JPH0830659B2 - Level measuring instrument - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a level measuring device that converges a finally output signal level into a predetermined level range by switching a measurement range.

[Prior Art] For example, in a measuring instrument, several measurement ranges are provided so that the level of a signal finally output converges to a predetermined level range in order to increase the signal processing speed and a wide dynamic range. A method is used in which the measurement ranges are automatically switched one by one, thereby measuring signals within a certain range.

In this case, the input signal is a sine wave or a rectangular wave, and a low pass filter is required to detect the signal and convert it into a stabilized DC signal.

FIG. 8 shows a schematic structure of a level measuring instrument using such a low pass filter.

In this level measuring instrument, feedback resistors r forming a plurality of measuring ranges 21 are connected in parallel to an amplifier 20.
A low-pass filter 22 consisting of a resistor R and a capacitor C is connected in series in the subsequent stage, and when the measurement range 21 is switched according to the input signal, its output is timed according to the time constant of the low-pass filter as shown in FIG. It changes to the final value over t ₁ .

[Problems to be Solved by the Invention] However, in the above-mentioned conventional level measuring instrument, it takes t ₁ time after the switching of the measuring range 21 until the output converges to the final value. There was a problem of slowing down the measurement speed.

Therefore, in order to solve the above-mentioned problem, the time constant of the low-pass filter is made small, or as shown in FIG. 9, the diode D is connected in parallel with the resistor R constituting the low-pass filter 22 to discharge the capacitor C. To speed up the measurement speed.

However, such a method has a problem that the signal cannot be sufficiently smoothed and stability is deteriorated.

On the other hand, in the measurement of the optical power level by the optical power meter, the above-mentioned level measuring device is used in order to eliminate the influence of the drift of the photodetector and achieve high sensitivity and enable measurement to a low level.

In this case, the signal is treated as an 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 to smooth this detected signal sufficiently, a certain time constant is required. A low pass filter with is required.

By the way, when setting the time constant of the low-pass filter to sufficiently smooth the signal, if the frequency of the signal to be handled is high, it is possible to adjust the time constant of the filter to some extent with a margin, but especially the frequency In the case of low, there is no such margin, and as described above, the problem that it takes time for the signal to reach the final value after range switching cannot be solved.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object thereof is to shorten the time until the output converges to the final value after the range is switched and to achieve a high-speed measurement with sufficient accuracy. It is to provide a level measuring instrument that can obtain stability.

[Means for Solving the Problems] In order to achieve the above object, the level measuring instrument according to claim 1 of the present invention comprises a measurement range switching means having a plurality of measurement ranges, 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 association with the switching, and is determined by the time constant of the low pass filter. A control means for controlling switching to a low-pass filter having a desired time constant after a lapse of a predetermined time is provided.

The invention according to claim 2 further comprises a measurement range switching means having a plurality of measurement ranges, a plurality of low-pass filters having different time constants, and sampling means for sampling and outputting the output of the low-pass filters at predetermined time intervals. While controlling the switching of the measurement range, the low-pass filter is selectively switched to a low-pass filter having a time constant shorter than the sampling time at the time of switching the measurement range, and the time is passed after the time according to the time constant of the low-pass filter has elapsed. And a control means for controlling the switching to a low-pass filter having an appropriate constant value.

Furthermore, the invention of claim 3 is 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 filters at predetermined time intervals, While switching control of the measurement range, at the time of switching of the measurement range, the low-pass filter is selectively switched to a low-pass filter having a time constant smaller than an appropriate value, and the time constant after the time due to the time constant of the low-pass filter has elapsed. The present invention is characterized by comprising control means for switching control to a low-pass filter having an appropriate value, and maximum value storage means for updating and storing the maximum value at each sampling time of the sampling means.

