JP2006165737A - Analog signal processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an analog signal processing apparatus capable of executing temperature correction while avoiding the missing of measured data. <P>SOLUTION: The analog signal processing apparatus includes: an A-D conversion section for applying A-D conversion to an analog signal by each sampling period and outputting a digital value according to a prescribed offset and a prescribed gain; a reference voltage generating circuit for generating a reference voltage for temperature correction; a storage section for storing a first reference digital value being an output when the reference voltage is given to the A-D conversion section at a prescribed temperature; a temperature correction command section for commanding the execution of the temperature correction in each prescribed temperature correction period when the relation between the sampling unit time required for the processing of the A-D conversion section and the sampling period satisfies a prescribed relation; and a temperature correction execution section that gives a reference voltage to the A-D conversion section so as to correct an offset and a gain in a way that a second reference digital value being an output of the A-D conversion section is equal to the first reference digital value read from the storage section. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an analog signal processing device for a programmable logic controller that samples an analog signal input from a controlled object at a predetermined cycle. In detail, it is related with the improvement of the temperature correction function in an analog signal processor.

  In a programmable logic controller (hereinafter abbreviated as “PLC”), an analog signal input from a control target is sampled at a predetermined cycle, and A / D converted digital data is input to a CPU unit. An input unit is being used. Such a unit may have an analog output function to a control target as shown in Patent Document 1, for example, and is often called an analog signal processing unit or simply an analog unit. In this specification, an analog signal processing device or an analog input unit may be used.

  For example, a displacement meter is used to measure the distance or displacement to the measurement object (workpiece), and this corresponds to the control object of the PLC. An analog signal from the displacement meter is sampled by an analog signal processing device, and digital data after A / D conversion is input to the CPU unit. The CPU unit processes the digital data input from the analog signal processing device, and calculates a distance or displacement to the workpiece by performing a predetermined calculation.

  Since there is variation in the conversion characteristics of the A / D converter (analog signal to digital data converter) included in such an analog signal processing apparatus, the correction is performed. Normally, when there is no problem with linearity (linearity), offset and gain are corrected. For example, when the analog signal range is 0 to 10 V, the digital value corresponding to 0 V (lower limit value) and the digital value corresponding to 10 V (upper limit value) are measured and stored in the inspection / adjustment process at the time of shipment from the factory. The For convenience, the former is referred to as an offset correction value, and the latter is referred to as a gain correction value.

  Digital data obtained from the A / D converter in actual measurement is corrected using the offset correction value and the gain correction value, and digital data for each sampling period is sequentially output. For example, the distance to the measurement object is obtained by the arithmetic processing of these digital data. Patent Document 1 describes that the offset correction value and the gain correction value of the analog signal processing device are set by a command in a ladder language in the CPU unit.

  Moreover, since the A / D converter has a temperature characteristic in which the output varies depending on the ambient temperature, it is necessary to compensate for the temperature characteristic. That is, if the ambient temperature changes, even if the analog input voltage is the same, the digital data output from the A / D converter varies slightly, and it is difficult to perform precise measurement as it is. In order to compensate for temperature characteristics (hereinafter referred to as temperature correction), it is necessary to input a reference voltage (reference analog signal) to the A / D converter. For example, a reference voltage corresponding to the offset correction value and the gain correction value may be supplied to the A / D converter, and temperature correction may be performed so that the digital output matches the offset correction value and the gain correction.

In general, since the ambient temperature changes gradually, the above-described temperature correction is performed once every 30 seconds, for example. However, while A / D conversion of the reference voltage is being performed for temperature correction, A / D conversion for normal measurement cannot be performed, and measurement data during that time is lost. Depending on the application, errors due to missing data may be more problematic than errors due to temperature characteristics. Therefore, in the conventional analog signal processing apparatus, a switch for switching between enabling and disabling the temperature correction function is provided, and the temperature correction function is disabled when it is not desired to cause data loss. .
Japanese Patent Laid-Open No. 7-78007

  However, whether the temperature correction function is enabled or disabled as described above must be set by the user according to the application and the use environment, and if the setting is incorrect, there is a problem that the reliability of the measurement data is lowered.

  The present invention has been made in view of the problems as described above, and automatically determines the timing for executing temperature correction, and is an analog signal that achieves both avoidance of data loss and improvement of measurement accuracy by temperature compensation. An object is to provide a processing apparatus.

