JPH03102220A - Level measuring apparatus - Google Patents

Abstract

PURPOSE:To enhance the speed of measurement by providing a controlling means which controls to switch from one LPF to another, having a desired time constant, after a predetermined time determined by individual time constants of a plurality of different LPFs. CONSTITUTION:Supposing that measurement is done within a certain measuring range 1a, if an output goes beyond the current measuring range, the range is switched to the measurable range 1a by a switching signal S1 from a measuring range judging part 4. In consequence to this change of the measuring range, a second LPF 2b is selected via a filter switching part 6 by a switching signal S3 output from a filter controlling part 5. As a result, a signal is output in accordance with the time constant of the filter 2b and measured. Then, when the output is controlled to a final value after a time based on the time constant of the filter 2b passes, a first LPF 2a is selected by the signal S3 from the controlling part 5 thereby to generate and measure a signal in accordance with the time constant of the filter 2a. Signals output from the filters 2a, 2b are measured at 3 and sampled at 7, and the maximum value is stored at 8 and displayed at 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a level measuring device that converges the finally output signal level to a predetermined level range by switching the measurement range.

[Prior Art] For example, in a measuring instrument, in order to increase the speed of signal processing and obtain a wide dynamic range, several measurement ranges are provided so that the level of the final output signal converges within a predetermined level range. A method is used in which the measurement range is automatically switched one by one, thereby measuring signals within a certain range. In this case, the input signal is a sine wave or a square wave,
A low-pass filter is required to transversely convert the signal into a stabilized DC signal.

Figure 8 shows the schematic configuration of a level measuring device using such a low-pass filter. In this level measuring device, a feedback resistor r forming a plurality of measurement ranges 2l is connected in parallel to an amplifier 20, and a low-pass filter 22 consisting of a resistor R and a capacitor C is connected in series after the amplifier 20. When the measurement range 2l is switched according to
Multiply by 1 to change to the final value.

[Problem to be Solved by the Invention 1] However, in the conventional level measuring device described above, it takes time t1 for the output to converge to the final value after the measurement range 2l is switched, and this causes the measuring device to There was a problem with slowing down the speed. Therefore, in order to solve the above-mentioned problem, the time constant of the low-pass filter may be reduced, or, as shown in FIG. The aim was to increase the measurement speed by increasing the speed. However, this method has a problem in that the signal cannot be smoothed sufficiently and stability deteriorates.

On the other hand, when measuring the optical power level using an optical power meter, the above-mentioned level measuring device is used to eliminate the effects of photodetector drift, achieve high sensitivity, and enable measurement down to low levels. in this case. The signal is treated as alternating current, and after detecting this alternating current signal, it is smoothed through a low-pass filter and converted to a direct current signal, but this N!
In order to sufficiently smooth the wave signal, a low-pass filter with a certain degree of time constant is required.

By the way, when setting the time constant of a low-pass filter in order to sufficiently smooth the signal, if the frequency #t of the signal to be handled is high, it is possible to adjust the time constant of the filter to a small value with some margin. , especially when the frequency is low, there is no such margin and it has not been possible to solve the problem of the time it takes for the signal to reach its final value after changing the range as mentioned above. Therefore, the present invention has been made in view of the above-mentioned problems, and its purpose is to shorten the time it takes for the output to converge to the final value after range switching, thereby speeding up the measurement and ensuring sufficient accuracy. The object of the present invention is to provide a level measuring device that provides stability.

[Means for Solving the Problems] In order to achieve the above object, the level measuring device according to claim 1 according to the present invention includes -11 constant range switching means having a plurality of measurement ranges, and a plurality of low-pass filters having different time constants. , the measurement range is switched and controlled, and when the measurement range is switched, the low-pass filter is selectively switched to a low-pass filter having a time constant smaller than a desired value in conjunction with the switching, and the time constant of the low-pass filter is changed. The present invention is characterized by comprising a control means for controlling switching to a low-pass filter having a desired time constant after a predetermined time determined by has elapsed. Further, the invention of claim 2 provides a measurement range switching means having a plurality of measurement ranges, a plurality of low-pass filters having different time constants, and a sampling means for sampling and outputting the output of the low-pass filter at predetermined time intervals. 2. When switching the measurement range, the low-pass filter is selectively switched to a low-pass filter having a time constant shorter than the sampling time, and after the time constant of the low-pass filter has elapsed, It is characterized by a control means that controls switching to a low-pass filter whose constant has an appropriate value. Furthermore, the invention of claim 3 provides a measurement range switching means having a plurality of measurement ranges, a plurality of low-pass filters having different time constants, and a sampling means for sampling and outputting the output of the low-pass filter at predetermined time intervals. The measurement range is switched and controlled, and when the measurement range is switched, the low-pass filter is selectively switched to a low-pass filter with a time constant smaller than an appropriate value, and after the time constant of the low-pass filter has elapsed, the time constant is changed. The present invention is characterized by comprising a control means for controlling switching to a low-pass filter having an appropriate value, and a maximum value storage means for updating and storing a maximum value every sampling time of the sampling means.

