Field instrument and diagnostic method

Abstract

According to the invention, the processing time required for fault diagnosis of the CPU carried by the field instrument is shortened. In a field device (10), a sensor (101) measures a predetermined physical quantity and outputs a sensor measurement value, which is a value indicating the measured physical quantity, and a first CPU (102) performs a predetermined operation and a predetermined fixed-cycle process on the sensor measurement value, and spontaneously transmits sequence information including the execution result of the fixed-cycle process. The second CPU (103) diagnoses whether or not the first CPU (102) has malfunctioned on the basis of a determination on the basis of the sequence information as to whether or not the fixed-cycle processing has been normally executed.

Description

Technical Field

[0001] The present invention relates to a field instrument and a diagnostic method. Background Art

[0002] Some field devices such as pressure gauges and flow meters have a configuration that includes a function for diagnosing a failure of a CPU (Central Processing Unit) mounted on the field device.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 08-234828 Summary of the Invention

[0004] It is preferred that the time required for CPU fault diagnosis be short.

[0005] Therefore, the present invention proposes a technique capable of shortening the processing time required for fault diagnosis of a CPU mounted on a field device.

[0006] A field device according to the present invention includes a sensor, a first CPU, and a second CPU. The sensor measures a predetermined physical quantity and outputs a sensor measurement value representing the measured physical quantity. The first CPU performs predetermined calculations and predetermined fixed-cycle processing on the sensor measurement value, and spontaneously transmits sequence information including the results of the fixed-cycle processing without receiving a request to obtain the sequence information. The second CPU determines whether the fixed-cycle processing has been executed normally based on the sequence information, thereby diagnosing whether the first CPU has a fault.

[0007] Effects of the Invention

[0008] According to the present invention, it is possible to shorten the processing time required for fault diagnosis of a CPU mounted on a field device. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a diagram showing a configuration example of a diagnostic system according to the first embodiment of the present invention.

[0010] Figure 2 This is a diagram showing an example of sequence information according to the first embodiment of the present invention.

[0011] Figure 3 This is a diagram showing an example of the operation of the first CPU according to the first embodiment of the present invention.

[0012] Figure 4 This is a diagram showing an example of the operation of the first CPU according to the first embodiment of the present invention.

[0013] Figure 5 This is a diagram showing an example of the operation of the first CPU according to the first embodiment of the present invention.

[0014] Figure 6 This is a diagram showing an example of the operation of the first CPU according to the first embodiment of the present invention.

[0015] Figure 7 This is a diagram showing an example of the operation of the second CPU according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0016] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. In the following embodiments, the same parts or processes may be denoted by the same reference numerals and repeated descriptions may be omitted.

[0017] [Example 1]

[0018] <Diagnostic system structure>

[0019] Figure 1 FIG. 1 is a diagram showing a configuration example of a diagnostic system according to Embodiment 1 of the present invention. Figure 1 In the present invention, diagnostic system 1 includes a field device 10, a host device 20, and a display 30. Examples of the field device 10 include a pressure gauge, a flow meter, a thermometer, and a level gauge. Examples of the host device 20 include a personal computer. Examples of the display 30 include an LCD (Liquid Crystal Display).

[0020] <Structure of field equipment>

[0021] exist Figure 1 In FIG. 1 , the field device 10 includes a sensor 101 , a first CPU 102 , a second CPU 103 , a third CPU 104 , a fourth CPU 105 , and an analog output device 106 . The field device 10 may also include a display 30 .

[0022] The sensor 101 measures a predetermined physical quantity and transmits a value indicating the measured physical quantity (hereinafter sometimes referred to as a “sensor measurement value”) to the first CPU 102 .

