JP2014092395A - Temperature measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature measurement method that is able to measure a temperature highly accurately at low cost.SOLUTION: The voltage of an amplified thermocouple (3) is converted into a pulse of a predetermined frequency (F) by a V/F converter (6). The edge of the rise or fall of a pulse is counted for a measurement target time (GT), thereby obtaining the number (CNT) of pulses. By using a specific counter (9) counted up by a high speed clock and reset for each edge, a full pulse (FP) that is a counter value right before reset, start pulses (SP) that are counter values at the start and end of the measurement target time (GT), and an end pulse (EP) are obtained. A calculation is made using a frequency (F)={CNT+(EP-SP)/FP}/GT. A voltage is calculated from the frequency (F) and a temperature in a temperature sensor is calculated.

Description

  The present invention relates to a temperature measurement method for accurately measuring temperature using a thermocouple, and is not limited to temperature measurement suitable for measuring the temperature of a heating cylinder and injection nozzle of an injection molding machine. It is about the method.

  As is conventionally known, an injection molding machine includes an injection device that injects a molten resin into a pair of clamped molds. The injection device includes a heating cylinder and a screw that is driven in the rotation direction and the axial direction within the heating cylinder, and the heating cylinder is heated by being wound with a heater. The heating cylinder is embedded with multiple temperature sensors consisting of thermocouples, and the controller controls the heater ON / OFF based on the temperature measured by these temperature sensors, making it suitable for melting and injecting resin. The temperature is controlled.

  By the way, the controller is designed to perform digital processing. However, since a voltage as an analog electrical signal is detected by a temperature sensor composed of a thermocouple, the analog electrical signal is once obtained in order to obtain the temperature as a digital electrical signal. Must be amplified and converted into a digital signal voltage and subjected to computation to obtain the temperature. That is, at least an A / D converter is required. There are various types of A / D converters and there are advantages and disadvantages. However, if high accuracy is to be obtained, the cost increases. Even in the heating cylinder of the injection device, the accuracy required for temperature measurement is high, but an analog electric signal is converted into a digital electric signal by using an inexpensive and relatively high accuracy V / F converter.

  A method for obtaining temperature data by converting a voltage as an analog electric signal obtained from a thermocouple into a digital electric signal by a V / F converter and obtaining temperature data is described in various documents, for example, Patent Document 1. As is well known. Specifically, the processing is performed as shown in FIG. That is, the voltage detected in the thermocouple 51 is amplified by the amplifier 52 and converted into a pulse having a frequency proportional to the voltage by the V / F converter 53. The number of pulses is obtained by integrating the pulses in the counter 55, but the number of pulses is reset to 0 when a predetermined gate constituting the counter 55 is turned on based on a command from the gate control processing 56. And start integration. When the gate is turned off after a predetermined time has elapsed in the gate control process 56, the calculation process 58 reads the number of pulses from the counter 55 at that timing. That is, the number of pulses for the time when the gate is ON is obtained. This allows the pulse frequency to be calculated. The voltage detected by the thermocouple 51 depends on the relative temperature difference between the cold junction and the hot junction, and the frequency of the pulse output from the V / F converter 53 is proportional to the input voltage. Then, the voltage before amplification can be obtained and the temperature difference between the cold junction and the hot junction can be calculated therefrom. Since the absolute temperature of the cold junction is obtained by the resistance temperature detector 59, the temperature of the hot junction can be calculated.

JP-A-9-126904

  Even with the conventional method using the V / F converter 53, the temperature can be measured with relatively high accuracy by the temperature sensor including the thermocouple 51. Further, the V / F converter 53 is advantageous because of its low cost. However, there appears to be room for more accurate temperature measurement. The V / F converter 53 can convert the voltage into a pulse having a predetermined frequency, but the accuracy of this conversion is high. That is, there is almost no signal degradation in the conversion from voltage to frequency, and there is almost no decrease in resolution. However, the resolution is reduced in the process of obtaining this frequency. In other words, the frequency is calculated from the number of pulses integrated by the counter 55 and the ON time of the gate. However, since the number of pulses can only be obtained as an integer value, it is a jump value. That is, the decimal point is rounded up or rounded down, resulting in signal degradation. If it does so, the accuracy of the temperature measured by this amount will fall.

