JPH03269231A - Measuring device having excessive-input detecting function - Google Patents

Abstract

PURPOSE:To make it possible to detect an excessive input even if a series signal exceeds a measuring period by comparing the magnitude of the width of a preceding pulse which is measured in a period with the magnitude of a specified reference pulse width when the series signals of the widths of two pulses exceed the measuring period, and judging the polarity of the excessive input. CONSTITUTION:When a negative pressure PL or a positive pressure PH is applied, capacitances C1 and C2 are increased or decreased through diaphragms D1 and D2. Pulses with pulse widths T1 and T2 which are proportional to the capacitances are outputted from an A/D converter 12. With respect to pulse width T1 which has exceeded a measuring period S1 in time, a microcomputer 13 measures the pulse width T2 and then measures the time up to the period S1. Then, the microcomputer performs sampling of only a time T11 up to S1 and judges whether the value is smaller or larger than a reference pulse width T2Z for T2 at the 0% input. Thus the positive or negative excessive pressure is judged and detected.

Description

[Detailed description of the invention] [Industrial application field]

The present invention is a measuring device using a microcomputer (for example, a capacitance pressure measuring device) mainly used in the field of industrial measurement, and is capable of detecting excessive input and determining its polarity without increasing the regular measurement time. This invention relates to a measuring instrument with an excessive input detection function. Note that in the following figures, the same reference numerals indicate the same or corresponding parts.

[Conventional technology]

For example, in a capacitive pressure measuring device, within a certain sampling period, the capacitance of the pressure sensing part on the (+) side and the capacitance of the pressure sensing part on the (-) side are proportional to two physical quantities. A method is used in which the differential pressure between the (''-) side pressure and the (-) side pressure is measured by time-divisionally detecting the pulse widths of the Either the instrument is capable of measuring only within the specified measurement range and does not guarantee measurement operation in the event of excessive input, or (2) it is, for example, ±1.5 times within the specified measurement range of the measuring device. Alternatively, the physical quantity to be measured up to an excessive input such as ±2 times is detected in a time-sharing manner, and the measurement period Sl (Fig. 1) described later is set long so that the detection time does not exceed the time limit. It is configured.

[Problem to be solved by the invention]

However, the above-mentioned measuring instruments have insufficient performance in (1), and in (2) the sampling period and therefore the time required for measurement are long, making them unsuitable as measuring instruments in the field of measurement and control. there were. Therefore, the present invention detects pulse widths proportional to two physical quantities (for example, capacitance) in a time-sharing manner within a limited short sampling period suitable for measurements in the field of measurement and control. An object of the present invention is to provide a measuring device with an excessive input detection function that can detect excessive input even if the time exceeds due to positive or negative excessive input.

[Means to solve the problem]

In order to solve the above problems, the measuring instrument of the present invention provides a first pulse width (such as T2, ) and a second pulse width (TI, etc.) are sequentially connected in series such that the first pulse width precedes the first pulse width with a slight time difference that can distinguish these two pulse widths. The first pulse width and the second pulse width are obtained by sampling within a predetermined measurement period (measurement period 31, etc.) from the rising point of the pulse width of 1, etc.), the first pulse width decreases and the second pulse width increases as the quantity to be measured increases in the positive (negative) direction, and the quantity to be measured increases in the negative (positive) direction. The first pulse width increases and the second pulse width decreases due to an increase in the direction, and the first pulse width and the second pulse width decrease due to an excessively positive or negative polarity input of the measured quantity. In a measuring instrument in which the serial signal consisting of
2Z, etc., hereinafter referred to as reference pulse width)).
At the end of the measurement period, a deviation of the serial signal is detected, and the first pulse width measured within the measurement period is compared with the reference pulse width, and the It is assumed that the apparatus is equipped with means (such as the microcomputer 13) for determining the polarity of excessive input of the measured quantity.

[For use]

When the serial signal of two pulse widths exceeds the sampling period (measurement period SL described later), it is determined from the magnitude relationship between the preceding pulse width measured within this period and the relevant pulse width when there is no human power. , determine excessive input and its polarity.

