JPH11160017A - Length measuring laser apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a length measuring laser apparatus capable of correcting position information at the time of reading the posit ion information. SOLUTION: In a laser length measuring apparatus using heterodyne interference, a receiver 1 which receives an interference light 100 and outputs an interference signal, a position measuring circuit 2a which measures position information on the basis of a reference signal 101 converted into a voltage signal from the difference of two frequencies and the interference signal, end a position correcting circuit 3 which corrects position information at the time of reading the position information by obtaining and adding an estimated traveling distance after period measurement, on the basis of the output of the position measuring circuit 2a are installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser length measuring device using heterodyne interference, and more particularly to a laser length measuring device capable of correcting a position at the time of reading position information.

[0002]

2. Description of the Related Art A conventional laser length measuring apparatus using heterodyne interference uses laser beams of two frequencies, one of which is a reference mirror, and the other is a mirror attached to an object to be measured. Each is reflected and interfered.

When the DUT moves, the frequency of the interference light when the DUT moves changes compared to the frequency of the interference light when the DUT stops due to the Doppler effect.

Therefore, by using the frequency of the difference between the two frequencies as a reference signal and detecting the phase difference between this reference signal and the interference light when the device under test moves, the position of the device under test from its initial state is detected. The change, in other words, the position of the measured object can be measured.

FIG. 8 is a block diagram showing an example of such a conventional laser length measuring apparatus. In FIG. 8, reference numeral 1 denotes a receiver, 2 denotes a phase measurement circuit, 100 denotes interference light, and 101 denotes a reference signal obtained by converting the difference between the two frequencies into a voltage signal.

[0006] The interference light 100 enters the receiver 1, and the output of the receiver 1 is connected to the phase measurement circuit 2. Also,
The reference signal 101 is also connected to the phase measurement circuit 2.

Here, the operation of the conventional example shown in FIG. 8 will be described. The receiver 1 receives the interference light 100 and amplifies it as appropriate.
It is converted into a digital signal and output as an interference signal.

The phase measuring circuit 2 appropriately multiplies the reference signal 101 to generate a clock signal, counts the period of the interference signal output from the receiver 1 based on the clock signal, and, based on the count value, corresponds to the period of the reference signal 101. The phase difference is obtained by subtracting the count value to be counted. The phase measurement circuit 2 sequentially integrates the phase differences.

Since this phase difference means the distance that the device under test moves in one cycle of the reference signal, the relative distance from the initial state of the device under test is calculated by successively integrating the moving distances in one cycle. It becomes possible to obtain the position.

[0010]

However, in the conventional laser length measuring device, the phase difference is obtained by measuring the period of the interference signal, so that the position information output from the phase measuring circuit 2 is measured at any time. I don't know if it is the location information.

For example, FIG. 9 is a timing chart showing an example of the cycle measuring operation. FIG. 9A shows a reference signal, and FIG.
Is an interference signal, (c) timing of period measurement, and (d) position information to be read.

When measuring the periods of the interference signals indicated by "a", "b", "c", "d" and "e" in FIG.
The cycle counting operation or the like ends at the timing of middle "he", "g", "h", "ri", and "nu".

The position information is synchronized with the reference signal,
Specifically, it is read at the rising timing of the reference signal.

However, since it takes a long time to calculate the phase difference and the like, for example, the position information obtained from the period indicated by "A" in FIG. 9 can be read only at the time of "R" in FIG. I can do it.

That is, the position information obtained from the period of the interference signal indicated by “A” in FIG.
The output is performed after the time indicated by “ヲ”. In other words, since the device under test continues to move for the time indicated by “ヲ” in FIG. 9, the read position information is different from the actual position information. Has become.

Further, FIG.
Since the time indicated by the middle "ヲ" also fluctuates, it is difficult to simply correct the position information.

For this reason, when a position control loop is formed by using a laser length measuring device, it is difficult to optimize the control loop because the read position information cannot be specified at which point of time. was there. Accordingly, an object of the present invention is to realize a laser length measuring device capable of correcting position information at the time of reading position information.