[Function] If the measurement range is changed and switched while measurement is being performed in a certain measurement range, the low-pass filter is selectively switched to a low-pass filter with a time constant smaller than the appropriate value. Then, when a predetermined time determined by the time constant of this low-pass filter has elapsed, the time constant is switched to a low-pass filter with a desired (appropriate value) and measurement is performed. Here, from the time the measurement range is switched until the output converges to the final value, it is possible to selectively switch to a low-pass filter with the smallest time constant or a low-pass filter with a time constant shorter than the signal sampling time. ．． Furthermore, the signal output through the selectively switched low-pass filter is sampled at predetermined time intervals, and the maximum value is updated and stored at each sampling time.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of a level measuring device according to the present invention. The level measuring device according to this embodiment converges the level of the finally output signal ('W1 pressure) to a predetermined level range by switching the measurement range, and includes a measurement range switching means l, a low-pass filter 2, a level Measuring section 3, ill+fixed range determining section 4. Filter control section 5, filter switching section 6
, sampling section 7, maximum value storage section 8, data conversion section 9
, a display section 10. The variable gain amplifier 1 as a measurement range switching means amplifies the final output to an appropriate value, and is provided with a plurality of measurement ranges la whose amplification degree can be varied in order to amplify the input signal by a predetermined amount and output it. ．． Specifically, as shown in FIG. 2, a plurality of feedback resistors R forming a measurement range la are connected in parallel to an amplifier A. The low-pass filter 2 has a common capacitor C through which signals are charged and discharged, and resistors rl and r2 (rl
>r2) are connected in series between the capacitor C and the amplifier A via the filter switching unit 6 to constitute a first low-pass filter 2a and a second robust filter 2b. Here, the first low-pass filter 2a is for obtaining sufficient stability, and is set to an optimal time constant according to the measuring range la, and the second low-pass filter 2b is set so that the output is the final value. The time constant is set to be smaller than that of the first low-pass filter 2a. When a signal is supplied from the variable gain amplifier l, each of the filters 2a and 2b outputs the signal according to its time constant. The level measuring section 3 converts the final output into a measured value,
The level of the signal from the low-pass filter 2 is measured and the results are output to the measurement range determining section 4 and the sampling section 7. The measurement range determination unit 4 outputs a switching signal Sl to the variable gain amplifier l so that the optimum measurement range la is selected based on the output from the level measurement unit 3, and the variable gain amplifier I is controlled by the switching signal sl. Measuring range la is being switched. Further, the measurement range determination section outputs the current signal level state and the result of whether or not the switching signal SL is output (whether or not the measurement range 1a is switched) to the filter control section 5 as a determination signal S2. The filter control unit 5 outputs a switching signal S3 to the filter switching unit 6 based on the determination signal S2 from the measurement range determining unit 4, and the filter switching unit 6 uses the switching signal S3 to switch between the variable gain amplifier 1 and each low-pass filter. Switching control between 2a and 2b is performed. To explain further, as shown in FIG.
The time it takes for the first low-pass filter 2 to switch is
Switching is controlled so that a is selected. The sampling section 7 samples the output from the level measuring section 3 at every predetermined sampling time T as shown in FIG. 4, and stores the results in the maximum value storage section 8 and the data conversion section 9.
It is output to . The maximum value storage section 8 constantly updates and stores the maximum value of the sampling data sequentially supplied from the sampling section 7. The data conversion section 9 converts the sampling data sequentially supplied from the sampling section 7 into display signals, and displays the data numerically on the display section 10 in real time. Next, we will explain the operation of the level measuring device configured as above.
This will be explained based on the flowchart shown in FIG. When a measurement is being performed in a certain measurement range la (S
TI). If the output deviates from the current measurement range and becomes overrange or underrange (ST2
-Yes). It is switched to the measurable measurement range la by the switching signal si from the fixed range determination section 4 (
ST3). When this range switching is performed, the second low-pass filter 2b is selected by the switching signal S3 from the filter control section 5 (ST4). A signal is outputted and measured according to the time constant of this filter 2b. When the output converges to the final value after a time t based on the time constant of the filter 2b has elapsed, the low-pass filter 2a of il is selected by the switching signal S3 from the filter control section 5 (ST5). A signal is output according to the time constant of the filter 2a and measurement is performed (ST6
). During the above-mentioned operation, the signals output from each filter 2a, 2b are measured by the level measuring section 3, and then sampled every time T, and the maximum value each time is stored in the maximum value storage section 8 and displayed. The numerical value is displayed in section 10. Here, FIG. 4 shows the output with respect to the sampling time in each of the present embodiment and the conventional level regulator. As is clear from this figure, in the conventional level measuring device, as shown by the broken line in the figure, it takes a time t1 longer than the sampling time T to converge to the final value after the measurement range is switched, and the response is slow. Since it is slow, the intermediate values in the transient state until it converges to the final value are taken as sampling data, and the incorrect maximum value is displayed. As a result, the data displayed on the display screen of the display unit changes many times before it settles down to the final value, so the user cannot read the intermediate value data displayed on the display screen in a transient state. There was a risk of mistaking it as the maximum value. In addition, to solve this problem, the signal convergence time 1. If a sufficient sampling time T is taken for this, a problem arises in that the corresponding measurement time is required, making it impossible to perform efficient measurements. In contrast, in this embodiment, the time from when the measurement range is switched to when the measurement range converges on the final value is processed by the second low-pass filter 2b with a small time constant. Until the measurement range is switched, the signal is processed by the first low-pass filter 2a, which is set to the optimal time constant that provides stability, so the time from when the measurement range is switched until convergence to the final value is t