【Example】

The present invention will be described in detail below with reference to FIGS. 1 to 3. FIG. 2 is a block diagram showing the configuration of a capacitive pressure measuring device as an embodiment of the present invention. In the figure, 1 is a pressure measuring device, 2 is a DC power supply, and 3 is a 2 converting the output current of the pressure measuring device from 4 to 20 mA to 1 to 5 V.
With a voltage conversion resistor of 50Ω, this pressure measuring device converts the measured pressure value into a current value of 4 to 20 mA and outputs it. The pressure measuring device 1 includes a pressure detecting section 11, and this detecting section 11.
an A/D converter 12 that digitally converts the detection signal of
A microcomputer 13 calculates pressure from the output data of this A/D converter 12 and outputs current data corresponding to this pressure value, and a D/A converter 14 converts the output data of this microcomputer 13 from D/A to a current value. Consists of etc. In the pressure measuring device 1, the capacitances CI and C2 change as described later in response to the pressure received by the pressure detection unit 11, and these capacitances CLC2 are converted into respective capacitances by the A/D converter 12. Convert to a pulse width proportional to the value. The microcomputer 13 counts these pulse widths based on the clock, and calculates the capacitance CLC2 as a physical quantity.
Detects sampling data proportional to , calculates a detected pressure value based on this sampling data, and calculates data to be given to the D/A converter 14 in order to obtain a current output corresponding to this detected pressure value. and output it. Then, the D/A converter 14 performs D/A conversion corresponding to the calculation output data of the microcomputer 13, thereby producing an output of 4 to 20 mA. Here, the pressure detection unit 11 includes a diaphragm D1 to which a negative pressure PL is applied, a diaphragm D2 to which a positive pressure PH is applied, and electrodes 101 and 102 fixedly provided inside each of the diaphragms DI and D2. , an electrode 100, etc., which is provided in the center and can be displaced to the left or right depending on the pressure difference between the left and right chambers. Here, the capacitance between electrodes 101 and 100 is CI, and electrode 102 is
The capacitance between and 100 is 02. The operating principle of this pressure detection unit 11 is, for example, when a positive pressure PH
When is applied, the central electrode 100 moves to the left in the figure via the PH side diaphragm D2 in response to this pressure, and the capacitance C1 increases and C2 decreases. Conversely, when negative pressure PL is applied, 01 decreases and C2 increases. FIG. 3 shows the pressure applied to the pressure detection unit 11 and the capacitance C.
The relationship with LC2 is schematically shown. In the AD converter 12, the capacitances CI and C2 are charged from the DC power supply with the voltage Vcc through the resistors R1 and R2, respectively, and when the charging voltage reaches the threshold voltage vth, the capacitances C1 and C2 are charged, respectively. discharge,
This charging and discharging process is repeated N times in succession. And by these N times of oscillation, the capacitance CI,
It outputs a pulse width TLT2 proportional to the capacitance CLC2 as the time for charging and discharging C2 N times. FIG. 1 shows an example of the pulse width and TLT2 waveform outputted from the A/D converter 12 to the microcomputer 13 in this manner. Here, if we ignore the discharge time of capacitance CLC2,
The pulse width TI and T2 are expressed by the following formula (1). TLT2: Time constant (pulse width) corresponding to C1 and C2
, N: constant (number of times of charging and discharging), CL, C2: capacitance, RLR2: resistance value of the resistor connected in series to CI and C2, respectively, Vth: threshold voltage of A/D converter, Vcc: A /D converter circuit voltage. The microcomputer 13 sequentially switches the A/D converter 12 to measure CI or C2, and each measures the capacitance C.
By sequentially counting pulse widths TI and T2 proportional to LC2 with reference to its own clock, sampling data indicating the pulse widths Tl and T2 can be obtained. Next, using FIG. 1, the relationship between the pulse width TLT2 proportional to the capacitances CI and C2 and the period S1 in which the microcomputer 13 measures these TI and T2 will be explained. Here, within the measurement period Sl, the pulse width T2. The following description assumes that sampling is performed in the order of TI. In addition, ■~ in the same figure
The numbers (3) indicate various pressure states applied to the pressure detection section 11, and these states correspond to the states with the same numbers in FIG. Taking a differential pressure type pressure detector as an example, it is usually possible to measure a differential pressure of -100 to +100% of the specified measurement range, and ■ indicates PH = PL, that is, at 0% input pressure. The pulse width T2 of
．． Let it represent TI. ■When the input pressure is +100% (positive) of the specified measurement range, ■
Similarly, the pulse width T2. is the pulse width when a -100% (negative) input pressure is applied. Let it represent TI. For input pressure 0 of ±(100+α)(%) in the measurement range, sampling data T2. Both TI measurements are completed within the measurement period Sl, and (T2+TI)<31. The pressure measuring device uses the sampling data Tl and T2 to
The microcomputer 13 performs calculations and the D/A converter 14 performs D/A conversion corresponding to the results, thereby making it possible to produce a measurement output of 4 to 20m8. Digital circuit input adjustment (zero adjustment, span adjustment)
Apply input applied pressure of 0% and 100% to the measurement range, and then calculate T2. This is possible by storing the calculated value by TI or T2T1 in memory. It is assumed that the pulse width T2 at the time of 0% reference input shown in FIG. As shown in Figure 1, ±(1
For input pressure within 00+α)%, (T2+TI)≧
31! It is assumed that the period S1 is set so that this does not occur. Next, ■ shows a state in which positive overpressure is applied. Here, (T2 + TI)≧31, but for a pulse width TI that exceeds the period S1, the microcomputer 13 calculates the time Tll from measuring the pulse width T2 to the period S1.
It is assumed that the true TI shown by the dotted line is not measured. Therefore, the microcomputer 13 determines a positive overpressure based on the conditions that the measurement of the pulse width T2 is completed and the measurement of the pulse width T1 is not completed, and the condition that T2 at this time is 72<T2Z. be able to. Conversely, when a negative overpressure is applied as shown in ■, the microcomputer 13 completes measurement of the pulse width T2 within the period Sl;
The pulse width TI is determined by the condition that the measurement is not completed and T2 at this time.
Under the condition that T2 > T2Z, negative overpressure can be detected. Furthermore, as shown in ■, if an overpressure that is more negative than ■ is applied, the measurement is not completed because the true T2 exceeds the time relative to Sl as described above, and the time T2 up to the period S1 is changed to T2.
21, it becomes possible for the microcomputer 13 to detect negative 1 2 overpressure within the cycle Sl under the condition that "the measurement of the pulse width T2 is not completed and T21>T2Z" as in (2). In this way, 72. When sampling data corresponding to physical quantities in the order of TI, ± of the measurement range
Even if excessive human force exceeding (100+α)(%) is applied, rT2. Whether Tl is positive or negative by determining whether the measurement has been completed and whether T2 at the time of pressure application is larger or smaller than the reference pulse width T2Z which is obtained by memorizing the pulse width T2 at the time of O% input. It becomes possible to distinguish and detect excessive pressure input. For explanation purposes, T2. It was assumed that sampling data was measured in a time-sharing manner in the order of TI, but conversely, T
Even if sampling is performed in the order of I and T2, T1 at 0% input is memorized as the reference pulse width TIZ, and similarly, it is possible to check whether rTl and T2 have been measured or not, and whether T1 at the time of pressure application is relative to TIZ. By determining whether the pressure is large or small, positive or negative overpressure can be detected.