[0023] The first CPU 102 performs calibration, such as temperature correction, on the sensor's measured values, and performs predetermined calculations. The measured values ​​after calibration and predetermined calculations (hereinafter sometimes referred to as "calculated measured values") are transmitted to the second CPU 103. Furthermore, the first CPU 102 performs predetermined fixed-cycle processing and self-diagnosis of the first CPU 102, and transmits sequence information including the results of the fixed-cycle processing and the self-diagnosis to the second CPU 103. The first CPU 102 autonomously transmits the sequence information to the second CPU 103 at predetermined timings without receiving a request to obtain the sequence information from the second CPU 103.

[0024] The second CPU 103 transmits the digitally calculated measurement value to the third CPU 104. Furthermore, the second CPU 103 converts the digitally calculated measurement value into an analog current value and sets the converted current value (hereinafter sometimes referred to as the "analog measurement value") to the analog output device 106. Furthermore, the second CPU 103 does not transmit a request to the first CPU 102 to obtain sequence information.

[0025] In addition, the second CPU 103 performs fault diagnosis on the first CPU 102 by checking the sequence information sent from the first CPU 102. The second CPU 103 diagnoses whether the first CPU 102 has a fault by determining whether the fixed-cycle processing of the first CPU 102 has been performed normally (hereinafter sometimes referred to as the "fixed-cycle processing determination") and whether the self-diagnosis of the first CPU 102 has been performed normally (hereinafter sometimes referred to as the "self-diagnosis determination"). If the second CPU 103 detects an abnormality in both the fixed-cycle processing determination and the self-diagnosis determination, or in one of the fixed-cycle processing determination and the self-diagnosis determination, it diagnoses that the first CPU 102 has a fault. In addition, when the second CPU 103 diagnoses that the first CPU 102 has a fault, it sets the simulated current value to the current value output during burnout (hereinafter sometimes referred to as the "burnout value") and sets the current value set to the burnout value to the analog output device 106.

[0026] The third CPU 104 transmits the calculated measurement value to the fourth CPU 105 , and at the same time performs on-site communication with the host device 20 via the analog output device 106 .

[0027] The fourth CPU 105 causes the display 30 to display the calculated measurement value.

[0028] The analog output device 106 outputs the analog current value set by the second CPU 103 to the host device 20 .

[0029] The host device 20 supplies power to the field device 10 and conducts field communication with the third CPU 104 via the analog output device 106. If the current value set by the second CPU 103 is the exhaustion value, the host device 20 determines that an abnormality has occurred in either the fixed-cycle processing determination or the self-diagnosis determination, or in either the fixed-cycle processing determination or the self-diagnosis determination, and performs abnormality processing. As an abnormality processing, the host device 20 stops the operation of the field device 10 by, for example, stopping the power supply to the field device 10.

[0030] Sequence information

[0031] Figure 2 FIG. 1 is a diagram showing an example of sequence information according to the first embodiment of the present invention. Figure 2 The sequence information SI includes a sequence number SN, process numbers 1 to p of the fixed-cycle processes of the first CPU 102 , and diagnosis bits 1 to q of the self-diagnosis of the first CPU 102 .

[0032] exist Figure 2 In the figure, as an example, a case where the first to fifth fixed-cycle processes are performed by the first CPU 102 (i.e., a case where "p" is "5") is shown. Examples of the five fixed-cycle processes performed by the first CPU 102 include a measurement completion interrupt process (an interrupt process for receiving a notification from the sensor 101 indicating that measurement by the sensor 101 has been completed (hereinafter sometimes referred to as a "measurement completion notification"), a sensor measurement value reading process (a process for reading a sensor measurement value from the sensor 101), a calibration process for the sensor measurement value, a predetermined calculation process for the sensor measurement value, and a transmission process (a process for transmitting the calculated measurement value and sequence information to the second CPU 103).