2 is shorter than the sampling time T, the response is fast, and the final value can be obtained in an extremely short time, so the accurate maximum (l
M (final value) can be stored and displayed, allowing the user to always know the correct maximum value and preventing misidentification. Furthermore, since the accurate maximum value can always be measured and stored in this way, when applied to an optical power meter, it is possible to measure the optimal optical axis alignment position. In addition, by measuring the level of the signal supplied to each p1m measurement object, it can be applied to evaluation tests of objects to be measured. Figure 6 shows the measurement results when the level measuring device described above is applied to an optical power meter. As is clear from this figure, in any of the states (11 to (3)), the time from switching the measurement range to convergence to the final value is faster in this embodiment than in the conventional one. Furthermore, since the time constant of the low-pass filter is set large when changing the range in a state that contains a lot of noise as in (1) and (2), the time constant of the conventional filter is The convergence time becomes longer as the constant is increased, and the time difference from this example is noticeable.In addition, the stability of the measured output is at the same level as the one equipped with the diode shown in Figure 9. ±0.06dB with measuring instrument
On the other hand, in this example, it is even more stable at ±0.04 dB. Therefore, in the above-mentioned embodiment, the time from switching the measurement range to convergence to the final value is shortened as described above, so the overall measurement time is shortened, making it more efficient in a short time when there are many objects to be measured. It is possible to carry out specific measurements. In addition, even if the time constant of the low-pass filter is increased in order to reduce the response speed, reduce noise and fluctuations, and increase stability, the switching speed of the dramatic range does not change as described above. It is possible to perform accurate and high-speed measurements. Furthermore, in this practical example, the final value is obtained in a shorter time than the sampling time, and the maximum value of the sampling data is updated and stored at each sampling time, so the user can quickly obtain the accurate maximum value after switching the measurement range. You can check. Furthermore, by applying this function to optical axis alignment in optical power meters, evaluation tests of objects to be measured, etc., more efficient measurements can be made. By the way, in the above-mentioned embodiment, the case where the signal supplied to the variable gain amplifier is a DC signal was explained as an example.
As shown in FIG. 7, a light emitting section 11a. An AC signal output circuit i. t, and a filter l2 and an optical chopper section 1l are provided after the variable gain amplifier l.
By providing a detection section 13 that is synchronized with b, the present invention can also be applied to level measuring instruments that handle alternating current signals. Therefore, AC signals can be detected like synchronous detection. Even when measuring that signal, it is possible to increase the switching speed of the measurement range without having to do with the response speed of the low-pass filter as in the past. In addition, in the above-mentioned embodiment, the configuration was explained using two low-pass filters with different time constants, but in order to obtain sufficient stability, low-pass filters with different time constants are provided for each of several measurement ranges. A plurality of filters may be provided, in which case the filters are used from the time the measurement range is switched until the final value is reached. i! The filter is selectively switched to a filter with a time constant smaller than the positive value of I, a filter with the minimum time constant, or a filter with a time constant shorter than the sampling time. [Effects of the Invention] As explained above, according to the level measuring device according to claims 1 and 2 of the present invention, the time required for convergence to the final value of R after range switching can be shortened, thereby speeding up the measurement. , sufficient stability of the output at that time is ensured. Also, even if you increase the time constant of the low-pass filter to reduce the response speed, reduce the effects of noise and fluctuation, and increase stability,
Since the measurement range switching speed does not change, high-accuracy and high-speed measurements can be performed. Further, according to the level measuring device according to claim 3 of the present invention,
The final value is obtained in a shorter time than the sampling time, and the maximum value of the sampling data is updated and stored at each sampling time, so the user can check the accurate maximum value in a short time after switching the measurement range. If the function is applied to optical axis alignment in an optical power meter, evaluation test of a measured object, etc., even more efficient measurements can be performed.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the level measuring device according to the present invention, FIG. 2 is a diagram showing a specific example of the configuration of the variable gain amplifier, filter switching section, and low-pass filter in FIG. 1, and FIG. 4 is a diagram showing the output versus time when switching ranges, FIG. 4 is a diagram showing the output versus sampling time in both the present invention and the conventional level measuring device, and FIG. 5 is a flowchart showing the operation of the level measuring device according to the present invention. 6 are diagrams showing an example of measurement results when the same measuring device is applied to an optical power meter, FIG. 7 is a block diagram showing another embodiment of the level measuring device according to the present invention, and FIG. Figure 9 is a diagram showing an example of a conventional level measuring device. 1... Variable gain amplifier (measurement range switching means), 1a... Measurement range, 2 (2a, 2
b)...Low pass filter, 3...Level measuring section,
4.--Measurement range determination section, 5.--Filter control section, 6
... Filter switching section, 7... Sampling section, 8.
...Maximum value storage section.

