JP6134169B2 - Signal analyzer - Google Patents

Description

  The present invention relates to a signal analysis device, and more particularly to analysis of serial communication.

  In the process control system, a differential pressure transmitter installed at the plant site, a transmitter such as a flow meter, a field device including an operation end such as a control valve, and a host system installed in the control room are connected via a digital line. Some are configured to exchange various information such as setting data and measurement data by connecting and performing serial communication between the field device and the host system.

  One type of serial communication is HART (Highway Addressable Remote Transducer) communication. HART communication is a communication method in which a digital signal is superimposed on an analog signal (for example, DC current 4 to 20 mA). The HART protocol defined by the HART Association is used, and the measured value of the detector, measured temperature value, and serial number are used for the digital signal. Such as device information. As a modulation method of HART communication, for example, continuous phase frequency-shift keying (hereinafter referred to as CPFSK) is used.

  By the way, in the maintenance inspection of the serial communication function of these field devices installed at the plant site, for example, a protocol analyzer or similar device is used to analyze communication data.

  As another method, as shown in FIG. 6, a digital oscilloscope 1 having a serial communication analysis function is also used. A CPFSK demodulator 2 is provided at the front stage of the digital oscilloscope 1. The digital oscilloscope 1 receives the CPFSK signal input to the CPFSK demodulator 2 and the output signal demodulated by the CPFSK demodulator 2. The digital oscilloscope 1 transmits the demodulated binary digital signal to the communication data. Analyze as

  Patent Document 1 describes a configuration of a communication line monitor device that can change a logic circuit for detecting a communication signal by a program according to a communication protocol.

JP 2008-90582 A

  However, according to the former method, a signal to be analyzed by a protocol analyzer or similar device is communication data in which a digital signal that is binarized is superimposed on an analog signal. It is not observable until it is in such a state.

  In addition, according to the latter method, in order to demodulate and analyze a binarized digital signal, an operator must operate buttons and switches provided on the operation panel of the digital oscilloscope 1. However, it takes a considerable amount of work.

  In the latter case, the digital oscilloscope 1 consumes two input channels because the CPFSK signal input to the CPFSK demodulator 2 and the output signal demodulated by the CPFSK demodulator 2 are input. It will be done, and handling is also bad.

  The present invention solves such a problem, and its purpose is to input only a CPFSK signal in which a binarized digital signal is superimposed on an analog signal, thereby demodulating the binary signal demodulated with the CPFSK signal. An object of the present invention is to provide a signal analysis apparatus that can also observe a digitized signal.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In a signal analyzer for measuring an output signal of a demodulated CPFSK signal,
Edge detection means for detecting the edge of the CPFSK signal that is input by being binarized and superposed on the two-frequency excitation signal by the measurement data of the electromagnetic flowmeter excited by the two-frequency excitation method ;
Transition point detecting means for detecting a transition point of the binarized signal based on the detected edge;
Binary signal demodulating means for demodulating the binary signal based on the detected transition point;
It is provided with.

The invention according to claim 2 is the signal analysis apparatus according to claim 1,
The signal analyzer also displays an input CPFSK signal.

The invention according to claim 3 is the signal analysis apparatus according to claim 1 or 2,
The signal analyzer is a digital oscilloscope.

The invention according to claim 4 is the signal analysis apparatus according to any one of claims 1 to 3,
The CPFSK signal is based on the HART protocol.

As a result, the output signal of the demodulated CPFSK signal can be observed with a relatively simple operation.
In addition, since errors do not accumulate at the time of demodulation, even a long continuous signal waveform can be demodulated correctly.

