JPH0128885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotation detection circuit that detects rotation of a rotating body.

As shown in FIG. 1, a conventional electronic water meter includes an impeller 1 that rotates at a rotation speed proportional to the amount of water used, and a permanent magnet 2 that controls the rotation of the impeller 1.
a shaft 3 that transmits signals to the magnet, a magnetoresistive element 4 that generates output signals having different phases from each other in response to the rotation of the permanent magnet 2, and a waveform shaping circuit 5 that amplifies and shapes the output signal of the magnetoresistive element 4. , a signal conversion circuit 6 that converts the output signal of this waveform shaping circuit 5 into a numerical value proportional to the amount of water used, and a display drive circuit 8 that drives a display section 7 that displays the content of the output signal of this signal conversion circuit 6. and these magnetoresistive elements 4,
It is comprised of a waveform shaping circuit 5, a signal conversion circuit 6, and a power supply 9 that supplies power to a display drive circuit 8.

In a water meter with such a configuration, since it is necessary to accurately detect the amount of water used, a magnetic resistance element 4 (hereinafter referred to as an MR element) is used as the waveform shaping circuit 5 as shown in FIG. A constant voltage is applied to the voltage, which changes as the direction of the magnetic field changes.
After taking out the voltage signal corresponding to the change in resistance value of the MR element 4 from the output terminal 10, the comparator 5a
input to one input terminal, and the reference voltage at the other input terminal.
A pulse signal is obtained by comparing with V _th . By the way, water meter impeller 1
rotates very slowly when the flow rate is small, so when the voltage at the output terminal 10 is near the reference voltage _Vth , a kind of chattering phenomenon occurs, that is, the output signal of the comparator 5a repeats on and off. There is a problem that may cause malfunction. Therefore, as a means to avoid the above phenomenon, the comparator 5a
It is conceivable to use a hysteresis comparator instead, but since this hysteresis comparator generally has a configuration in which the output voltage of the comparator is positively fed back by resistor division, for example, the output terminal 1
When the signal voltage input from 0 is small, if the hysteresis width becomes too large due to positive feedback, the sensitivity of the circuit decreases, and there is a drawback that rotation of the magnetic field cannot be detected accurately.

The present invention has been made in view of the above circumstances, and its purpose is to accurately detect the rotation speed of a rotating body using a digital circuit, and to detect the rotation speed of a rotating body very slowly. The present invention provides a highly reliable rotation detection circuit that does not malfunction even in the case of a rotation detection circuit.

Hereinafter, one embodiment of the present invention will be described with reference to FIG. In addition, in this figure, the same parts as in FIG. 1 are given the same reference numerals and will be explained. This electronic water meter includes an impeller 1 that rotates at a rotation speed proportional to the amount of water used, and a permanent magnet 2 that is attached to a shaft 3 of the impeller 1 and rotates in accordance with the rotation of the impeller 1. and a pulse detection circuit 11 that detects the rotation of the permanent magnet 2 as a change in the direction of the magnetic field, detects a change in the resistance of the MR element 4 as a change in the time constant of the monostable multivibrator, and converts the rotation of the impeller 1 into a pulse. A signal conversion circuit 6 that converts the rotation speed of the impeller 1, which is the output signal of the pulse detection circuit 11, into the amount of water used; and a display drive that drives the display unit 7 that displays the contents of the signal conversion circuit 6. circuit 8
and the pulse detection circuit 11, the signal conversion circuit 6,
It is composed of a display drive circuit 8 and a power supply 9 that supplies power to the display section 7.

Next, FIG. 4 is a diagram showing a specific example of a pulse detection circuit particularly having a hysteresis function in the electronic water meter of the present invention. In the same figure, 4 is the third
The MR element shown in the figure has three output ends 4a, 4b, and 4c. Ra, Rb are MR
Output ends 4 on both sides viewed from the center terminal 4c of the element 4
Shows resistance up to a and 4b. S is a switch that opens and closes in synchronization with the clock CLK1 applied to the flip-flop 21. In other words, this flip-flop 21 outputs a "1" signal, that is, a gate open signal, from the terminal Q every time the clock CLK1 is input, and also outputs a "0" signal, that is, the switching control signal, from the terminal to turn the switch S. is alternately switched to select output ends 4a and 4b, and is reset by inverter 22 after a time determined by time constant Rac due to selection of output end 4a and RbC due to selection of output end 4c. 23 receives an up designation signal U and a down designation signal D alternately in synchronization with the clock CLK1, and when the gate 24 is opened in response to a gate open signal from the flip-flop 21, an input signal is input through the gate 24. This is an up/down counter with a preset input that up-counts and down-counts the input clock CLK2 based on the specified mode, and outputs a different signal depending on which of the up count value and the down count value is larger. The input timing of the up/down designation signal U/D to the counter 23 is determined in advance based on the time constants RaC and RbC. Reference numeral 25 denotes a latch circuit that latches the output contents of the up/down counter 23 and outputs a different preset command signal depending on the output contents. This is done by Therefore, the latch contents of the latch circuit 25 are the resistors Ra,
This is a comparison of the magnitude of Rb. Although not shown, the clocks CLK1 to CLK3 are obtained from the same crystal oscillation circuit directly or by appropriate frequency division. Preset circuits 26-0 to 26-7 input preset values to the counter 23, and have the same function as a comparator having a hysteresis effect. Specifically, these circuits 26-0 to 26-7 are first circuits that input preset values through the output of the latch circuit 25 and the Q output, respectively.
AND gates 27-0 to 27-7 and second AND gates 28-0 to 28-7, and an OR gate 29 that inputs the outputs of these gates to the counter 23.
-0 to 29-7. 30 indicates the output end of the pulse detection circuit 11.