[0018]

According to a first aspect of the present invention, there is provided a laser length measuring apparatus using heterodyne interference, comprising a receiver for receiving an interference light and outputting an interference signal. A position measuring circuit for measuring position information based on a reference signal obtained by converting the frequency of the difference between the two frequencies into a voltage signal and the interference signal, and obtaining an estimated moving distance after period measurement based on an output of the position measuring circuit. And a position correction circuit for correcting the position information at the time of reading the position information by adding the position information.

According to a second aspect of the present invention, in the second aspect of the present invention, in the first aspect of the present invention, the position measuring circuit measures a period of the interference signal based on the reference signal, thereby obtaining the position information. And the time from the period measurement to the first readout timing is measured.

In order to achieve the above object, according to a third aspect of the present invention, in the second aspect of the present invention, the period of the interference signal is counted based on the reference signal.

In order to achieve the above object, according to a fourth aspect of the present invention, in the second aspect of the present invention, the position correction circuit is configured to determine the period of the interference signal and the reference signal and the first read timing after measuring the period. The estimated moving distance after the period measurement is obtained based on the time up to.

In order to achieve the above object, according to a fifth aspect of the present invention, in the third aspect of the present invention, the position correction circuit is configured to measure the period of the interference signal and the reference signal, the value of the count, and And calculating the estimated moving distance after period measurement based on the time from the first reading timing to the first reading timing.

In order to achieve the above object, a sixth aspect of the present invention is directed to the first aspect of the present invention, wherein an arithmetic control circuit having a function of the position measuring circuit and a function of the position correcting circuit is provided. It is a feature.

According to a seventh aspect of the present invention, there is provided a laser length measuring apparatus using heterodyne interference, comprising: a receiver for receiving an interference light and outputting an interference signal; A position measuring circuit for measuring position information based on a reference signal obtained by converting the frequency of the voltage into a voltage signal and the interference signal, and an estimated moving distance after period measurement in which a circuit delay due to an input frequency is corrected based on an output of the position measuring circuit. And a position correction circuit that corrects the position information at the time of reading the position information by calculating and adding the position information.

In order to achieve the above object, according to an eighth aspect of the present invention, in the seventh aspect of the present invention, the position information circuit measures the period of the interference signal based on the reference signal, thereby obtaining the position information. And the time from the period measurement to the first readout timing is measured.

In order to achieve the above object, according to a ninth aspect of the present invention, in the eighth aspect of the present invention, the period of the interference signal is measured based on the reference signal.

In order to achieve the above object, in a tenth aspect of the present invention, in the eighth aspect of the present invention, the position / delay correction circuit sets a circuit delay of the time from the period measurement to the first read timing. The estimated moving distance after the period measurement is obtained based on the period from the period after the period of the interference signal and the reference signal and the period after the delay correction is corrected to the first readout timing.

In order to achieve the above object, according to an eleventh aspect of the present invention, in the ninth aspect of the present invention, the position / delay correction circuit sets a circuit delay of the time from a period measurement to a first read timing. Correcting the period of the interference signal and the reference signal, the value of the count and the time from the delay-corrected period measurement to the first readout timing to obtain the estimated moving distance after the period measurement based on the time. Is what you do.

In order to achieve the above object, according to a twelfth aspect of the present invention, in the seventh aspect of the present invention, there is provided an arithmetic control circuit having a function of the position measuring circuit and a function of the position / delay correcting circuit. It is characterized by the following.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration block diagram showing an embodiment of a laser length measuring apparatus according to the present invention.

In FIG. 1, 1, 100 and 101 correspond to FIG.
2a is a phase measurement circuit, 3 is a position correction circuit, 102 is a periodic signal, 103 is a count signal, and 104 is a time signal from the period measurement to the first readout timing (hereinafter simply referred to as time). Signal) .10
5 is an integrated position information signal, and 106 is a corrected position information signal.

The interference light 100 enters the receiver 1, and the output of the receiver 1 is connected to the phase measuring circuit 2a. The reference signal 101 is also connected to the phase measurement circuit 2a.

The period signal 102, the count signal 103, the time signal 104, and the position information signal 10 of the phase measurement circuit 2a
5 are connected to the position correction circuit 3, and the position correction circuit 3 outputs a corrected position information signal 106.