It is a block diagram which shows one Example of this invention. 2 is a timing chart illustrating the operation of FIG. 1. 3 is a flowchart illustrating a flow of demodulation processing of the CPFSK signal of FIG. 2. It is a flowchart which shows the example of application to field apparatus communication (HART). It is explanatory drawing of the high precision of CPFSK demodulation. It is a block diagram which shows the structural example of the conventional serial communication analysis function.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, showing an example of a digital oscilloscope. In FIG. 1, a CPFSK signal used as a communication signal for a field device, for example, a CPFSK signal obtained by binarizing measurement data of an electromagnetic flowmeter excited by a two-frequency excitation method and superimposing it on a two-frequency excitation signal is an amplifier 11. Is input to the A / D converter 12 via the signal, converted into a digital signal, and stored in a predetermined area of the memory 13.

  The edge detector 14 detects an edge of the CPFSK signal stored in the memory 13 according to a predetermined threshold set for edge detection. In this embodiment, an edge detection function of a digital oscilloscope is used as the edge detector 14.

  The CPU 15 obtains a high frequency component and a low frequency component of the two-frequency excitation constituting the CPFSK signal based on a predetermined program stored in the memory 13 and a detected edge detected by the edge detector 14, and corresponds to each of them. The value of the binarized signal is calculated. These calculation results are displayed on the display unit 16.

  The A / D converter 12, the memory 13, the edge detector 14, the CPU 15, and the display unit 16 are commonly connected by a bus 17 and constitute a digital oscilloscope 10.

FIG. 2 is a timing chart for explaining the operation of FIG. In FIG. 2, (a) is a threshold value, and is set to a predetermined value in accordance with the application in order to detect the edge of the CPFSK signal shown in (b). In the present embodiment, the time between the edges is obtained (t _{1 to} t ₇ ), and the regions divided by the edges are (A) to (I).

  Thereafter, binarization is performed in the process from path 1 to path 3 through path 2 shown in FIG.

<Path 1> Area where time between edges coincides with T _H , T _L Here, t ₁ = T _L , t ₃ = T _H , t ₆ = T _H , t ₇ = T _H , (B), (D), (G), (H) can be binarized.
The time of each region is, T _L, it is rare that exactly matches the T _H, may be a fact sufficiently close to the T _L, T _H is.

<Path 2> Area where time between edges is longer than T _{H and} less than T _L The ratio of the higher frequency side and the lower frequency side is obtained by the following equation.
t _L = T _L * (t−T _H ) / (T _L −T _H ) → the time of binarization H at the low frequency included in the region t _H = T _H * (T _L −t) / (T _L − T _H ) → High frequency included in region and binarized L time t: Time between edges Since the frequency is continuous with the adjacent region, the frequency of the target region transitions from high → low, low → high Decide what you did.

  Since the region (C) is continuous with the adjacent region (B) (frequency is low in pass 1, 2 is fixed as H), it can be determined that the frequency has changed from high to low, and the ratio is obtained from the above equation. Similarly, the areas (E) and (F) are also determined.

When the time of the region is close to T _L and T _H , there is a possibility that the transition is not caused by an error due to jitter. In this case, it should not be discontinuous with the adjacent region. For example, the region (C) is determined to have transitioned because (D) has a high frequency. If the region (D) has a low frequency, it is considered as jitter and no transition occurs.

<Path 3> Area where time between edges is T _L or more or areas at both ends ((A) and (I)
The start and end positions of the carrier are obtained from the positions of adjacent edges.
In the region (A), the carrier start t _b is obtained from t _a of the adjacent edge (region (C)) by the following equation.
t _b = (t _a / T _H ) * T _L
Similarly, the carrier stop t _d is obtained from t _c .
t _d = (t _c / T _L ) * T _H

  According to such a configuration, the CPFSK signal can be demodulated. In particular, by using the edge detection function of an existing digital oscilloscope, the most time-consuming edge detection can be performed at high speed, and no additional hardware is required, so that the cost is not increased.

  Less information is required for demodulation, and less information is specified by the user when it is incorporated into a device, so that a series of operations can be easily performed.

  That is, the high and low frequencies of the CPFSK signal are uniquely determined from the standard, and the threshold value for detecting the edge may be any voltage that intersects the signal waveform, and in many cases the trigger level.

