Here, O<N
The i/Ne ratio is 1, and Δi/i is the average fluctuation ratio of the excitation current signal i when calculating the integrated values Ne and Ni. From the values of the denominator and numerator in Ni/Ne, the result is the excitation current divided by the electromotive force. Therefore, even if the excitation current fluctuates and the electromotive force also fluctuates, the flow rate measurement error due to the division The impact on

In the prior art, a constant current circuit was used where the excitation current I was passed, but it was extremely difficult to pass a constant current of tens of A1 and hundreds of amperes.

In the present invention, instead of constant current, Ni/N
Fluctuations are suppressed by measuring the e ratio. However, since the current is measured after measuring the electromotive force, the fluctuation must be constant until the end of a specific period, but physically there is no sudden change, so even if there is a fluctuation, it is not practical. The above can be ignored. However, in order to suppress the fluctuation as much as possible, it is recommended to shorten the discharge time in the integrator 31 for the integral value Ni.
In the present invention, the integrated output level is prevented from becoming extremely large, and therefore the fluctuation can be suppressed to a small level.

In this way, the flow rate signal e and the excitation current signal l can be appropriately selected so that O<Ni/Ne<<1, so that the flow rate measurement error △■/Vft can be made sufficiently small. I can do it.

As explained above, according to the present invention, the flow rate measurement error △V/V in flow rate calculation processing, pilot measurement control, etc. is based on the integral value Ni/NeO ratio. It can be kept sufficiently small, so accurate flow rate measurement can be performed.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of one embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the embodiment shown in the first diagram. 1... Transmitter, 2... Exciter, 3... Detector, 4
...Flow rate signal line, 5...Exciting current signal line, 6...
Excitation current signal forward/reverse switching control line, 7... Forward/reverse excitation current selection control line, 8... Synchronization signal line, 9, 1o... Field generation winding, 11° 12... Opposing electrode, 13... Commercial power supply, 14... Excitation power supply transformer, 15...
Exciting current detection transformer, 16.17... Rectifier, 18
, 19, 20, 21 Excitation current changeover switch, 2
2, 2B, 24, 25... Excitation current signal forward/reverse switch, 26... Synchronization signal generator, 27...
Measurement control section, 28° 29.80... Preamplifier, 81
... Integrator, 32.41 ... Comparator, 83, 42
... Photocoupler, 84, 85... Integral switch, 86.87... Erroneous voltage holding switch, 38... Integrating resistor, 39... Integrating capacitor, 4o... Erroneous voltage holding capacitor, 43. ··conduit

Claims (1)

[Claims] means for generating a flow rate signal, means for generating an excitation current signal in response to the flow rate signal, signal integrating means;
a first integral switch interposed between the recording amount signal generating means and the signal integrating means; a second injection switch interposed between the excitation current signal generating means and the signal integrating means;
measurement control means for controlling conduction/interruption of the integration switch in response to the integral output from the signal integration means;
A second integrated value corresponding to the excitation current signal when the integral switch and the second integral switch are in the first conductive interrupting state is integrated via the measurement control means, and the first integrated value is An electromagnetic ammeter, characterized in that the flow rate is measured by the measuring means in relation to a fractional expression consisting of a value and a second integrated value.