  A first configuration of an analog signal processing device according to the present invention is a sampling cycle setting for setting a sampling cycle of an analog signal input from a control target in an analog signal processing device connected to a CPU unit which is a main body of a programmable logic controller. A AD converter that A / D converts the analog signal for each sampling period and outputs a digital value according to a predetermined offset and gain, and a reference analog signal generator that generates a reference analog signal for temperature correction A storage unit that stores a digital value, which is an output of the AD conversion unit when the reference analog signal is input to the AD conversion unit at a predetermined ambient temperature, as a first reference digital value; and processing of the AD conversion unit Sampling unit time and the sampling period A temperature correction command unit that commands execution of temperature correction of the AD conversion unit every predetermined temperature correction cycle when the relationship satisfies a predetermined relationship, and the reference analog signal is converted into the AD according to the command of the temperature correction command unit Temperature correction execution that corrects at least one of the offset and the gain so that the second reference digital value that is input to the conversion unit is equal to the first reference digital value read from the storage unit. And a portion.

  In the analog signal processing apparatus having such a configuration, the temperature correction command unit automatically determines the conditions under which temperature correction can be performed while avoiding missing data, and commands the execution of temperature correction every temperature correction cycle. Therefore, it is not necessary for the user to set whether to enable or disable the temperature correction function. Therefore, there is no possibility that the reliability of the measurement data is deteriorated due to a setting error. The first reference digital value is stored in, for example, an inspection process at the time of factory shipment. This is a value corresponding to a predetermined offset and gain. On the other hand, the second reference digital value is a value obtained for temperature correction during actual measurement. Normally, two data are acquired for offset and gain temperature correction. However, if only one of the temperature corrections is sufficient, it is sufficient to acquire one data.

  According to a second configuration of the analog signal processing device of the present invention, as a specific configuration in the first configuration, the temperature correction command unit is configured to be predetermined if the set value of the sampling period is three times or more of the sampling unit time. The AD conversion unit is instructed to perform temperature correction at every temperature correction cycle, and the temperature correction execution unit performs the next sampling start timing after executing A / D conversion of the analog signal input from the control target The offset temperature correction data and the gain temperature correction data are continuously acquired by using the time until.

  According to such a configuration, it is possible to effectively use the remaining time when the digital value acquisition process corresponding to the analog signal input from the control target for measurement ends in a time of 1/3 or less of the sampling period. The offset temperature correction data and the gain temperature correction data can be acquired in succession. Therefore, temperature correction can be performed quickly while avoiding missing data acquired for measurement.

  According to a third configuration of the analog signal processing device of the present invention, in the first or second configuration, the temperature correction command unit is predetermined if the set value of the sampling period is twice or more the sampling unit time. The AD conversion unit is instructed to perform temperature correction at every temperature correction cycle, and the temperature correction execution unit performs the next sampling start timing after executing A / D conversion of the analog signal input from the control target One of the offset temperature correction data and the gain temperature correction data is acquired by using the time until.

  According to such a configuration, it is possible to effectively use the remaining time when the digital value acquisition process corresponding to the analog signal input from the control target for measurement ends in a time that is 1/2 or less of the sampling period. Either offset temperature correction data or gain temperature correction data can be acquired. When performing both offset and gain temperature corrections, offset temperature correction data and gain temperature correction data may be acquired in two sampling cycles. Therefore, even when a sampling period shorter than that of the second configuration is set, if the sampling period is twice or more the sampling unit time, temperature correction is performed while avoiding missing data acquired for measurement. be able to.

  According to a fourth configuration of the analog signal processing apparatus of the present invention, in the second or third configuration, a predetermined number of digital values obtained by A / D converting the analog signal input from the control target are sequentially provided. A data collection memory for storing, and when the set value of the sampling period is less than twice the sampling unit time, the temperature correction command unit has completed data collection for sequentially storing a predetermined number of the digital values The execution of temperature correction of the AD converter is instructed later.

  According to such a configuration, even when the relationship between the sampling unit time and the sampling cycle does not satisfy the predetermined relationship, that is, when a sampling cycle shorter than twice the sampling unit time is set, the predetermined number After completing the data collection, the temperature correction of the AD conversion unit can be executed. Generally, there is an upper limit to the number of digital values (predetermined number) stored in the data acquisition memory, and if the sampling period is shortened, the product of the predetermined number and the sampling period is small, so that it is shorter than a certain temperature correction period. There are many. Therefore, also in this case, temperature correction can be performed while avoiding missing data acquired for measurement.