[0033] In addition, Figure 2 In the figure, as an example, the case where the first to fourth four self-diagnostic processes are performed in the first CPU 102 (i.e., the case where "q" is "4") is shown. As the four self-diagnostic processes performed in the first CPU 102, for example, EDC (Error Detection Code) read diagnostic process, RAM (Random Access Memory) advance diagnostic process, CPU command test process, and MPU (Micro Processor Unit) diagnostic process can be cited. In the EDC read diagnostic process, the entire area of ​​the RAM that enables the EDC is read to confirm that no abnormal changes in the RAM are caused. In the RAM advance diagnostic process, the entire area of ​​the RAM is tested to confirm that no bit lock (Bit Lock) of the RAM is caused. In the CPU command test process, all commands of the first CPU 102 are tested and executed to confirm that there is no fault in the processing system of the first CPU 102. In the MPU diagnostic process, the memory protection based on the MPU is tested and executed to confirm that the MPU is performing the action normally.

[0034] The sequence number SN included in the sequence information SI is an identifier indicating the order in which each piece of sequence information SI is transmitted. It is used by the second CPU 103 to confirm that the sequence information SI is transmitted in order from the first CPU 102 to the second CPU 103. For example, the first CPU 102 increments the sequence number SN by "1" each time it generates sequence information SI. The second CPU 103 confirms that the sequence number SN is incremented by "1" each time it receives sequence information SI from the first CPU 102. If the sequence number SN does not increment by "1," the second CPU 103 diagnoses that the first CPU 102 has failed.

[0035] Furthermore, the increment of the sequence number SN is not limited to "1" and may be greater than or equal to "2." Furthermore, identifiers other than the sequence number SN may be used as identifiers indicating the order in which each sequence information SI is transmitted. For example, the first CPU 102 may change the identifier according to a predetermined pattern each time it generates sequence information SI. If the identifier change pattern included in the received sequence information SI does not match the predetermined pattern, the second CPU 103 may diagnose that the first CPU 102 has failed.

[0036] The processing numbers 1 to p of the fixed-cycle processing are data used to allow the second CPU 103 to confirm that p types of fixed-cycle processing, namely the first fixed-cycle processing to the p-th fixed-cycle processing, are executed in sequence in the first CPU 102. For the first fixed-cycle processing to the p-th fixed-cycle processing, unique processing numbers 1 to p are pre-assigned. Whenever the first CPU 102 executes each fixed-cycle processing, it records the processing number unique to each fixed-cycle processing in sequence in the sequence information SI. The second CPU 103 confirms that all processing numbers are recorded once in sequence (i.e., in the order of 1, 2, 3, ..., p) in the sequence information SI. When the execution of the fixed-cycle processing is normal, the processing numbers are arranged in the order of 1, 2, 3, ..., p. On the other hand, when the execution of the fixed-cycle processing is abnormal, for example, when the last fixed-cycle processing is not executed, the processing numbers are arranged in the order of 1, 2, 3, ..., p-1. Furthermore, for example, if a fixed-periodic process fails to execute correctly and the order of the second and third periodic processes is reversed, resulting in the third periodic process being executed before the second periodic process, the process numbers are arranged in the order of 1, 3, 2, ..., p. Furthermore, for example, if a fixed-periodic process fails to execute correctly and the second periodic process is executed twice, the process numbers are arranged in the order of 1, 2, 2, ..., p-1. If a fixed-periodic process fails to execute correctly, the second CPU 103 diagnoses that the first CPU 102 has failed.

[0037] The diagnostic bits 1 to q of the self-diagnosis are used by the second CPU 103 to confirm that q types of self-diagnostic processes, namely the first to qth diagnostic processes, have been started and completed one or more times within a constant time T3 in the first CPU 102. The diagnostic bits 1 to q correspond one-to-one to the first to qth diagnostic processes. The first CPU 102 sets the diagnostic bit to 0 at the time when the first to qth diagnostic processes are started, and sets the diagnostic bit to 1 at the time when the first to qth diagnostic processes are completed. The second CPU 103 holds the diagnostic bits 1 to q contained in the sequence information SI in an OR relationship with the hold variable V1, and holds the diagnostic bits 1 to q contained in the sequence information SI in an AND relationship with the hold variable V2. The initial value of the hold variable V1 is 0, and the initial value of the hold variable V2 is 1. After the constant time T3 has passed, the second CPU 103 confirms that all bits of the hold variable V1 are 1 and all bits of the hold variable V2 are 0. When the bit holding the variable V1 contains 0 and the bit holding the variable V2 contains 1, the second CPU 103 diagnoses that the first CPU 102 has failed.