  An object of the present invention is to provide a temperature measurement method that solves the above-described problems. Specifically, the temperature can be measured with high accuracy in spite of the low cost, and is limited. Although not intended, it is an object of the present invention to provide a temperature measuring method suitable for application to a heating cylinder and an injection nozzle of an injection molding machine.

  In order to achieve the above object, the present invention converts a voltage of a thermocouple amplified as necessary into a pulse of a predetermined frequency (F) by a V / F converter. The number of pulses (CNT) is obtained by counting the measurement target time (GT) using the rising or falling edge of the pulse as the target edge. Using a predetermined counter that is counted up by a high-speed clock and reset at each target edge, a full pulse (FP) that is a counter value immediately before resetting and a start time and an end time of a measurement target time (GT) A start pulse (SP) and an end pulse (EP), which are counter values at, are obtained. Calculation is performed using frequency (F) = {CNT + (EP−SP) / FP} / GT. The voltage is calculated from the frequency (F), and the temperature at the temperature sensor is calculated.

Thus, in order to achieve the above object, the invention described in claim 1 amplifies the voltage detected in the temperature sensor composed of the thermocouple as necessary, and this is amplified by the V / F converter at a predetermined frequency ( F), the frequency (F) is sequentially calculated from the pulse, the voltage is sequentially calculated from the previous frequency (F), and the temperature at the temperature sensor is calculated. In the first counter, a first counter that counts a target edge with a falling edge as a target edge and a second counter that is counted up by a high-speed clock and reset for each target edge are used. Obtain a pulse number (CNT) that is the number of target edges for a predetermined measurement target time (GT), and in the second counter, A full pulse (FP) which is a counter value immediately before being reset by the target edge, a start pulse (SP) which is a counter value at the start and end of the measurement target time (GT), and an end pulse (EP And the frequency (F) of the pulse is
F = {CNT + (EP-SP) / FP} / GT
It is comprised as a temperature measuring method characterized by calculating by.
According to a second aspect of the present invention, in the method of the first aspect, the first counter is reset at the start of the measurement target time (GT), and the counter value at the end is set as the number of pulses (CNT). It is comprised as a temperature measuring method characterized by doing.
According to a third aspect of the present invention, in the method of the first or second aspect, the full pulse (FP) is obtained at a predetermined timing before the measurement target time (GT). Configured as
The method according to claim 4 is characterized in that, in an injection molding machine, the temperature of a heating cylinder and an injection nozzle in which a temperature sensor composed of a thermocouple is embedded is measured by the method according to any one of claims 1 to 3. Configured as a temperature measurement method.

  As described above, according to the present invention, the voltage detected in the temperature sensor composed of the thermocouple is amplified as necessary, and this is converted into a pulse of a predetermined frequency (F) by the V / F converter. It is configured as a temperature measurement method in which the frequency (F) from the pulse, the voltage from the frequency (F) are sequentially calculated, and the temperature in the temperature sensor is calculated. That is, since a V / F converter is used, the cost is small. The V / F converter converts the voltage into a pulse having a predetermined frequency. However, there is almost no deterioration in the conversion from the voltage to the frequency, and the conversion can be performed with high accuracy. According to the present invention, the first counter that counts the target edge with the rising edge or the falling edge of the pulse as the target edge, and the second counter that is counted up by the high-speed clock and reset for each target edge, Is used. The first counter obtains the number of pulses (CNT) that is the number of target edges of a predetermined measurement target time (GT), and the second counter is a full pulse (FP) that is a counter value immediately before being reset by the target edge. Then, a start pulse (SP) and an end pulse (EP), which are counter values at the start and end of the measurement target time (GT), are obtained, and the frequency (F) of the pulse is expressed as F = {CNT + ( EP-SP) / FP} / GT. Since the present invention is configured as described above, the frequency (F) can be calculated with high accuracy without error. Therefore, the temperature can be measured with high accuracy.

It is a block diagram which shows typically the temperature measuring device which concerns on embodiment of this invention. It is a graph which shows the pulse output from the V / F converter which comprises the temperature measurement apparatus which concerns on embodiment of this invention, and the change of the count value in each counter. It is a block diagram which shows the conventional temperature measuring apparatus typically.