  A fifth configuration of the analog signal processing device according to the present invention further includes a buffer memory to which a predetermined number of digital values stored in the data acquisition memory are transferred, and the CPU unit is configured to perform a predetermined control cycle or a user. The data stored in the buffer memory can be read in accordance with the command.

  According to such a configuration, the CPU unit can reliably pass a predetermined number of digital values that are sequentially sampled and stored to the CPU unit every predetermined control cycle or in accordance with a user's command, and the sampling cycle. Can be set to a smaller value.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a programmable logic controller (PLC) using an analog input unit which is an analog signal processing apparatus according to an embodiment of the present invention. As shown in FIG. 1, a CPU unit 1 and an analog input unit 2 are connected, and an analog signal from a control target is input to the analog input unit 2. As a control target, for example, various sensor devices such as a photoelectric sensor and a pressure sensor are connected, and an analog signal (voltage, current, etc.) that is an output signal thereof is input to the analog input unit 2.

  The analog input unit 2 includes an analog circuit 21, a processing unit 22, a data collection memory 23, and a slave ASIC 24. An analog signal input from the controlled object to the analog input unit 2 is A / D converted by the analog circuit 21 every predetermined sampling period, and its output (digital data) is given to the processing unit 22. The processing unit 22 performs an operation on the digital data and outputs a digital value for each sampling period. This calculation includes offset correction and gain correction of the A / D converter.

  The digital value for each sampling period output from the processing unit 22 is sequentially stored in the data collection memory 23. When a predetermined number of digital values are stored in the data acquisition memory 23, that is, when a time corresponding to the product of the sampling period and the predetermined number has elapsed, the processing unit 22 stores the predetermined value stored in the data acquisition memory 23. The digital value of the number is read and transferred to the buffer memory 241 built in the slave ASIC 24. The slave ASIC 24 is an ASIC (application-specific integrated circuit) on the analog input unit 2 side, and includes a communication interface 242 that controls the bus communication between the CPU unit 1 and the analog input unit 2 together with the buffer memory 241.

  The CPU unit 1 includes a master ASIC 11 and a control unit 12. The master ASIC 11 is an ASIC on the CPU unit 1 side, and includes a communication interface 111 and a memory 112 that control bus communication with the analog input unit 2. The control unit 12 executes various controls including communication control with the analog input unit 2 according to a sequence program described in a ladder language. Normally, bus communication with the analog input unit 2 is performed only once during the control cycle, and a predetermined number of digital values stored in the buffer memory 241 of the slave ASIC 24 of the analog input unit 2 are read. The read-out predetermined number of digital values are temporarily stored in the memory 112 in the master ASIC 11, read out as necessary, and used for various controls executed by the control unit 12.

  As a timing at which the CPU unit 1 performs bus communication with the analog input unit 2 and reads a digital value stored in the buffer memory 241, in accordance with a user command in addition to a periodic timing once in a control cycle. There is also a timing to read. The user can give a command to the CPU unit 1 by operating a program display using a touch panel, for example.

  FIG. 2 is a block diagram illustrating an internal configuration of an analog circuit and a processing unit in the analog input unit. Usually, a plurality of analog circuits 21 are connected to the processing unit 22 so that a plurality of analog signals can be input simultaneously (in parallel) from a plurality of controlled objects. In the illustrated example, a two-channel analog circuit 21 is connected to the processing unit 22. The plurality of analog circuits 21 are insulated from each other, and each analog circuit 21 incorporates a separate insulated power supply. Each analog circuit 21 and the processing unit 22 are connected by a photocoupler 25, and the output (digital signal) of the analog circuit 21 is passed to the processing unit 22 in a state where both are electrically insulated.