Next, in the electronic water meter configured as described above, the relative operation between the MR element 4 and the pulse detection circuit 11 shown in FIG. 4 will be explained. Now, when the clock CLK1 shown in FIG. 5a is input to the flip-flop 21, the flip-flop 21
A "1" signal as shown in FIG. At this time, Fig. 5c
When the up designation signal U is input to the counter 23 as shown in FIG. 2, the counter 23 performs up counting. On the other hand, due to the input of clock CLK1, the terminal of flip-flop 21 becomes "0",
Assume that the switch S is closed to the output end 4a of the MR element 4. Then, due to the "0" at the terminal, the threshold level is reached in a period based on the time constant RaC, and a "1" signal is output from the inverter 22 to clear the flip-flop 21 (see FIG. 5e).
Therefore, the up/down counter 23 has a time constant
Clock CLK2 is counted up for a period determined by RaC. Furthermore, continue to the next clock CLK1.
When input, the flip-flop 21 outputs a "1" signal from the terminal Q to open the gate 24.
On the other hand, in response to the "0" signal from the terminal of the flip-flop 21, the switch S selects the output terminal 4b, and the up/down counter 23 operates during the period of time constant Rbc obtained by selecting the output terminal 4b. Count down the clock CLK2 (see Figure 5b). Then, the count value of the up/down counter 23 is set to the latch circuit 25 by the clock CLK3 just before the input of the clock CLK1, as shown in FIG.
At the same time, the preset circuits 26-0 to 26-2 are latched based on the output Q of this latch circuit 25.
6-7 presets the counter 23 using a preset signal PRS (see FIG. 5g).

By the way, when the up-down counter 23 has an 8-bit (n=8) configuration, the preset circuit 26-
8-bit data is preset into the counter 23 in parallel by 0 to 26-7. The preset data is determined in advance by a switch, ROM, etc. (not shown) based on the hysteresis width. For example, the first AND gates 31-0 to 31
-7 input, 31-0="1" 31-1 to 31
−7="0" and the second AND gate 32-0
32-7 are set to 32-0 to 32-7="1", when the output Q of the latch circuit 25 is "1", the second AND gates 28-0 to 28-7 open and the terminals Data 32-0 to 32-7 are preset in the up/down counter 23. On the other hand, when the output Q of the latch circuit 25 is "0" (
=1), the first AND gate 27-0 opens,
Data on terminals 31-0 to 31-7 are preset in up/down counter 23.

Now, assuming that Ra > Rb and the number of clocks corresponding to RaC and RbC are Ta = 10 and Tb = 6, the up/down counter 23 initially counts up 10 and counts down 6, so the contents of the counter 23 are It becomes 4. In binary representation, { _MSB 0 0 0 0 0 1
0 _LSB 0 }, therefore, the MSB is 0, so
The output terminal Q of the latch circuit 25 becomes "0". On the other hand, since the output terminal of the latch circuit 25 is "1", when one up/down is completed, the counter 23 has +1, that is, {binary display 0 0 0 0
0 0 0 1} is preset, and if 10 up counts and 6 down counts, the contents of the counter 23 become 5. Therefore, as shown in Figure 6, Ra＞
If Rb remains unchanged, the contents of the counter 23 will be positive in the next U/D cycle, and the latch circuit 25 will be
The output terminal becomes "1" as shown in FIG. 6d.