[0038] Furthermore, to prevent erroneous diagnosis of a failure of the first CPU 102 when the sequence information SI is lost due to electrical noise or the like, the first CPU 102 may latch the state of the diagnosis bit so as to maintain the diagnosis bit at 0 over a plurality of cycles.

[0039] As described above, the second CPU 103 monitors the operation sequence of the first CPU 102 based on the sequence information SI.

[0040] <Operation of the First CPU>

[0041] Figure 3 、 Figure 4 、 Figure 5 and Figure 6 1 is a diagram showing an example of the operation of the first CPU according to the first embodiment of the present invention. Figure 3 As an example, the first diagnostic process is divided into three parts, namely diagnoses 1-1 to 1-3, the second diagnostic process is divided into five parts, namely diagnoses 2-1 to 2-5, the third diagnostic process is divided into two parts, namely diagnoses 3-1 and 3-2, and the fourth diagnostic process is divided into two parts, namely diagnoses 4-1 and 4-2. Figure 3 The fixed cycle processing shown includes five fixed cycle processings, namely the first fixed cycle processing to the fifth fixed cycle processing. Figure 3 In the example, the interval between time t1 and t2, the interval between time t3 and t4, and the interval between time t5 and t6 are equal to each other. Figure 3, the interval between time t2 and time t3 and the interval between time t4 and time t5 are equal to each other.

[0042] The first CPU 102 starts the first fixed cycle processing at time t1 when it receives the first measurement completion notification from the sensor 101. The first CPU 102 completes the first fixed cycle processing at time t2. Figure 4 The first sequence information SI-1 shown is sent to the second CPU 103, but is not stored. The first CPU 102 does not receive a sequence information acquisition request from the second CPU 103, but instead spontaneously sends the first sequence information SI-1 to the second CPU 103. At time t2, none of the first through fourth diagnostic processes are initiated, and therefore all diagnostic bits in the first sequence information SI-1 are set to 0.

[0043] Next, the first CPU 102 executes diagnoses 1 - 1 to 1 - 3 and diagnoses 2 - 1 to 2 - 4 during the period from time t2 to time t3 .

[0044] Next, the first CPU 102 starts the second fixed cycle processing at time t3 when it receives the second measurement completion notification from the sensor 101. The first CPU 102 sets the second fixed cycle processing to the time t4 when the second fixed cycle processing is completed. Figure 5 The second sequence information SI-2 shown is sent to the second CPU 103, but is not stored. The first CPU 102 does not receive a sequence information acquisition request from the second CPU 103, but instead spontaneously sends the second sequence information SI-2 to the second CPU 103. The first diagnostic process completes at time t4, so the diagnostic bit corresponding to the first diagnostic process in the second sequence information SI-2 is set to 1.

[0045] Next, the first CPU 102 executes interrupt processing, diagnosis 2-5, diagnosis 3-1, 3-2, diagnosis 4-1, 4-2, and diagnosis 1-1 during the period from time t4 to time t5. Figure 3 The interrupt processing shown is another interrupt processing that is not executed periodically, and an example thereof includes communication processing triggered by a setting change from the operating second CPU 103 .

[0046] Next, the first CPU 102 starts the third fixed cycle processing at time t5 when it receives the third measurement completion notification from the sensor 101. The first CPU 102 completes the third fixed cycle processing at time t6. Figure 6The third sequence information SI-3 shown is sent to the second CPU 103, but is not stored. The first CPU 102 does not receive a sequence information acquisition request from the second CPU 103, but instead spontaneously sends the third sequence information SI-3 to the second CPU 103. The second, third, and fourth diagnostic processes complete at time t6, so the diagnosis bits corresponding to the second, third, and fourth diagnostic processes are set to 1 in the third sequence information SI-3. Furthermore, the first diagnostic process begins anew at time t6, so the diagnosis bit corresponding to the first diagnostic process is set to 0 in the third sequence information SI-3.