  The analog circuit 21 includes a reference voltage generation circuit (VREF) 211, a multiplexer (MPX) 212, an amplifier (AMP) 213, and an A / D converter (ADC) 214. The reference voltage generation circuit 211 corresponds to a reference analog signal generation unit that generates a reference voltage (reference analog signal) for variation correction and temperature correction of the A / D converter 214. The multiplexer 212 has a function of selectively switching between an analog signal input from the control target and a reference voltage from the reference voltage generation circuit 211. The analog voltage signal output from the multiplexer 212 is amplified by the amplifier 213, converted to a digital signal (data) by the A / D converter 214, and output from the analog circuit 21. This output is passed to the processing unit 22 via the photocoupler 25.

  The processing unit 22 includes a digital value calculation unit 221, a sampling cycle setting unit 222, a temperature correction execution unit 223, a temperature correction command unit 224, and a storage unit 225. For example, when the entire processing unit 22 is configured by a microcomputer, each of the above units is configured by microcomputer hardware and software. The digital value calculation unit 221 performs offset correction and gain correction on the digital data supplied from the A / D converter 214 of the analog circuit 21 and outputs a digital value for each sampling period. Therefore, the A / D converter 214 and the digital value calculation unit 221 correspond to an AD conversion unit that A / D converts an analog signal for each sampling period and outputs a digital value according to a predetermined offset and gain.

  The sampling cycle setting unit 222 sets the sampling cycle according to a command from the CPU unit 1. The sampling period is set to an appropriate time interval according to the application. In applications where the change in the analog signal from the control target (measurement target) is relatively slow, the sampling cycle can be set longer. Conversely, in an application where the analog signal from the control target changes abruptly, the sampling cycle can be set longer. It is necessary to set it short. However, it is not possible to set a sampling period shorter than the sampling unit time required for processing of the AD converter. The user can specify an appropriate sampling period using a user interface such as a computer connected to the CPU unit 1.

  Before describing the functions of the temperature correction execution unit 223, the temperature correction command unit 224, and the storage unit 225, offset correction and gain correction executed by the digital value calculation unit 221 will be briefly described with reference to FIG. FIG. 3 is a graph showing an example of A / D conversion characteristics when the analog input (voltage) V of the A / D converter 214 is taken on the horizontal axis and the digital output (data) D is taken on the vertical axis. A solid line represented by the formula D = αV represents an ideal A / D conversion characteristic, and a broken line represented by the formula D = d + βV represents the actual conversion characteristic of the A / D converter 214. . However, in reality, the conversion characteristic is not a straight line but stepwise, and the higher the resolution of the A / D converter 214 (the larger the number of bits), the finer the step. The correction that makes the intercept d on the Y axis on the straight line D = d + βV, which is an approximate conversion characteristic, zero corresponds to offset correction, and the correction that makes the slope β α (= D1 / 10) corresponds to gain correction. The intercept d and the slope β vary mainly due to variations in the A / D converter 214. However, it is assumed that linearity is compensated.

  Therefore, for example, in the inspection process at the time of factory shipment, the intercept d and the slope β (= (D2−d) /) from the digital outputs d and D2 when 0 V (lower limit value) and 10 V (upper limit value) are given as analog inputs. 10) can be obtained. These values are stored as an offset correction value and a gain correction value. Based on these correction values, the digital value calculation unit 221 executes dispersion correction (offset correction and gain correction) of the output of the A / D converter 214 obtained at the time of measurement.

  In the above example, 0 V (lower limit value) and 10 V (upper limit value) are generated by the reference voltage generation circuit 211 of each analog circuit 21 in FIG. Also, the input of the multiplexer 212 is switched to the reference voltage generation circuit 211 side, and the offset correction value and the gain correction value are acquired. The digital value calculation unit 221 (or storage unit 225) of the processing unit 22 stores the offset correction values and gain correction values of the plurality of analog circuits 21 for each channel. Note that a specific calculation method for offset correction and gain correction is not described, but the concept is the same as described with reference to FIG. Also, the stored offset correction value and gain correction value are not limited to the above examples, and various forms are conceivable.

  As described above, the acquisition and storage of the offset correction value and the gain correction value performed in the inspection process at the time of shipment from the factory are performed at a controlled predetermined temperature (for example, room temperature 25 ° C.). Since the output of the A / D converter 214 has a temperature characteristic that varies depending on the ambient temperature, it is necessary to compensate (temperature correction) for the output. That is, the first reference digital value obtained from the reference voltage at a predetermined temperature is stored in the storage unit 225, and the second reference digital value obtained from the reference voltage at every predetermined temperature correction period during measurement is the first reference value. Temperature correction is performed by correcting the offset correction value and the gain correction value so as to be equal to the digital value. The temperature correction is performed by the temperature correction execution unit 223, and the temperature correction command unit 224 instructs the temperature correction execution unit 223 to execute the temperature correction.