  Hereinafter, this embodiment will be described. The temperature measurement method according to the present embodiment is configured as a method for measuring the temperature of a heating cylinder of an injection molding machine. The injection molding machine according to the present embodiment is also composed of an injection device that melts and injects resin, a mold clamping device that clamps a mold, and the like, similarly to a conventionally known injection molding machine. Is composed of a heating cylinder and a screw driven in the axial direction and the rotational direction in the heating cylinder. A plurality of heaters are wound around the heating cylinder and the injection nozzle provided at the tip thereof, and are heated by the heaters. One or more temperature sensors made of thermocouples are embedded in the heating cylinder and the injection nozzle. The temperature of the heating cylinder is measured by such a temperature sensor, but is accurately measured by the temperature measuring device 1 according to the present embodiment described below.

  As shown in FIG. 1, the temperature measuring apparatus 1 according to the present embodiment includes a temperature sensor 3 composed of a thermocouple, an amplifier 4 that amplifies the voltage of the temperature sensor 3, and an amplifier 4 that amplifies the voltage. A V / F converter 6 that outputs a voltage as an input, a first counter 8, that is, a pulse number counter 8, a second counter 9, that is, a pulse synchronization counter 9, a gate control process 10, and a high-speed clock 11 The calculation processing 12 and the temperature measuring resistor 14 for compensating for the cold junction of the temperature sensor 3 are configured. The pulse output from the V / F converter 6 is a rectangular wave as shown in FIG. 2, and the frequency F is proportional to the input voltage. The number of pulses is measured by counting such a rising edge or falling edge of the pulse by the pulse number counter 8. Any of these edges may be selected, but in the present embodiment, the falling edges 14, 14,... Are counted as the target edges 14, 14,. The pulse number counter 8 is composed of a flip-flop, a logic gate, etc., as in the known counter. Then, the number of target edges 14, 14,... Is integrated. When a predetermined gate is turned ON, the counter value is reset at the ON timing. The gate control process 10 is a process that is driven when the temperature is measured, and turns on / off the gate of the pulse number counter 8. In the present specification, since the gate time GT is also a time for measuring the number of pulses, it is expressed as a measurement target time GT. The gate control process 10 is performed based on an internal gate time counter (not shown) so that such a gate time GT becomes an exactly constant time. FIG. 2 shows how the counter values of the gate time counter of the gate control process 10 and the pulse number counter 8 change.

  As shown in FIG. 2, the pulse number CNT in the gate time GT, that is, the measurement target time GT is obtained by the pulse number counter 8, and the pulse frequency F is calculated from the measurement target time GT and the pulse number CNT. I can. However, the pulse number CNT can only be obtained as an integer. In other words, the fraction is rounded. More specifically, the target edge 14 a generated immediately after the start 15 of the measurement target time GT is counted up as one pulse in the pulse number counter 8. However, the time of a predetermined pulse width 19 has passed from the pulse start time 16 when the immediately preceding target edge 14b is generated to the pulse end time 17 when the target edge 14a is generated, and the measurement target time GT starts at the start time 15 The time from the end of the pulse to 17 is shorter than the pulse width 19. Then, the pulse counted up as one time includes an extra fraction of the pulse corresponding to the time from the pulse start time 16 to the measurement start time GT start time 15, that is, the time indicated by reference numeral 20. Will be. On the other hand, the target edge 14c generated immediately before the end of the measurement target time GT 21 is counted up in the pulse number counter 8, but the measurement target time GT ends from the pulse start time 22 when the target edge 14c occurs. The fraction of the pulse corresponding to the time up to hour 21, that is, the time indicated by reference numeral 24 is discarded. That is, the time indicated by reference numeral 24 includes the fraction of the next target edge 14d to be generated, but the fraction is not counted. Since the pulse number CNT obtained by the pulse number counter 8 is rounded in this way, the accuracy of the frequency F is not high when the frequency F is calculated from the pulse number CNT and the measurement target time GT.

  In the temperature measuring apparatus 1 according to the present embodiment, the frequency F can be calculated with high accuracy because the pulse synchronization counter 9 calculates the number of rounded fractions of the pulse number CNT. The pulse synchronization counter 9 operates as follows. That is, the pulse synchronization counter 9 is incremented by the clock from the high-speed clock 11 and is reset by the target edges 14, 14. Since the clock having a sufficiently high frequency is transmitted from the high-speed clock 11 as compared with the pulse output from the V / F converter 6, the counter value of the pulse synchronization counter 9 is shown in FIG. It changes like a saw.

