JPH03242513A - Time sharing driving system for sensor - Google Patents

Abstract

PURPOSE:To obtain a flow pulse in a simple circuit structure by adjusting the voltage at a source terminal of a sensor part corresponding to the output level of a hysteresis circuit thereby to drive the sensor part by a sink current or a source current. CONSTITUTION:When the output voltage of a sensor part 1 is increased from the lower part of a higher threshold value to the threshold value, an output of a hysteresis circuit 9 becomes H level, so that the sensor part 1 is driven in a time sharing manner by a sink current. When the output voltage of the sensor part 1 is decreased to the lower threshold value, the output of the hysteresis circuit 9 becomes L level, and the sensor part 1 is time-sharing-driven by a source current.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a time-division driving method for sensors.

[Conventional technology]

In flowmeters such as water meters and gas meters, a magnet is attached to a rotating body that rotates once every time a certain amount of water or gas flows, and a magnetic sensor detects the rotation of this magnet and converts it into an electrical signal.
The amount of water and gas used is calculated by counting the number of electrical signals. In order to extend battery life, the sensor is driven in a time-division manner to reduce power consumption.

In FIG. 5, 1a is a magnetic sensor, which is a well-known magnetoresistive element that detects the rotating magnetic field of a magnet (not shown). R1
and R2 are voltage dividing resistors for generating a reference voltage, and 1b is an OP amplifier that constitutes a differential amplifier together with resistors R3 and R4.
These magnetic sensor 1a, voltage dividing resistors R1 and R2, OP amplifier 1b, and resistors R3 and R4 are connected as shown in the figure to constitute a sensor section 1. The sensor section 1 shown in FIG. 5 is configured to sink the sensor section by fixing one power supply terminal V to an H level and lowering the voltage of the other power supply terminal V to an L level for a short period of time t every period T. I was driving and using it (
Note that the term "sink drive" is not a common term, but is the name used in this specification.) The power terminal ■- is at H level outside the clothes during the short time t when it is being driven (see Figure 6B).
.

The output voltage of the output terminal ○ of the sensor unit 1 in FIG. 5, which is time-divisionally driven by the sink drive in this way, becomes an analog output that changes sinusoidally in accordance with the rotating magnetic field of the magnet (not shown). (See diagram 6).

And this output voltage is
That is, since both power supply terminals v+ and v- are at the H level during the short time t of one period T when the clothes are not worn, the output voltage of the output terminal ○ is also at the H level. And the sixth
The broken line A in the diagram indicates the sinusoidal envelope.

In addition to being time-divisionally driven by sink driving as explained in FIGS. 5 and 6 above, the sensor section 1 is also driven by time-divisionally by source driving as shown in FIGS. 7 and 8. (Note that the term "source drive" is not a common term, but a term used in this specification).

In this source drive, the other power supply terminal V is grounded to GND and fixed at L level as shown in FIG. Source drive the sensor unit 1 by raising the
(See Figure 8A).

The voltage of the power supply terminal (1) is at L level outside the clothes during the short time t during driving. Therefore, the output terminal of the sensor section ○
As shown in Figure 8, the output voltage becomes a sinusoidal analog output whose envelope is shown at the end of the broken line in response to the rotating magnetic field of the magnet. The output voltage of this output terminal 0 is such that while the sensor unit is not driven, that is, for a short time t within one period T, both power supply terminals V" and - are at the L level outside the clothes. Therefore, it is naturally at L level.

To calculate the integrated flow rate as a flowmeter, it is inconvenient to see the output voltage waveform of the output terminals shown in Figures 5 and 7, which are time-divisionally driven by sink drive or source drive, so it is necessary to use a so-called sample-and-hold method. It is necessary to shape the waveform and obtain a flow pulse that corresponds to the rotation of the magnet.

Figure 9G shows just such a circuit. In FIG. 9, reference numeral 1 is the sensor section, in which case the sampling pulse from the sampling pulse generation circuit 2 is applied to one power supply terminal (2) via the buffer 3, and the other power supply terminal is connected to GND and As explained in FIGS. 7 and 8, the sensor section 1 is fixed at the level and is time-divisionally driven by source drive.

4 is a sampling switch, 5 is a hold capacitor, and 6 is a high input resistance amplifier, which together with the capacitor 5 constitutes a hold circuit 7.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, the voltage at the output terminal ◯ of the sensor section 1 temporarily becomes H level in sink drive and becomes L level in source drive while no drive voltage is applied to the sensor section. Then, the output voltage waveform of output terminal 0 is the sixth
As shown in FIG. 8D4, the pulse waveform has a short pulse width t, so there is a problem that the circuit cannot have hysteresis and is susceptible to noise. Further, in order to shape the waveform to obtain a flow rate pulse, a hold circuit using a hold capacitor as shown in FIG. 9 is required, resulting in a complicated circuit.

In view of the above, it is an object of the present invention to provide a time-division system for a sensor that has a relatively simple circuit configuration and has hysteresis.

[Means to solve the problem]

In order to achieve the above object, the time division driving method of the present invention includes a sensor unit (1) whose output voltage is an analog output, and a sensor unit (1) whose output voltage is an input, and which has two threshold values vT. Hysteresis circuit with □8 and V THL (
9, 9'), and this hysteresis circuit (9, 9')
, 9') is at H level, the voltage at one power supply terminal ■" of the sensor section (1) is fixed at H level, and the voltage at the other power supply terminal V- is shortened every cycle T. L for each time t
When the output of the hysteresis circuit (99゛) reaches the L level, the voltage at the other terminal ta of the sensor section (1) is fixed at the L level. The voltage of the one power supply terminal V+ is set to a period T
The sensor section is configured to be source-driven by raising the voltage to the H level for a short time t each time.