  The first reference digital value may be the offset correction value and the gain correction value for correcting the above-described variation. However, the temperature correction may be performed by correcting one of the offset correction value and the gain correction value. The storage unit 225 may be provided in the digital value calculation unit 221.

  The acquisition of the second reference digital value for temperature correction can be performed in the same manner as the acquisition of the offset correction value and the gain correction value (acquisition of the first reference digital value) performed in the inspection process at the time of shipment from the factory. . That is, the reference voltage is generated by the reference voltage generation circuit 211 and the input of the multiplexer 212 is switched to the reference voltage generation circuit 211 side. And when performing temperature correction of both an offset correction value and a gain correction value, what is necessary is just to perform correction | amendment according to the concept demonstrated with reference to FIG.

  As described above, at the timing when the input of the multiplexer 212 is switched to the reference voltage generation circuit 211 side to acquire the second reference digital value, the analog signal cannot be sampled from the controlled object. May be missing. However, in the analog input unit 2 of the present embodiment, the temperature correction command unit 224 determines the conditions under which the second reference digital value can be acquired without causing such missing measurement data, and the temperature correction command unit 224 The execution is commanded to the temperature correction execution unit 223. Several embodiments of the processing related to temperature correction of the processing unit 22 including the temperature correction command unit 224 and the temperature correction execution unit 223 will be described below.

  FIG. 4 is a diagram illustrating the temperature correction data acquisition timing according to the first embodiment. In this embodiment, the temperature correction command unit 224 determines the temperature every predetermined temperature correction period Tt (for example, 30 seconds) if the set value of the sampling period Ts is three times or more of the sampling unit time Ta (for example, 100 microseconds). Command execution of correction (acquisition of second reference digital value). The temperature correction execution unit 223 acquires normal measurement data (digital value corresponding to an analog signal from the control target) DATA1 in the first sampling unit time Ta, and then in the period P1 that is the second sampling unit time Ta. The offset temperature correction data is acquired, and the gain temperature correction data is acquired in the period P2, which is the third sampling unit time Ta. In this way, the offset temperature correction data and the gain temperature correction data, which are the second reference digital values, can be acquired without causing missing measurement data.

  FIG. 5 is a flowchart illustrating an example of processing performed by the processing unit 22 including the temperature correction execution unit 223 and the temperature correction command unit 224 according to the first embodiment. In step # 101, the process proceeds to step # 102 after the sampling unit time Ta has elapsed. Alternatively, the processing after step # 102 may be executed in accordance with an interrupt request generated every sampling unit time Ta. In step # 102, it is determined whether the sampling period Ts has elapsed. When the sampling period Ts has elapsed, normal measurement data is acquired in the next step # 103, and in the subsequent step # 104, offset correction and gain correction including temperature correction are executed, and a digital value for each sampling period is output. .

  If the sampling period Ts has not elapsed in step # 102, that is, if it is the second or subsequent sampling unit time Ta in the sampling period Ts, the process proceeds to step # 105 to check whether the temperature correction period Tt has elapsed. Is done. When the temperature correction cycle Tt has elapsed, it is checked in the next step # 106 whether or not it is the period P1 (second sampling unit time Ta). In the period P1, offset temperature correction data is acquired in the next step # 107. If it is not the period P1 in step # 106, it is checked in the next step # 108 whether or not it is the period P2 (third sampling unit time Ta). If it is the period P2, gain temperature correction data is acquired in the next step # 109. If it is not the period P2 in step # 108 (that is, a period after that), step # 109 is skipped. When the temperature correction cycle Tt has not elapsed in step # 105, the processing from step # 106 to step # 109 is skipped. Note that it is possible to determine whether it is the period P1 within the sampling period Ts, the period P2, or a period after that using a counter or a flag.

  Following the processing of step # 104, step # 107 or step # 109, it is checked in step # 110 whether a predetermined number of data collection has been completed. Steps # 101 to # 110 are repeated until a predetermined number of data collection is completed. As described with reference to FIG. 1, the predetermined number of digital values acquired for each sampling period are sequentially stored in the data acquisition memory 23, and then the predetermined number of digital values read from the data acquisition memory 23. The value is transferred to the buffer memory 241 of the slave ASIC 24.