Next, the values of Ra and Rb change, and Ra (Ta) = Rb
(Tb), the counter 23 is set to +1 because it has been Ra>Rb so far, so it is ="1". Then, the counter 23 counts up Ta and counts down Tb.
Since 1 remains in the counter 23, the latch circuit 25
The output of does not change. Furthermore, Ra>Rb→Ra=
Assuming that Rb→Ra<Rb changes and Ta=8 and Tb=10, the preset value is 1 and the counter 23
If it counts up by 8 and counts down by 10, the counted value is -1, that is, {Binary _MSB 1 1 1 1 1 1 1
1}, so the value of the latch circuit 25 changes to "0" at this time. Once ="0" (Q=
1), then -1, that is, {binary _MSB 1 1 1 1 1 1 1 1} is preset, so the output of the latch circuit 25 does not change even if it changes to Ra = Rb (Ta = Tb). .

Therefore, as shown in FIG. 6, the U/D period of the counter 23 (b in the same figure) is sufficiently fast compared to the change in magnetic resistance, and therefore, at A shown in FIG.
When Ra<Rb, the output of the latch circuit 25 becomes U/
It changes when one cycle of D ends. The above is
The counter 23 has an 8-bit configuration, and the preset data is fixed at +1 and -1. Generally, the counter 23 depends on the length of Ta or Tb. Furthermore, by changing the preset data, it is possible to change the hysteresis width. For example, 31-0=“1”, 31-3=
“1”, all others are “0”, +9, 3
It is also possible to change the positive and negative hysteresis widths by setting 2-2=“0” and setting all others to “1” to set it to -5. In addition, the present invention is not limited to the above embodiments, and can be implemented with various modifications. For example, in FIG. 4, the counter 23 and latch circuit 25 can be constructed using the memory of a microcomputer. At this time, the calculation procedure is performed according to the flowchart shown in FIG. In this case, clocks corresponding to the pulse width of the monostable multivibrator are sequentially counted up and down in the memory of the microcomputer. Then, it is determined whether the result is positive or negative, and preset data is set in the memory. Using the above procedure, the same effect as the circuit shown in FIG. 4 can be obtained. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

As described in detail above, according to the present invention, the pulse detection circuit subsequent to the MR element is processed digitally, so that the rotation of the rotating body can be accurately detected. Further, since the hysteresis width can be set using a digital signal for each bit width, the optimum hysteresis width can be set without lowering the sensitivity of the pulse detection circuit. Particularly, in applications where a microcomputer is used to detect the rotation of a magnet, a rotation detection circuit that can set arbitrary hysteresis can be provided by connecting a preset data line to a bus.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional electronic water meter, Fig. 2 is a block diagram of the waveform shaping circuit of Fig. 1, and Fig. 3 is a block diagram of a rotation detection circuit according to the present invention applied to an electronic water meter. , FIG. 4 is a specific configuration diagram of the pulse detection circuit shown in FIG. 3, FIGS. 5 and 6 are waveform diagrams explaining the operation of an electronic water meter according to an embodiment of the present invention, and FIG. It is a flowchart showing another example of the invention. DESCRIPTION OF SYMBOLS 1... Impeller, 2... Permanent magnet, 4... Magnetoresistive element, 6... Signal conversion circuit, 7... Display section, 8
... Display drive circuit, 11 ... Pulse detection circuit, 2
1...flip flop, S...switch, 2
3... Up/down counter, 24... Gate, 25... Latch circuit, 26-0 to 26-7...
...Preset circuit.

Claims (1)

[Claims] 1. A magnet that is attached to a rotating body that rotates in proportion to the physical quantity to be detected, and that changes with changes in the direction or strength of the magnetic field generated by the rotation of the magnet. In a rotation detection circuit that detects resistances Ra and Rb of resistive elements and measures the rotation speed of the rotating body, signal generating means generates a gate opening signal and a switching control signal every time a first clock signal is input; A capacitor c is connected between both resistors Ra and Rb of the front magnetoresistive element, and the resistor is alternately connected each time it receives a switching control signal generated from the signal generating means.
Ra and Rb are selected and operated, respectively.
c. a time constant circuit that sends a reset signal to the signal generating means to reset the gate open signal when a period determined by the time constant of Rb·c has elapsed; and a time constant circuit that receives the gate open signal from the signal generating means. a gate circuit that outputs a second clock signal during a period of time, and a second clock signal that is alternately set to up mode and down mode and output from the gate circuit in synchronization with the first clock signal. A counter with a preset input that counts up and counts down and outputs a different signal depending on which of the up count value or the down count value is larger, and the output contents of the counter before setting the up mode and the down mode. and a latch circuit that presets the counter to a predetermined positive preset value when the up count value is large, and to a predetermined negative preset value when the down count value is large, in accordance with the output content of the latch circuit. A rotation detection circuit characterized in that the rotation speed of the rotating body is measured from the output state of the circuit.