[Function] Threshold value VTHH of the higher output voltage of the sensor section (1)
When the voltage rises from below and reaches the threshold value V THH, the output of the hysteresis circuit (9, 9') becomes H level, and the sensor section (1) is time-divisionally driven by sink driving.
When the output voltage of the sensor section (1) decreases and reaches the lower threshold value V THL, the hysteresis circuit (9, 9'
) becomes L level, and the sensor section (1) is time-divisionally driven by source drive.

[Embodiment] In the first embodiment shown in FIG. 1, numeral 1 is the same sensor section as the sensor section of the prior art, and 2 is the same sampling pulse generation circuit as the prior art, as shown in FIG. 2A. , a short pulse of time t is output every cycle T. 8 is OR gate, 9
is a Schmitt trigger circuit as a hysteresis circuit, with a higher threshold value V THH and a lower threshold value V
Equipped with THL and hysteresis V T) +8 V TH
It has L. 10 is an inverter, and 11 is an AND gate, which are connected as shown in the figure.

Next, the operation of the embodiment shown in FIG. 1 will be explained based on the timing chart shown in FIG.

The magnetic sensor 1a responds to the magnetic field of a rotating magnet (not shown).
When the resistance value changes, the voltage at the output terminal O of the sensor section 1 changes as shown in the second diagram, and reaches the higher threshold value V THH at the time shown in A of the diagram. Until now, the output of the Schmitt trigger circuit 9 has been at L level (second
(See Figure C), the AND gate 11 is closed, the source terminal V- is fixed at the L level (see Figure 2C), and the H level drive voltage with a short width t is applied to the power supply terminal V+ every cycle T. (see FIG. 2C), and the sensor section 1 is source-driven. The output of the Schmitt trigger circuit 9 is at L level (see FIG. 2C).

When the output of the Schmitt trigger circuit 9 reaches the high point,
It changes to level and switches to sync drive.

Next, at the point shown in the mouth, the threshold value VTHL is reached from above,
The output of the Schmitt trigger circuit 9 becomes L level, and the drive is switched to source drive again. Furthermore, at the time point shown in C, the threshold value V THH is reached from below, the output of the Schmi-node trigger circuit 9 becomes H level, and the drive is switched to sink drive again.

In this way, a rectangular wave-like flow pulse is obtained at the output of the Schmitt trigger circuit 9, and since the period of this flow pulse corresponds to the change in the rotating magnetic field detected by the magnetic sensor 1a, this flow pulse ( By counting D') in FIG. 2, the integrated flow rate can be obtained.

In the second embodiment shown in FIG. 3, 1 is a sensor section, 2 is a sampling pulse generation circuit, 8 is an OR gate, 10 is an inverter, 11 is an AND gate, and 9a'' is a D-FF. , R5, and R6 are hysteresis resistors, which are connected as shown. The latch circuit 9a' and the hysteresis resistors R5 and R6 constitute a hysteresis circuit 9'. The hysteresis of the hysteresis circuit 9' can be determined by selecting the ratio of the hysteresis resistors R5 and R6 to a normal value. As shown in the fourth diagram, this hysteresis circuit 9'' is equipped with two threshold values ■, □ and VTHL.
In the embodiment, the hysteresis circuit 9' includes a latch circuit 9a' consisting of a D-FF that latches the level of the terminal in synchronization with the sampling pulse, and hysteresis resistors R5 and R.
6 is slightly different from the first embodiment, but since the operation is almost the same, a detailed explanation will be omitted, but it can be easily understood from the timing chart of FIG. 4A-D'. It will be. Note that the output of the sampling pulse generation circuit 2 has the same waveform as that shown in FIG. 2A.

[Effects of the Invention] Since the time-division driving method of the present invention has the above-described configuration, a flow rate pulse can be obtained with a simple circuit configuration without requiring an analog hold circuit that holds with a capacitor, etc. It has the advantage of being resistant to noise because it has hysteresis.

[Brief explanation of drawings]

1 is an electric circuit diagram of a first embodiment of the present invention, FIG. 2 is a timing chart thereof, FIG. 3 is an electric circuit diagram of a second embodiment of the present invention, FIG. 4 is a timing chart thereof, and FIG. 6 is a diagram showing the main part of an electrical circuit of the prior art, FIG. 6 is a timing chart thereof, FIG. 7 is a diagram showing a main part of another electrical circuit of the prior art, FIG. 8 is a timing chart thereof, and
The figure is yet another electrical circuit diagram of the prior art.

Claims (1)

[Claims] It has a sensor part (1) whose output voltage is an analog output, and a hysteresis circuit (9, 9') which takes the output voltage of this sensor part (1) as an input and is provided with two threshold values V_T_H_H and V_T_H_L. Therefore, when the output of this hysteresis circuit (9, 9') is at H level, the voltage of one power supply terminal V^+ of the sensor section (1) is fixed at H level, and the voltage of the other power supply terminal V^+ is fixed at H level. - is lowered to L level for a short period of time t every period T to drive the sensor section in sink mode, and when the output of the hysteresis circuit (9, 9') reaches L level, the sensor section (1) Said other power supply terminal V^
- is fixed at L level, and the one power supply terminal V
A sensor time-division drive system in which the sensor section is source-driven by raising the voltage of ^+ to the H level for a short time t every period T.