【Effect of the invention】

According to the present invention, the pulse 1 width T2 and the pulse width TI, which are proportional to the two capacitances CI and C2 that change depending on pressure, are separated by a slight time difference that can distinguish these two pulse widths, and the pulse width is The pulse width T2 and the pulse width TI are obtained by sampling the serially connected signals sequentially so that the pulse width T2 precedes the pulse width T2 within a predetermined measurement period S1 from the rising edge of the pulse width T2, and the pressure is measured. In the measuring device 1, the pulse width T2 decreases and the pulse width 1 increases as the pressure increases in the positive direction, and the pulse width T2 increases as the measured quantity increases in the negative direction. The pulse width T1 decreases, and the pulse width T2 decreases due to excessive input of the positive or negative polarity of the pressure.
The serial signal consisting of the pulse width T1 and the measurement period S
In a pressure measuring device that can deviate from 1,
a memory serving as a means for storing a reference pulse width T2Z as the pulse width T2 when the pressure is 0; detecting deviation of the series 3 4 signal at the end of the measurement period S; The microcomputer 13 is provided as means for comparing the magnitude of the pulse width T2 measured in Sl with the reference pulse width T2Z to determine the polarity of the excessive pressure input. Excessive input of the pressure saw and its polarity can be determined without increasing the measurement time, and the function of the pressure measuring device can be easily improved.

[Brief explanation of drawings]

FIG. 1 is a time chart showing the operation of essential parts as an embodiment of the present invention. FIG. 2 is a block diagram showing an example of the configuration of a pressure measuring instrument that performs the operation shown in FIG. FIG. 3 is a characteristic diagram showing an example of the relationship between capacitance and applied pressure.

Claims (1)

[Scope of Claims] 1) The first pulse width and the second pulse width, which are each proportional to two physical quantities that change depending on the quantity to be measured, are separated by a slight time difference that can distinguish these two pulse widths. 1st
Sequentially, serially connected signals are sampled within a predetermined measurement period from the rising point of the first pulse width so that the first pulse width and the second pulse width are obtained, A measuring instrument for measuring the quantity to be measured,
As the quantity to be measured increases in the positive (negative) direction, the first pulse width decreases and the second pulse width increases; similarly, as the quantity to be measured increases in the negative (positive) direction, the first pulse width decreases. As the pulse width increases, the second pulse width decreases, and due to an excessive input of positive or negative polarity of the measured quantity, the serial signal consisting of the first pulse width and the second pulse width decreases. In a measuring instrument that can deviate from a measurement period, the device includes: means for storing the first pulse width (hereinafter referred to as reference pulse width) when the quantity to be measured is 0; and an end of the measurement period. detecting a deviation of the series signal at a time point, and comparing the magnitude of the first pulse width measured within the measurement period with the reference pulse width to determine the polarity of the excessive input of the measured quantity; A measuring instrument with an excessive input detection function, characterized by comprising means for detecting excessive input.