The operation of the embodiment shown in FIG. 1 will now be described with reference to FIGS. FIG. 2 is a timing chart showing the relationship between the interference signal, the reference signal, and the time from the period measurement to the first readout timing, and FIG. 3 is a flowchart showing a position correction calculation method.

The receiver 1 receives the interference light 100, amplifies it appropriately, binarizes it, converts it into a digital signal, and outputs it as an interference signal.

The phase measuring circuit 2a measures the period of the interference signal and subtracts the period of the reference signal 101 from the measured value to determine the phase difference. Further, the phase measurement circuit 2a sequentially integrates this phase difference.

The phase measuring circuit 2a sends the periodic signal 102 indicating the latest cycle of the interference signal, the count signal 103 indicating the count value in the phase measuring circuit 2a, the time signal 104 and the position information signal 105 to the phase correcting circuit 3, respectively. Output.

The phase correction circuit 3 calculates and outputs a corrected position information signal 106 at the time of reading based on these signals.

For example, when the period shown in FIG. 2A is measured, it is not possible to read out at least the timing shown in FIG.

That is, in this case, since the time indicated by "c" in FIG. 2 has elapsed since the end of the cycle measurement, the position corrected by the movement during this time is corrected.

When the period of the interference signal is longer than the period of the reference signal indicated by "d" in FIG. 2, as indicated by "e" in FIG. The position information is read out at the timings shown in "H", "LI" and "NU" in FIG. 2 until the measurement of the next measurement period shown in "G" in FIG. It is.

In this case, the position information read at the timing indicated by "h" in FIG. 2 corresponds to the time indicated by "c" in FIG. 2 and the time corresponding to one reference signal period indicated by "d" in FIG. It is necessary to correct the position of the moving part.

Similarly, in the case of "Li" or "Nu" in FIG. 2, it moves to the time indicated by "C" in FIG. 2 plus two or three reference signal periods indicated by "D" in FIG. It is necessary to correct the position.

That is, the elapsed time is corrected by adding “count value × reference signal period” to the time indicated by “c” in FIG.

As shown in FIGS. 3 (a), 3 (c), 3 (d) and 3 (e), the position correction circuit 3 sends a periodic signal 102, a count signal 103, a time signal 104 and a position information signal 105 from the phase measuring circuit 2a. Respectively. FIG.
The cycle of the reference signal shown in (b) is set in advance.

As shown in FIG. 3 (f), the position correction circuit 3 changes the cycle of the reference signal from the latest cycle "T" to the cycle "Tr" of the reference signal.
ef "is subtracted from the phase difference, in other words," a "in FIG.
Is determined as d = T-Tref (1).

Further, as shown in FIG. 3G, the position correction circuit 3 obtains the elapsed time “t1” after the period measurement based on the count signal 103 and the time signal 104. Here, assuming that the count value is “Sc” and the time indicated by “c” in FIG. 2 is “t”, t1 = t + (Tref × Sc) (2)

Next, as shown in FIG. 3H, the position correction circuit 3 calculates the ratio of the elapsed time after the period measurement to the latest measured period, {t + (Tref × Sc)} / T (3) And ask.

Further, as shown in FIG. 3 (i), the position correction circuit 3 calculates the estimated moving distance “d1” after the period measurement from the equations (1) and (3) as follows: d1 = (T−Tref) × { t + (Tref × Sc)} / T (4)

Finally, as shown in FIG. 3 (j), the position correction circuit 3 adds the estimated moving distance after the period measurement obtained by the equation (4) to the position information read in FIG. The information is corrected and output as a corrected position information signal 106.

As a result, the periods of the interference signal and the reference signal,
By obtaining the estimated moving distance after the period measurement based on the count value and the time from the period measurement to the first readout timing, it becomes possible to correct the position information at the time of reading the position information.

Further, the correction of the position information makes it possible to optimize the control loop when a position control loop is formed using a laser length measuring device.