  As described above, according to the present embodiment, the temperature correction command unit 224 determines the temperature correction data (second data) for each temperature correction cycle Tt if the set value of the sampling cycle Ts is three times or more the sampling unit time Ta. Command to obtain the reference digital value). In accordance with a command from the temperature correction command unit 224, the temperature correction execution unit 223 effectively uses the remaining time in the sampling period Ts after the end of normal data acquisition to obtain the offset temperature correction data and the gain temperature correction data. You can continue to get. Therefore, temperature correction can be performed quickly while avoiding missing measurement data.

  FIG. 6 is a diagram for explaining the acquisition timing of the temperature correction data according to the second embodiment. In this embodiment, the temperature correction command unit 224 executes temperature correction (acquisition of the second reference digital value) every predetermined temperature correction cycle Tt if the set value of the sampling cycle Ts is twice or more the sampling unit time Ta. ). The temperature correction execution unit 223 acquires normal measurement data (digital value corresponding to the analog signal from the control target) DATA1 in the first sampling unit time Ta, and offsets in the period Q1 which is the second sampling unit time Ta. Acquire temperature correction data. Then, in the next sampling period Ts, normal measurement data DATA2 is acquired in the first sampling unit time Ta, and gain temperature correction data is acquired in the period Q2 that is the second sampling unit time Ta. That is, the offset temperature correction data and the gain temperature correction data are acquired in two sampling cycles Ts.

  FIG. 7 is a flowchart illustrating an example of processing performed by the processing unit 22 including the temperature correction execution unit 223 and the temperature correction command unit 224 according to the second embodiment. The processing from step # 201 to step # 204 is the same as the processing from step # 101 to step # 104 in FIG. In step # 205, it is checked whether or not the temperature correction cycle Tt has passed. When the temperature correction cycle Tt has passed, it is checked in the next step # 206 whether or not it is the period Q1 (see FIG. 6). . When the period is Q1, offset temperature correction data is acquired at the next step # 207, and when it is not the period Q1 (after it), step # 207 is skipped.

  If the temperature correction cycle Tt has not elapsed in step # 205, it is checked in next step # 208 whether or not it is the period Q2 (see FIG. 6). If it is the period Q2, the gain temperature correction data is acquired in the next step # 209, and if it is not the period Q2 (after it), the step # 209 is skipped.

  Following the processing of step # 204, step # 207 or step # 209, it is checked in step # 210 whether a predetermined number of data collection has been completed. The processing from step # 210 to step # 210 is repeated until a predetermined number of data collection is completed. Similar to the first embodiment, a predetermined number of digital values are sequentially stored in the data collection memory 23 and then transferred to the buffer memory 241 of the slave ASIC 24.

  As described above, according to the present embodiment, the temperature correction command unit 224 determines that the temperature correction data (second data) is set for each temperature correction cycle Tt if the set value of the sampling cycle Ts is twice or more the sampling unit time Ta. Command to obtain the reference digital value). The temperature correction execution unit 223 effectively uses the remaining time within the sampling period Ts after the end of normal data acquisition in accordance with the command from the temperature correction command unit 224 to use the offset temperature correction data and the gain temperature correction data. Can be obtained by dividing into two sampling periods Ts. Therefore, temperature correction can be performed while avoiding missing measurement data.

  Note that when either one of the offset and gain temperature corrections is sufficient, the second reference digital value can be acquired in one sampling cycle Ts (period Q1 in FIG. 6). Further, this embodiment can be combined with the first embodiment. That is, if the set value of the sampling period Ts is three times or more of the sampling unit time Ta, the temperature correction command unit 224 instructs the acquisition of the second reference digital value based on the first embodiment and sets the set value of the sampling period Ts. If it is less than 3 times the sampling unit time Ta and 2 times or more, the acquisition of the second reference digital value may be instructed based on the second embodiment.