[Operation] When the measurement range is changed and switched while being measured in a certain measurement range, the low pass filter is selectively switched to a low pass filter having a time constant smaller than an appropriate value. Then, when a predetermined time determined by the time constant of the low pass filter has elapsed, the time constant is switched to a desired (appropriate value) low pass filter and measurement is performed.

Here, during the period from the switching of the measurement range to the convergence of the output to the final value, it is possible to selectively switch to a low-pass filter having a minimum time constant or a time constant shorter than the sampling time of the signal. ..

Further, the signal output through the selectively switched low-pass filter is sampled every predetermined time, and the maximum value is updated and stored every 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 (voltage) into a predetermined level range by switching the measuring range, and the measuring range switching means 1, the low-pass filter 2 and the level measuring section. 3, a measurement range determination unit 4, a filter control unit 5, a filter switching unit 6, a sampling unit 7, a maximum value storage unit 8, a data conversion unit 9, and a display unit 10.

The variable gain amplifier 1 as the measurement range switching means amplifies the final output to an appropriate value, and is provided with a plurality of measurement ranges 1a with variable amplification degrees so as 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 1a with respect to the amplifier A are provided.
Are connected in parallel.

The low-pass filter 2 has a common capacitor C for charging / discharging signals, and resistors r1 and r2 (r1> r2) connected in parallel.
Are connected in series between the capacitor C and the amplifier A via the filter switching unit 6 to connect the first low-pass filter 2a and the second low-pass filter 2a.
Of the low pass filter 2b.

Here, the first low-pass filter 2a is for obtaining sufficient stability and is set to an optimum time constant according to the measurement range 1a, and the second low-pass filter 2b reaches the final value of the output. The response time is up to, and the time constant is set smaller than that of the first low pass filter 2a. When a signal is supplied from the variable gain amplifier 1 to each of the filters 2a and 2b, the signal is output according to the time constant.

The level measuring unit 3 converts the final output into a measured value. The level measuring unit 3 measures the level of the signal from the low pass filter 2 and outputs the measurement result to the measurement range determining unit 4 and the sampling unit 7.
Is output to.

The measurement range determination unit 4 outputs the switching signal S1 to the variable gain amplifier 1 so that the optimum measurement range 1a is selected based on the output from the level measurement unit 3.
Switches the measurement range 1a by this switching signal S1. In addition, the result of the level condition of the current signal from the measurement range determination unit and the output of the switching signal S1 (whether the measurement range 1a is switched) is used as the determination signal S2 as the filter control unit 5
Is output to.

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 determination unit 4, and the filter switching unit 6 uses the switching signal S3 to output the variable gain amplifier 1 and each low-pass filter. Switching control between 2a and 2b is performed. More specifically, as shown in FIG. 3, the time t ₂ from the switching of the measurement range 1a to the convergence of the output to the final value is the second low-pass filter 2b.
However, after that, the switching time is controlled so that the first low-pass filter 2a is selected until the next measurement range 1a is switched.

The sampling unit 7 outputs the output from the level measuring unit 3 to the fourth
As shown in the figure, sampling is performed at every predetermined sampling time T and the result is output to the maximum value storage unit 8 and the data conversion unit 9.

The maximum value storage unit 8 constantly stores and updates the maximum value of the sampling data sequentially supplied from the sampling unit 7.

The data conversion unit 9 converts the sampling data sequentially supplied from the sampling unit 7 into a display signal, and numerically displays the data on the display unit 10 in real time.

Next, the operation of the level measuring instrument configured as described above will be described with reference to the flow chart shown in FIG.

When measurement is being performed in a certain measurement range 1a (ST
1) If the output goes out of the current measurement range range and becomes overrange or underrange (ST2-Ye
s), the measurement range 1a is switched to the measurable measurement range 1a by the switching signal S1 from the measurement range determination unit 4 (ST3). When this range switching is performed, the switching signal from the filter controller 5
The second low-pass filter 2b is selected by S3 (ST
4), a signal is output according to the time constant of this filter 2b and measurement is performed. Then, when the time t ₂ based on the time constant of the filter 2b elapses and the output converges to the final value, the switching signal S3 from the filter control unit 5 selects the first low-pass filter 2a (ST5), A signal is output according to the time constant of the filter 2a and measurement is performed (ST6).