[0047] After time t6, as described above, the first CPU 102 repeats the fixed cycle processing, the transmission of the sequence information SI, and the self-diagnosis processing.

[0048] Second CPU Operation

[0049] Figure 7 1 is a diagram showing an example of the operation of the second CPU according to the first embodiment of the present invention. Figure 7 In the process, the second CPU 103 confirms the diagnostic bits 1 to q in the sequence information SI received from the first CPU 102 after the constant time T3, thereby confirming in the first CPU 102 that the first diagnostic process to the qth diagnostic process have been started or equal to 1 times and completed within the constant time T3.

[0050] Constant time T3 is preset to satisfy the following conditions C1 and C2. If T1 is the time required for first CPU 102 to complete all diagnostic processes (i.e., the time required from the occurrence of an abnormality in first CPU 102 until second CPU 103 notifies first CPU 102 of the abnormality (i.e., the diagnostic response time of the device)), T4 is the period of the fixed-cycle processing performed by first CPU 102, T5 is the processing time of the fixed-cycle processing performed by first CPU 102, T6 is the time required for other interrupt processing performed by first CPU 102, and T1' is the time required for actual self-diagnosis other than the fixed-cycle processing and other interrupt processing, then conditions C1 and C2 for constant time T3 are expressed as follows.

[0051] Condition C1: T3 < T2

[0052] Condition C2: T1'<T3

[0053] Where, T1'=T1 / ((T4-T5-T6) / T4)+T4

[0054] Here, ((T4 - T5 - T6) / T4) represents the ratio of the time available for self-diagnosis during fixed-cycle processing, and T1 / ((T4 - T5 - T6) / T4) represents the actual time required for self-diagnosis. Since self-diagnosis processing has a lower priority than fixed-cycle processing and other interrupt processing, the actual self-diagnosis time is calculated by subtracting the fixed-cycle processing and other interrupt processing time from the total processing time of first CPU 102. Furthermore, +T4 represents a margin for timing variability.

[0055] The first embodiment has been described above.

[0056] [Example 2]

[0057] The second CPU 103 can diagnose a fault in the first CPU 102 only when it detects a plurality of M abnormalities in both the fixed-cycle processing determination and the self-diagnosis determination, or in one of the fixed-cycle processing determination or the self-diagnosis determination. This can prevent an erroneous diagnosis of a fault in the first CPU 102 when the sequence information SI is lost due to electrical noise or the like.

[0058] The number of times M is predetermined based on the relationship between time T1' and time T2. For example, when T1'=1 second and T2=5 seconds, the number of times M is preferably set to 2 or more and less than 5.

[0059] In addition, time T2 is the time required from the occurrence of an abnormality in the first CPU 102 until the second CPU 103 notifies the first CPU 102 of the abnormality, so the fault diagnosis of the first CPU must be completed within time T2. Therefore, it is preferred that the time required to perform N fault diagnoses of the first CPU be less than time T2.

[0060] The time T1 is determined according to the performance of the first CPU 102 and the second CPU 103, and the time T2 is determined according to the product specifications of the field device 10. Generally, the time T2 is preferably shorter.

[0061] The second embodiment has been described above.

[0062] [Example 3]

[0063] In Example 1, a single CPU is described as transmitting sequence information SI to the second CPU 103. However, the field device 10 may include multiple CPUs, each of which performs self-diagnostic processing and transmits sequence information SI to the second CPU 103. To prevent conflicts in sequence information SI, the multiple CPUs transmitting sequence information SI to the second CPU 103 are preferably connected to the second CPU 103 via separate communication lines.