  FIG. 8 is a diagram for explaining the acquisition timing of the temperature correction data according to the third embodiment. In this embodiment, the temperature correction command unit 224 stores a predetermined number of measurement data (data collection) when the product n × Ts of the data collection number (predetermined number) n and the sampling period Ts is smaller than the temperature correction period Tt. ) Is executed, the execution of temperature correction (acquisition of the second reference digital value) is commanded. In accordance with a command from the temperature correction command unit 224, the temperature correction execution unit 223 performs offset temperature correction using periods R1 and R2, which are two sampling unit times Ta, following acquisition of a predetermined number n of measurement data. Data and gain temperature correction data are acquired. That is, temperature correction data (second reference digital value) is acquired before the next data collection is started.

  FIG. 9 is a flowchart illustrating an example of processing performed by the processing unit 22 including the temperature correction execution unit 223 and the temperature correction command unit 224 according to the third embodiment. The processing from step # 301 to step # 304 is the same as the processing from step # 101 to step # 104 in FIG. However, if the sampling period Ts has not elapsed in step # 302, nothing is done and the process returns to step # 301.

  In step # 305, it is checked whether a predetermined number of data collection has been completed. Steps # 301 to # 305 are repeated until a predetermined number of data collection is completed. When the predetermined number of data collection is completed, offset temperature correction data is acquired in the next step # 306, and gain temperature correction data is acquired in the subsequent step # 307. Similar to the first embodiment, a predetermined number of digital values are sequentially stored in the data collection memory 23 and then transferred to the buffer memory 241 of the slave ASIC 24.

  This embodiment is effective when a sampling period Ts shorter than twice the sampling unit time Ta is set. In this case, since the remaining time in the sampling period Ts after acquiring the measurement data is short, the temperature correction data cannot be acquired by the methods of the first and second embodiments. However, the number (predetermined number) n of digital values (measurement data) stored in the data collection memory 23 has an upper limit, and if the sampling period Ts is shortened, the product n × Ts of the predetermined number n and the sampling period Ts is Since it becomes smaller, it is often shorter than a certain temperature correction cycle Tt. For example, when n = 10000 and Ts = 200 microseconds, n × Ts = 20 seconds, which is shorter than the above-described 30 seconds of the temperature correction period Tt. In this case, following the acquisition of the predetermined number n of measurement data, it is possible to acquire the temperature correction data until the next data collection is started. Therefore, in this case as well, temperature correction can be performed without causing data loss.

  If the product n × Ts of the predetermined number n and the sampling period Ts is longer than the temperature correction period Tt, the next data collection is started after waiting for the completion of acquisition of the predetermined number n of measurement data. It is possible to acquire temperature correction data in the meantime. In short, when a sampling cycle Ts shorter than twice the sampling unit time Ta is set, the temperature correction is made until the next data collection is started after completion of acquisition of a predetermined number n of measurement data. You just have to get the data. Moreover, you may implement this Example 3 in combination with either or both of Example 1 and Example 2.

  FIG. 10 is a diagram for explaining the acquisition timing of the temperature correction data in the analog input unit according to the fourth embodiment of the present invention. In this embodiment, the present invention is applied to an analog input unit having no data collection function. In the case of an analog input unit that does not have a data acquisition function, A / D conversion (data acquisition) is performed at an interval equal to the sampling unit time Ta in the first embodiment, and the obtained digital value (measurement data) is buffered. Written to memory. In this case, the buffer memory stores only the latest measurement data. That is, new measurement data is updated every sampling unit time Ta.

  On the other hand, the CPU unit performs bus communication at an interval Tc longer than the sampling unit time Ta, and reads the latest measurement data stored in the buffer memory of the analog input unit. In the example of FIG. 10, the bus communication interval Tc is set to exactly three times the sampling unit time Ta. At this time, the measurement data acquired at the sampling unit time Ta immediately before the bus communication is performed and written in the buffer memory is read out to the CPU unit. Therefore, the temperature correction data can be acquired using the periods P1 and P2 corresponding to the two previous sampling unit times Ta. In this case, no data is lost when viewed from the CPU unit.

  In this embodiment, the offset temperature correction data and the gain temperature correction data can be obtained continuously using the periods P1 and P2. However, as in the second embodiment, the offset temperature correction data and the gain temperature correction data are obtained. Data may be acquired in two steps. In this case, if the bus communication interval Tc is at least twice the sampling unit time Ta, it is possible to acquire temperature correction data without data loss as seen from the CPU unit. Further, when either one of the offset and gain temperature corrections is sufficient, the temperature correction data can be acquired only in the period corresponding to one sampling unit time Ta.