FIG. 4 is a structural block diagram showing details of the receiver 1 and the position measuring circuit 2a. In FIG. 4, 1, 2a, 100 and 101 have the same reference numerals as in FIG. 1, 4 is a photodetector using a photodiode or the like, 5 and 8 are amplifiers, 6 and 9 are filter circuits, 7 and 10 Is a comparator, 11 is a PLL circuit, 12 is a period measurement circuit, 13
Is a counter circuit.

The interference light 100 enters the photodetector 4, and the output of the photodetector 4 is connected to the amplifier 5. The output of the amplifier 5 is connected to a comparator 7 via a filter circuit 6, and the output of the comparator 7 is connected to a period measurement circuit 12.

On the other hand, the reference signal 101 is connected to the amplifier 8, and the output of the amplifier 8 is output via the filter circuit 9 to the comparator 1.
Connected to 0. The output of the comparator 10 is connected to a PLL circuit 11, and the output of the PLL circuit 11 is connected to a period measurement circuit 12. The output of the cycle measuring circuit 12 is connected to the counter circuit 13.

Here, the operation of the detailed block diagram shown in FIG. 4 will be briefly described. The interference light 100 is converted into an electric signal by the photodetector 4 and then appropriately amplified by the amplifier 5. Amplifier 5
Is input to a comparator 7 via a filter circuit 6 and
It is converted into a digital signal and output as an interference signal.

Similarly, the reference signal 101 is appropriately amplified by the amplifier 8, and the output of the amplifier 8 is input to the comparator 10 via the filter circuit 9 to be binarized and converted into a digital signal. It is multiplied and output as a clock signal. Subsequent operations are the same as described above, and a description thereof will be omitted.

At this time, the power “P” of the interference light incident on the photodetector 4 is represented by P = P0 {1 + A · sin2π (f + 2V / λ) · t} (5) Here, “P0” is a DC component, “A” is a ratio of an AC component, “f” is a frequency of a difference between two frequencies,
λ ”is the light wavelength (the two frequencies are close and therefore approximated by the same light wavelength), and“ V ”is the moving speed of the measured object.

From equation (5), the frequency of the interference signal is “f + 2”.
V / [lambda] ", the frequency of the interference signal is" f ± 2V "if the maximum moving speed of the device under test is" Vmax ".
max / λ ”. Therefore, S
In order to improve / N, the filter circuit 6 sets this frequency range as a pass band, and it is better that the attenuation is as large as possible in other frequency ranges.

In order to attenuate noise outside the pass band, a filter having a steep characteristic such as a Chebyshev characteristic may be used as the filter circuit 6, but the circuit delay time due to the input frequency in this pass band is large. There was a problem that it would be different. That is, FIG.
The circuit delay time of the time indicated by the middle "C" varies depending on the input frequency, and the elapsed time after the cycle measurement obtained in FIG. 3G also varies.

FIG. 5 is a block diagram showing the configuration of an embodiment of the laser length measuring apparatus according to the present invention, which takes into account such correction of the circuit delay time. In FIG.
a, 100, 101, 102, 103, 104 and 10
Reference numeral 5 is the same as in FIG. 1, reference numeral 14 is a position / delay correction circuit, and reference numeral 107 is a corrected position information signal.

The interference light 100 enters the receiver 1, and the output of the receiver 1 is connected to the phase measurement circuit 2a. The reference signal 101 is also connected to the phase measurement circuit 2a.

The period signal 102, the count signal 103, the time signal 104, and the position information signal 10 of the phase measurement circuit 2a
5 are connected to the position / delay correction circuit 14, and the position / delay correction circuit 14 outputs a corrected position information signal 107.

The operation of the embodiment shown in FIG. 5 will be described with reference to FIGS. FIG. 6 is a flowchart showing a method of calculating the position correction and the delay correction, and FIG. 7 is a characteristic curve diagram showing a relationship between frequency (period) and delay time. The description of the same operation as that of the embodiment shown in FIG. 1 is omitted.

As shown in FIGS. 6 (a), 6 (c), 6 (d) and 6 (e), the position / delay correction circuit 14 is a phase measurement circuit 2a.
From the periodic signal 102, the time signal 104, the count signal 1
03 and the position information signal 105 are read. The cycle of the reference signal shown in FIG. 6B is set in advance. Further, the processes shown in (a) to (g) are the same as those in the flowchart shown in FIG.