[0064] The third embodiment has been described above.

[0065] As described above, the field device of the present invention (field device 10 of the embodiment) includes a sensor (sensor 101 of the embodiment), a first CPU (first CPU 102 of the embodiment), and a second CPU (second CPU 103 of the embodiment). The sensor measures a predetermined physical quantity and outputs a sensor measurement value representing the measured physical quantity. The first CPU performs predetermined calculations and predetermined fixed-cycle processing on the sensor measurement value, and autonomously transmits sequence information including the results of the fixed-cycle processing. The second CPU determines whether the fixed-cycle processing is executing normally based on the sequence information, thereby diagnosing whether the first CPU has a fault.

[0066] In this way, the second CPU performs fault diagnosis of the first CPU based on the sequence information spontaneously sent from the first CPU, so that the second CPU can perform fault diagnosis of the first CPU based on the sequence information received without an acquisition request for the first CPU, thereby shortening the processing time required for fault diagnosis of the first CPU.

[0067] In addition, several examples of combinations of the techniques of the present invention are described below.

[0068] (1) A field instrument, wherein:

[0069] The field device includes: a sensor that measures a predetermined physical quantity and outputs a sensor measurement value representing the measured physical quantity; a first CPU that performs a predetermined calculation and a predetermined fixed-cycle processing on the sensor measurement value and spontaneously transmits sequence information including the execution result of the fixed-cycle processing; and a second CPU that determines whether the fixed-cycle processing has been normally executed based on the sequence information, thereby diagnosing whether the first CPU has a fault.

[0070] (2) The field device according to (1), wherein:

[0071] The second CPU determines whether the fixed periodic process is executed normally by confirming whether the plurality of processes included in the fixed periodic process are executed in sequence, and diagnoses that the first CPU has a fault if the fixed periodic process is not executed normally.

[0072] (3) The field device according to (2), wherein:

[0073] When the second CPU fails to normally execute the fixed-cycle process a plurality of times, it is diagnosed that the first CPU has failed.

[0074] (4) The field device according to any one of (1) to (3), wherein:

[0075] The first CPU performs a self-diagnosis process on the first CPU, the sequence information includes an execution result of the self-diagnosis process, and the second CPU determines whether the self-diagnosis process is normally executed based on the sequence information, thereby diagnosing whether the first CPU has a fault.

[0076] (5) The field device according to (4), wherein:

[0077] The second CPU determines whether the self-diagnosis process is executed normally by confirming that the self-diagnosis process is started or completed once within a fixed time period, and diagnoses that the first CPU has a fault if the self-diagnosis process is not executed normally.

[0078] (6) The field device according to (5), wherein:

[0079] The second CPU diagnoses that the first CPU has failed when the self-diagnosis process is not performed normally a plurality of times.

[0080] (7) The field device according to (5), wherein:

[0081] The constant time is set based on the time required to complete the self-diagnostic processing in the first CPU, the time required from the occurrence of an abnormality in the first CPU until the second CPU notifies the abnormality, the cycle of the fixed cycle processing, and the processing time of the fixed cycle processing.

[0082] (8) The field device according to any one of (1) to (7), wherein:

[0083] The sequence information includes an identifier indicating a transmission order of the sequence information, and the second CPU diagnoses whether the first CPU has a fault by confirming the identifier.

[0084] (9) The field device according to (8), wherein:

[0085] The second CPU diagnoses that the first CPU has failed when the change pattern of the identifier does not match a prescribed pattern.

[0086] (10) The field device according to (9), wherein:

[0087] The second CPU diagnoses that the first CPU has failed when the identifier is not incremented by "1".

[0088] (11) The field device according to any one of (1) to (10), wherein:

[0089] When the second CPU diagnoses that the first CPU has failed, the second CPU sets an analog current value corresponding to the digital value obtained by the predetermined calculation in the first CPU as a drain value.