  As mentioned above, although the Example and modification of this invention were demonstrated, this invention is not restricted to the structure shown to these Examples and modification, It can implement with a various form. For example, in the configuration of the first embodiment shown in the block diagram of FIG. 1, the data collection memory 23 and the buffer memory 241 are provided separately, and the buffer memory 241 is included in the slave ASIC 24. May be configured as different storage areas of a common storage device.

It is a block diagram which shows schematic structure of the programmable logic controller using the analog signal processing apparatus which concerns on the Example of this invention. It is a block diagram which shows the internal structure of the analog circuit in an analog input unit, and a process part. It is a graph for demonstrating offset correction and gain correction. It is a figure explaining the acquisition timing of the data for temperature correction which concerns on Example 1. FIG. 3 is a flowchart illustrating an example of processing by a processing unit according to the first embodiment. It is a figure explaining the acquisition timing of the data for temperature correction which concerns on Example 2. FIG. 10 is a flowchart illustrating an example of processing performed by a processing unit according to the second embodiment. It is a figure explaining the acquisition timing of the data for temperature correction which concerns on Example 3. FIG. 10 is a flowchart illustrating an example of processing performed by a processing unit according to the third embodiment. It is a figure explaining the acquisition timing of the data for temperature correction which concerns on Example 4. FIG.

Explanation of symbols

1 CPU unit 2 Analog input unit (analog signal processing device)
22 processing unit 23 data acquisition memory 211 reference voltage generation circuit (reference analog signal generation unit)
214 A / D converter (AD converter)
221 Digital value calculation unit (AD conversion unit)
222 Sampling cycle setting unit 223 Temperature correction execution unit 224 Temperature correction command unit 225 Storage unit 241 Buffer memory

Claims (5)

An analog signal processing device connected to a CPU unit which is a main body of a programmable logic controller,
A sampling period setting unit for setting the sampling period of the analog signal input from the control target;
An A / D converter for A / D converting the analog signal at each sampling period and outputting a digital value according to a predetermined offset and gain;
A reference analog signal generator for generating a reference analog signal for temperature correction;
A storage unit for storing, as a first reference digital value, a digital value that is an output of the AD conversion unit when the reference analog signal is input to the AD conversion unit at a predetermined ambient temperature;
A temperature correction command unit that commands execution of temperature correction of the AD conversion unit for each predetermined temperature correction period when a relationship between a sampling unit time required for processing of the AD conversion unit and the sampling period satisfies a predetermined relationship; ,
In accordance with a command from the temperature correction command unit, the reference analog signal is input to the AD conversion unit, and the second reference digital value output from the AD conversion unit becomes equal to the first reference digital value read from the storage unit. An analog signal processing apparatus comprising: a temperature correction execution unit that corrects at least one of the offset and the gain. If the set value of the sampling period is three times or more of the sampling unit time, the temperature correction command unit commands execution of temperature correction of the AD conversion unit for each predetermined temperature correction period, and the temperature correction execution unit Continuously uses the offset temperature correction data and the gain temperature correction data using the time until the next sampling start timing after executing A / D conversion of the analog signal input from the control target. The analog signal processing device according to claim 1, wherein the analog signal processing device is acquired. If the set value of the sampling period is twice or more the sampling unit time, the temperature correction command unit commands execution of temperature correction of the AD conversion unit every predetermined temperature correction period, and the temperature correction execution unit Is one of the offset temperature correction data and the gain temperature correction data using the time until the next sampling start timing after the A / D conversion of the analog signal input from the control target is executed. The analog signal processing device according to claim 1, wherein one of the signals is acquired. A data acquisition memory for sequentially storing a predetermined number of digital values obtained by A / D converting an analog signal input from the control target; and the temperature correction command unit is configured so that the set value of the sampling period is the sampling value The execution of temperature correction of the AD converter is instructed after completion of data collection for sequentially storing a predetermined number of the digital values when the time is less than twice the unit time. Analog signal processing device. A buffer memory to which a predetermined number of digital values stored in the data collection memory are transferred; and the CPU unit reads out the stored data of the buffer memory every predetermined control cycle or according to a user instruction The analog signal processing device according to claim 4, wherein the analog signal processing device is configured to be able to perform the processing.

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