During the operation described above, the signals output from the filters 2a and 2b are measured by the level measuring unit 3 and then sampled at each time T, and the maximum value is stored in the maximum value storage unit 8 at each time and displayed. Numerical value is displayed on part 10.

Here, FIG. 4 shows the output with respect to the sampling time in each of the level measuring instrument of the present embodiment and the conventional level measuring instrument.

As is clear from this figure, the conventional level measuring instrument requires a time t ₁ longer than the sampling time T from the measurement range is switched to the final value as shown by the broken line in the figure, and the response is required. Is slow, the intermediate value in the transient state until it converges to the final value is taken as sampling data, and the incorrect maximum value is displayed. As a result, since the data displayed on the display screen of the display unit changes many times before reaching the final value data, the user can change the intermediate value data in the transient state displayed on the display screen. There was a risk of mistakenly recognizing it as the maximum value. Further, if a sufficient sampling time T is set for the signal convergence time t ₁ in order to solve this problem, there arises a problem that the measurement time is correspondingly required and efficient measurement cannot be performed.

On the other hand, in this embodiment, the time t ₂ from the switching of the measurement range to the convergence to the final value is processed by the second low-pass filter 2b having a small time constant, converges to the final value, and then The signal is processed by the first low-pass filter 2a that is set to the optimum time constant that provides stability until switching to the measurement range, so the time from when the measurement range is switched until it converges to the final value. Since 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, the accurate maximum value (final value) can always be stored and displayed. It is possible to know the value and prevent misidentification.

In addition, since an accurate maximum value can always be measured and stored in this way, when applied to an optical power meter, the optimum optical axis alignment position can be measured. In addition, by measuring the level of a signal supplied to various measured objects, it can be applied to an evaluation test of the measured objects.

Here, FIG. 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 (1) to (3), the time from the switching of the measurement range to the convergence to the final value is higher in the present embodiment than in the conventional one. I understand that. Furthermore, (1),
Since the range switching in the state containing a lot of noise as in (2) uses a large time constant of the low-pass filter,
In that case, in the conventional case, the convergence time becomes longer corresponding to the state in which the time constant is made larger, and the time difference from the present embodiment appears significantly.

Further, the stability of the measured output is ± 0.06 dB in the level measuring instrument equipped with the diode shown in FIG. 9 and ± 0.04 dB in the present embodiment, which is more stable.

Therefore, in the above-described embodiment, since the time from the switching of the measurement range to the convergence to the final value is shortened as described above, the overall measurement time is shortened and the efficiency is reduced in a short time when there are many measured objects. Measurements can be performed.

In addition, even if the time constant of the low-pass filter is increased to decrease the response speed to reduce the influence of noise and fluctuations and increase the stability, the switching speed of the measurement range does not change as described above, so it is highly accurate. Moreover, high-speed measurement can be performed.

Further, in this embodiment, the final value is obtained in a time shorter than the sampling time, and the maximum value of the sampling data is updated and stored for each sampling time, so that the user can obtain the accurate maximum value in a short time after switching the measurement range. You can check. Further, if this function is applied to optical axis alignment in an optical power meter, evaluation test of an object to be measured, etc., more efficient measurement can be performed.

By the way, in the above-described embodiment, the case where the signal supplied to the variable gain amplifier is a DC signal has been described as an example. However, as shown in FIG. An AC signal signal output circuit 11 including a light receiving unit 11c is provided, and a detection unit 1 that synchronizes with a filter 12 and an optical chopper unit 11b is provided at a subsequent stage of the variable gain amplifier 1.
By providing 3, it can be applied to a level measuring instrument that handles an AC signal.