[0090] (12) The field device according to (3) or (6), wherein:

[0091] The number of times is predetermined based on the relationship between the time required for the first CPU to complete the self-diagnostic process and the time required from when an abnormality occurs in the first CPU until the second CPU notifies the abnormality.

[0092] (13) A diagnostic method for a field instrument comprising: a sensor for measuring a predetermined physical quantity and outputting a sensor measurement value representing the measured physical quantity; a first CPU; and a second CPU, wherein:

[0093] The first CPU performs prescribed calculations and prescribed fixed-cycle processing on the sensor measurement value, and spontaneously sends sequence information including the execution result of the fixed-cycle processing. The second CPU diagnoses whether the first CPU has a fault by determining whether the fixed-cycle processing has been performed normally based on the sequence information.

[0094] Description of the label

[0095] 10 Field Instruments

[0096] 101 Sensors

[0097] 102 First CPU

[0098] 103 Second CPU

Claims

1. A field instrument, wherein: The field instrument has: a sensor that measures a predetermined physical quantity and outputs a sensor measurement value representing the measured physical quantity; a first CPU that performs a predetermined calculation and a predetermined fixed-cycle process on the sensor measurement value, and spontaneously transmits sequence information including an execution result of the fixed-cycle process; and The second CPU determines whether the fixed cycle process is normally executed based on the sequence information, thereby diagnosing whether the first CPU has a fault.

2. The field instrument according to claim 1, wherein The second CPU determines whether the fixed periodic process is executed normally by confirming whether the plurality of processes included in the fixed periodic process are executed in sequence, and diagnoses that the first CPU has a fault if the fixed periodic process is not executed normally.

3. The field instrument according to claim 2, wherein: When the second CPU fails to normally execute the fixed-cycle process a plurality of times, it is diagnosed that the first CPU has failed.

4. The field instrument according to claim 1, wherein: The first CPU performs a self-diagnosis process on the first CPU, The sequence information includes the execution result of the self-diagnosis process, The second CPU determines whether the self-diagnosis process has been normally performed based on the sequence information, thereby diagnosing whether the first CPU has failed.

5. The field instrument according to claim 4, wherein: The second CPU determines whether the self-diagnosis process is executed normally by confirming that the self-diagnosis process is started or completed once within a fixed time period, and diagnoses that the first CPU has a fault if the self-diagnosis process is not executed normally.

6. The field instrument according to claim 5, wherein: The second CPU diagnoses that the first CPU has failed when the self-diagnosis process is not performed normally a plurality of times.

7. The field instrument according to claim 5, wherein: The constant time is set based on the time required to complete the self-diagnostic processing in the first CPU, the time required from the occurrence of an abnormality in the first CPU until the second CPU notifies the abnormality, the cycle of the fixed cycle processing, and the processing time of the fixed cycle processing.

8. The field instrument according to claim 1, wherein: The sequence information includes an identifier indicating the order in which the sequence information is sent. The second CPU diagnoses whether the first CPU has failed by confirming the identifier.

9. The field instrument according to claim 8, wherein: The second CPU diagnoses that the first CPU has failed when the change pattern of the identifier does not match a prescribed pattern.

10. The field instrument according to claim 9, wherein: The second CPU diagnoses that the first CPU has failed when the identifier is not incremented by "1".

11. The field instrument of claim 1, wherein: When the second CPU diagnoses that the first CPU has failed, the second CPU sets an analog current value corresponding to the digital value obtained by the predetermined calculation in the first CPU as a drain value.

12. A diagnostic method for a field device comprising: a sensor for measuring a predetermined physical quantity and outputting a sensor measurement value representing the measured physical quantity; a first CPU; and a second CPU, wherein: The first CPU performs a predetermined calculation and a predetermined fixed-cycle process on the sensor measurement value, and spontaneously transmits sequence information including the execution result of the fixed-cycle process. The second CPU determines whether the fixed cycle process is normally executed based on the sequence information, thereby diagnosing whether the first CPU has failed.

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