As shown in FIG. 6 (k), the position / delay correction circuit 14 calculates the delay correction time “t2” from the latest measured cycle “T”. A reference table is created in advance based on a characteristic curve diagram showing the relationship between frequency (period) and delay time shown in FIG. 7, and the position / delay correction circuit 14 uses the latest period “T” measured using this reference table. To obtain the delay time “τ”. Then, a difference between the reference period and the delay time is obtained.

For example, if the latest measured cycle “T” is “
In the case of “T1”, the delay time “τ1” is “6n” from FIG.
On the other hand, since the delay time “τ0” of the reference period “T0” is “4 ns” from FIG. 7, the delay correction time “t2” is t2 = 6 ns−4 ns = 2 ns (6) Become.

Also, for example, the latest measured cycle “
When T "is" T2 ", the delay time" τ2 "is obtained from FIG.
Becomes "3 ns". On the other hand, since the delay time “τ0” of the reference period “T0” is “4 ns” from FIG. 7, the delay correction time “t2” is t2 = 3 ns−4 ns = −1 ns (7)

Then, as shown in FIG. 6 (l), the position / delay regulation circuit 14 calculates the elapsed time “t1” after the period measurement from FIG. 6 (g) as the delay correction time “t2” as shown below. to correct. t1 = t + (Tref × Sc) + t2 (8)

Next, as shown in FIG. 6 (h), the position / delay correction circuit 14 calculates the ratio of the elapsed time after the cycle measurement to the latest measured cycle, {t + (Tref × Sc) + t2} / T (9)

Further, as shown in FIG. 6 (i), the position / delay correction circuit 14 calculates the estimated moving distance “d1” after period measurement from the equations (1) and (9), and d1 = (T−Tref) × {t + (Tref × Sc) + t2} / T (10)

Finally, as shown in FIG. 6 (j), the position / delay correction circuit 14 adds the estimated moving distance after period measurement obtained by the equation (10) to the position information read in FIG. 6 (e). The position information is corrected and output as a corrected position information signal 107.

As a result, the period of the interference signal and the reference signal,
The position information can be corrected at the time of reading the position information by obtaining the estimated moving distance after the period measurement based on the count value and the time from the period measurement to the first read timing and correcting the circuit delay due to the input frequency. become.

For simplicity of explanation, the phase measuring circuit 2
Although a is provided with the function of sequentially integrating the phase differences, the position correction circuit 3 may of course have an integrating function.

It is also possible to use an arithmetic control circuit having both functions of the phase measuring circuit 2a and the position correcting circuit 3.

In the case where the position / delay correction circuit 14 calculates the delay correction time "t2", the reference table is used. However, the correction may be performed by approximating a straight line. For example,
If a straight line such as “SL01” shown in FIG. 7 is used and the slope is “K”, the delay correction time can be obtained as t2 = (T−T0) × K (11). By using such an approximate expression, it is possible to save the capacity of the storage circuit constituting the position / delay correction circuit 14.

It is also possible to use an arithmetic control circuit having both functions of the phase measurement circuit 2a and the position / delay correction circuit 14.

[0078]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. The position information can be corrected at the time of reading the position information by obtaining the estimated moving distance after the period measurement based on the period of the interference signal and the reference signal, the count value, and the time from the period after the period measurement to the first readout timing. A laser length measuring device can be realized.

Further, based on the period of the interference signal and the reference signal, the count value, and the time from the period after the period measurement to the first readout timing, the estimated moving distance after the period measurement is obtained, and the delay is corrected by the input frequency, thereby obtaining the position. The position information can be corrected at the time of reading the information.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a laser length measuring apparatus according to the present invention.

FIG. 2 is a timing chart showing a relationship between an interference signal, a reference signal, and a time from a period measurement to a first read timing.

FIG. 3 is a flowchart illustrating a calculation method of position correction.

FIG. 4 is a configuration block diagram illustrating details of a receiver and a position measurement circuit.

FIG. 5 is a block diagram showing a configuration of an embodiment of a laser length measuring apparatus according to the present invention, which takes into account correction of a circuit delay time.