  In such a pulse synchronous counter 9, a full pulse FP which is the maximum value of the counter value is obtained in advance. The full pulse FP is a counter value corresponding to the pulse widths 19 and 19 ′, but the value varies depending on the frequency of the pulse output from the V / F converter 6. However, it can be regarded as almost constant in a short time. The full pulse FP is obtained immediately before the measurement target time GT. The counter value at the start time 15 of the measurement target time GT is obtained by the pulse synchronization counter 9, and this is set as the start pulse SP. Further, the counter value at the end time 21 of the measurement target time GT is obtained by the pulse synchronization counter 9, and this is set as the end pulse EP.

The arithmetic processing 12 calculates the fraction of the pulse number CNT by these. First, in the pulse number CNT, an extra fraction is a fraction corresponding to the time indicated by reference numeral 20 and is given by SP / FP obtained by dividing the start pulse SP by the full pulse FP. The fraction discarded next is a fraction corresponding to the time indicated by reference numeral 24, and is given by EP / FP obtained by dividing the end pulse EP by the full pulse FP. Then, the number of pulses including the fraction, that is, the number of pulses CNT_R including the decimal point is given as follows.
CNT_R = CNT + (EP-SP) / FP
Since the frequency F of the pulse of the V / F converter 56 is obtained by dividing the number of pulses CNT_R including the decimal point by the measurement target time GT, it is given by the following equation.
F = CNT_R / GT
= {CNT + (EP-SP) / FP} / GT
That is, the arithmetic processing 12 calculates the frequency F by the above formula.

The arithmetic processing 19 includes the input voltage of the V / F converter 6 from the obtained frequency F, the amplifier 4
Calculate the voltage before amplification. The temperature measuring resistor 14 obtains the temperature of the cold junction of the thermocouple. These calculate the temperature at the hot junction of the thermocouple.

  The temperature measurement device according to the present embodiment can be variously modified. For example, the full pulse FP is obtained immediately before the measurement target time GT in the present embodiment. However, it can also be obtained at the measurement target time GT. You may obtain immediately after measurement object time GT. The pulse synchronization counter 9 can be modified. Although the pulse synchronization counter 9 has been described as being counted up by the external high-speed clock 11, it may be automatically counted up by providing a clock inside.

DESCRIPTION OF SYMBOLS 1 Temperature measuring device 3 Temperature sensor 4 Amplifier 6 V / F converter 8 Pulse number counter 9 Pulse synchronous counter 10 Gate control processing 11 High-speed clock 12 Arithmetic processing 14 RTD GT Measurement object time FP Full pulse SP Start pulse EP End pulse F Frequency CNT Number of pulses

Claims (4)

A voltage detected in a temperature sensor composed of a thermocouple is amplified as necessary, and converted into a pulse of a predetermined frequency (F) by a V / F converter, and the frequency (F) is converted from the pulse to the previous period. In a temperature measuring method for calculating the voltage sequentially from the frequency (F) and calculating the temperature in the temperature sensor,
Using a first counter that counts the target edge using a rising edge or a falling edge of a pulse as a target edge, and a second counter that is counted up by a high-speed clock and reset for each target edge;
In the first counter, a pulse number (CNT) that is the number of target edges of a predetermined measurement target time (GT) is obtained,
In the second counter, a full pulse (FP) which is a counter value immediately before being reset by the target edge, and a start pulse (SP) which is a counter value at the start and end of the measurement target time (GT). And end pulse (EP)
The frequency (F) of the pulse is
F = {CNT + (EP-SP) / FP} / GT
The temperature measurement method characterized by calculating by.   The method according to claim 1, wherein the first counter is reset at the start of the measurement target time (GT), and the counter value at the end is set to the pulse number (CNT). .   3. The temperature measuring method according to claim 1, wherein the full pulse (FP) is obtained at a predetermined timing before the measurement target time (GT). 4.   The temperature measuring method characterized by measuring the temperature of the heating cylinder and the injection nozzle in which the temperature sensor which consists of thermocouples was embedded in the injection molding machine by the method in any one of Claims 1-3.

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