Claims (3)

[Claims] (1) Measurement range switching means having a plurality of measurement ranges, a plurality of low-pass filters having different time constants, controlling the switching of the measurement ranges, and controlling the switching of the measurement ranges in conjunction with the switching. control means for selectively switching to a low-pass filter with a time constant smaller than a desired value, and controlling switching to the low-pass filter having a desired time constant after a predetermined time determined by the time constant of the low-pass filter has elapsed; Characteristic level measuring device. (2) A measurement range switching means having a plurality of measurement ranges, a plurality of low-pass filters having different time constants, a sampling means for sampling and outputting the output of the low-pass filter at predetermined time intervals, and controlling the switching of the measurement ranges. At the same time, when switching the measurement range, the low-pass filter is selectively switched to a low-pass filter having a time constant shorter than the sampling time, and after the time constant of the low-pass filter has elapsed, the low-pass filter with a time constant of an appropriate value is switched. A level measuring device characterized by comprising: control means for controlling switching to a filter. (3) A measurement range switching means having a plurality of measurement ranges, a plurality of low-pass filters having different time constants, a sampling means for sampling and outputting the output of the low-pass filter at predetermined time intervals, and controlling the switching of the measurement ranges. At the same time, when switching the measurement range, the low-pass filter is selectively switched to a low-pass filter with a time constant smaller than the appropriate value, and after a time period according to the time constant of the low-pass filter has elapsed, the low-pass filter has a time constant of the appropriate value. A level measuring device comprising: control means for controlling switching; and maximum value storage means for updating and storing a maximum value every sampling time of the sampling means.