  Further, since errors do not accumulate at the time of demodulation, even a long continuous signal waveform can be correctly demodulated.

  FIG. 3 is a flowchart for explaining the flow of demodulation processing of the CPFSK signal of FIG. First, an edge is detected and the time between the edges is obtained (step S1).

Next, a region where the time between edges is T _H is set to binarized L (step S2), a region where the time between edges is T _L is set to binarized H (step S3), and the time between edges is set to T _L The longer region is assumed to have no carrier (step S4).

Subsequently, the presence / absence of a region of T _H <inter-edge time <T _L is confirmed (step S5).
T _H <if there is a region of the edge between time <T _L is, T _H <calculates the ratio of H and L in the region of the edge interval period <T _L (step S6).

  Then, from the adjacent area, it is determined whether H → L or L → H (step S7). The transition between H and L in the region is determined from the ratio of H and L and the direction of change (step S8).

It is confirmed whether or not processing has been performed for all T _H <inter-edge time <T _L regions (step S9).

When the processing is completed for all the regions where T _H <inter-edge time <T _L , a change point of H / L adjacent to the section without carrier is searched (step S10).

  When there is a change point, the time of H / L existing in the area without carrier is obtained from the position of the change point (step S11).

In step S5, when there is no region of T _H <inter-edge time <T _L , the process proceeds to step S10.

If it is determined in step S9 that the processing has not been completed for all regions of T _H <inter-edge time <T _L , the process returns to step S6, and the processing steps after step S6 are repeated.

FIG. 4 is a flowchart showing an application example to field device communication (HART).
Specifically, the oscilloscope input setting is AC coupling, and a DC component of 4-20 mA is cut (step S1).

  CPFSK demodulation is performed with the frequency high (2200 Hz) set to 0 and the frequency low (1200 Hz) set to 1 (step S2), and the result is developed in the arithmetic memory of the oscilloscope.

  Then, UART analysis is applied to the arithmetic memory to perform HART communication analysis (step S3).

FIG. 5 is an explanatory diagram of increasing the accuracy of CPFSK demodulation.
(A) is a demodulation examples based on both edge detection, to measure the time t ₁ ~t _6. In this case, since the frequency transition point is included in the two regions, the position accuracy of the transition point is improved by performing statistical processing. Especially when there is a lot of jitter, the measurement accuracy can be increased.

(B) is an example of demodulation when edge detection is performed at two levels, and the times t _{1 to} t ₇ are measured. In this case, since the number of sample points increases, the measurement accuracy is improved.

  In the above embodiment, the example in which the signal analysis device is configured as a digital oscilloscope has been described. However, the present invention is not limited to this as long as it has the analysis function of the present invention. The analysis function of the invention may be incorporated.

  As described above, according to the present invention, by inputting only the CPFSK signal in which the binarized digital signal is superimposed on the analog signal, the signal analysis that can observe the CPFSK signal and the demodulated binarized signal as well. A device can be realized.

10 Digital Oscilloscope 11 Amplifier 12 A / D Converter 13 Memory 14 Edge Detector 15 CPU
16 Display 17 Bus

Claims (4)

In a signal analyzer for measuring an output signal of a demodulated CPFSK signal,
Edge detection means for detecting the edge of the CPFSK signal that is input by being binarized and superposed on the two-frequency excitation signal by the measurement data of the electromagnetic flowmeter excited by the two-frequency excitation method ;
Transition point detecting means for detecting a transition point of the binarized signal based on the detected edge;
Binary signal demodulating means for demodulating the binary signal based on the detected transition point;
A signal analysis apparatus comprising:   2. The signal analyzing apparatus according to claim 1, wherein the signal analyzing apparatus also displays an input CPFSK signal.   The signal analyzing apparatus according to claim 2, wherein the signal analyzing apparatus is a digital oscilloscope.   4. The signal analyzing apparatus according to claim 1, wherein the CPFSK signal is based on a HART protocol.

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