Therefore, even when the AC signal is detected and the signal is measured as in the case of synchronous detection, the speed of switching the measurement range can be increased regardless of the response speed of the low-pass filter as in the conventional case.

Further, in the above-described embodiment, the configuration provided with two low-pass filters having different time constants has been described as an example, but in order to obtain sufficient stability, low-pass filters having different time constants are associated with several measurement ranges. Multiple filters may be provided.In this case, from the time the measurement range is changed to the final value, a filter with a time constant smaller than an appropriate value, a filter with a minimum time constant, and a filter with a time constant shorter than the sampling time are used. The filter is selectively switched and controlled.

[Effects of the Invention] As described above, according to the level measuring instrument according to the first and second aspects of the present invention, it is possible to shorten the time until it converges to the final value after the range is switched and to speed up the measurement. , The output at that time has a sufficient stability. Also, even if the time constant of the low-pass filter is increased to decrease the response speed to reduce the influence of noise and fluctuations and increase the stability, the switching speed of the measurement range does not change, so high-accuracy and high-speed measurement is possible. Can be done.

Further, according to the level measuring instrument of claim 3 of the present invention, the final value can be obtained in a time shorter than the sampling time,
Since the maximum value of the sampling data is updated and stored for each sampling time, the user can confirm the accurate maximum value in a short time after switching the measurement range. If it is applied to an evaluation test of a product, more efficient measurement can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a level measuring device according to the present invention, and FIG. 2 is a diagram showing a concrete example of the configuration of a variable gain amplifier, a filter switching unit and a low-pass filter in FIG. 1, and FIG. Is a diagram showing the output with respect to time when the range is switched, FIG. 4 is a diagram showing the output with respect to the sampling time in each of the present invention and the conventional level measuring instrument, and FIG. 5 is a flowchart showing the operation of the level measuring instrument according to the present invention. FIG. 6 is a diagram 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. And FIG. 9 is a diagram showing an example of a conventional level measuring instrument. 1 ... Variable gain amplifier (measurement range switching means), 1a ...
Measurement range, 2 (2a, 2b) ... Low-pass filter, 3 ...
... Level measuring unit, 4 ... Measurement range determining unit, 5 ... Filter control unit, 6 ... Filter switching unit, 7 ... Sampling unit, 8 ... Maximum value storage unit.

Claims (3)

[Claims] 1. A level at which a low-pass filter for converting the AC signal into DC is switched when the measurement range is switched in correspondence with the magnitude of the voltage level of an input AC signal. In the measuring instrument, a measurement range switching means having a plurality of measurement ranges, a plurality of low-pass filters having different time constants, switching control of the measurement ranges, and at the time of switching the measurement ranges, the low-pass filter is interlocked with the switching. And a control means for selectively switching to a low-pass filter having a time constant smaller than a desired value, and switching control to a low-pass filter having a desired time constant after a lapse of a predetermined time determined by the time constant of the low-pass filter. A level measuring instrument characterized by. 2. A level at which a low-pass filter for converting the AC signal into DC is switched when the measurement range is switched in correspondence with the magnitude of the voltage level of an input AC signal. In the measuring device, 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 filters at predetermined time intervals, and switching the measurement range. While controlling, 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 the time constant of the low-pass filter has a proper value after a lapse of time. A low-pass filter, and a control means for switching control. Le measuring instrument. 3. A level at which a low-pass filter for converting the AC signal into DC is switched when the measurement range is switched in correspondence with the magnitude of the voltage level of the input AC signal. In the measuring device, 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 filters at predetermined time intervals, and switching the measurement range. Along with controlling, the low-pass filter selectively switches to a low-pass filter having a time constant smaller than an appropriate value in the low-pass filter at the time of switching the measurement range, and the time constant of the low-pass filter elapses after a lapse of the time constant. Control means for switching control to, and for each sampling time of the sampling means A level measuring instrument comprising: a maximum value storage means for updating and storing the maximum value.