FIG. 6 is a flowchart showing a calculation method of position correction and delay correction.

FIG. 7 is a characteristic curve diagram showing a relationship between frequency (period) and delay time.

FIG. 8 is a configuration block diagram showing an example of a conventional laser length measuring device.

FIG. 9 is a timing chart showing an example of a cycle measurement operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Receiver 2, 2a Phase measurement circuit 3 Position correction circuit 4 Photodetector 5, 8 Amplifier 6, 9 Filter circuit 7, 10 Comparator 11 PLL circuit 12 Period measurement circuit 13 Counter circuit 14 Position / delay correction circuit 100 Interference light 101 Reference signal 102 Period signal 103 Count signal 104 Time signal 105 Position information signal 106, 107 Corrected position information signal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Motobashi 2-9-132 Nakamachi, Musashino City, Tokyo Inside Yokogawa Electric Corporation (72) Inventor Yasuhito Kosugi 2-9-132 Nakamachi, Musashino City, Tokyo Next to Inside Kawa Electric Co., Ltd. (72) Inventor Nobuhiro Tomozada 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Co., Ltd. (72) Akira Oya 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Inside Electric Co., Ltd. (72) Inventor Hideto Iwaoka 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric

Claims (12)

[Claims] 1. A laser length measuring apparatus using heterodyne interference, comprising: a receiver for receiving an interference light and outputting an interference signal; a reference signal obtained by converting a difference between two frequencies into a voltage signal; A position measurement circuit that measures position information based on the position measurement circuit, and a position correction circuit that corrects the position information at the time of reading the position information by obtaining and adding an estimated movement distance after period measurement based on the output of the position measurement circuit. Laser measuring device characterized by comprising: 2. The method according to claim 1, wherein the position measurement circuit measures the period of the interference signal based on the reference signal to obtain the position information and measures a time from the period measurement to the first read timing. The laser length measuring device according to claim 1. 3. The laser length measuring apparatus according to claim 2, wherein the period of the interference signal is measured based on the reference signal. 4. The method according to claim 1, wherein the position correction circuit calculates the estimated moving distance after the period measurement based on the period of the interference signal and the reference signal and the time from the period after the period measurement to the first readout timing. The laser length measuring device according to claim 2. 5. The position correction circuit calculates the estimated moving distance after period measurement based on the period of the interference signal and the reference signal, the count value, and the time from the period measurement to the first readout timing. The laser length measuring apparatus according to claim 3, wherein: 6. A laser length measuring apparatus according to claim 1, further comprising an arithmetic control circuit having a function of said position measuring circuit and a function of said position correcting circuit. 7. A laser length measuring apparatus using heterodyne interference, comprising: a receiver for receiving an interference light and outputting an interference signal; a reference signal obtained by converting a frequency difference between two frequencies into a voltage signal; A position measurement circuit for measuring position information based on the position measurement circuit; and calculating and adding an estimated movement distance after period measurement in which a circuit delay due to an input frequency is corrected based on an output of the position measurement circuit, and adding the positions. And a position correction circuit for correcting information. 8. The position measuring circuit determines the position information by measuring the period of the interference signal based on the reference signal, and measures the time from the period measurement to the first readout timing. The laser measuring device according to claim 7. 9. The laser length measuring apparatus according to claim 8, wherein the period of the interference signal is counted based on the reference signal. 10. The position / delay correction circuit corrects the circuit delay of the time from the period measurement to the first readout timing, and the period of the interference signal and the reference signal and the period after the delay-corrected period is measured first. 9. The laser length measuring apparatus according to claim 8, wherein the estimated moving distance after period measurement is obtained based on the time until the read timing. 11. The position / delay correction circuit corrects the circuit delay of the time from the period measurement to the first read timing, and corrects the period of the interference signal and the reference signal, the count value, and the delay. 10. The laser measuring apparatus according to claim 9, wherein the estimated moving distance after the period measurement is obtained based on the time from the period measurement to the first read timing. 12. A laser length measuring apparatus according to claim 7, further comprising an arithmetic control circuit having a function of said position measuring circuit and a function of said position / delay correcting circuit.