JP2007309828A - Sectional type thermal type flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sectional type thermal type flow meter capable of securing compatibility between the sensor part and the display part for full measurement accuracy and at the sensor part also capable of informing the abnormality of the flowmeter, without having to select or to manufacture dedicated a heater-temperature detection resistor and a fluid-temperature detection resistor, and using general-purpose products. <P>SOLUTION: The sectional type thermal type flowmeter 10 comprises the memory 42 of the display part 40 for storing three kinds of data tables (a), (b) and (c) for covering the dispersion of the performance to be generated, when using the general-purpose products for the flow sensor 21 and the temperature sensor 22, and the table selection signal output part 24 for outputting the table selection signal, corresponding to the data tables (a), (b) and (c) to a sensor part 20. The abnormality information part 25 is provided in the sensor part 20, and the abnormality is notified by the LED 29. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thermal flow meter that measures a fluid flow rate based on an output from a constant temperature difference circuit including a heater temperature detection resistor (flow rate sensor) and a fluid temperature detection resistor (temperature sensor). More specifically, the present invention relates to a separation type thermal flow meter in which a sensor unit and a display unit are separated and a power supply voltage is supplied from the display unit to the sensor unit.

  Conventionally, a thermal flow meter has been used to measure the flow rate of compressed air and other fluids used in pneumatic lines and the like. The thermal flow meter includes a heater temperature detection resistor that is heated by a heater and a fluid temperature detection resistor that detects the temperature of the fluid to be measured. When the measurement fluid is not flowing, the heater temperature detection resistor is heated to a predetermined temperature by the heater, but when the measurement fluid flows, heat proportional to the mass of the fluid is lost. As a result, in order to return the heater temperature detection resistor to a predetermined temperature, a current flows through the heater temperature detection resistor (a voltage is applied). Based on the current value (voltage value), the flow rate of the fluid is calculated using a data table stored in advance (see Patent Document 1).

  Patent Document 1 discloses a thermal flow meter in which a sensor unit and a display unit are integrated. However, unlike this, the sensor unit and the display unit are separated and connected by a cable. Many type thermal flow meters are also used. In such a separation-type thermal flow meter, a signal relating to a current value (applied voltage value) that flows when the heater temperature detection resistor is returned to a predetermined temperature from the sensor unit is output to the display unit. In the display unit, the flow rate of the fluid is calculated by referring to a data table stored in advance in the display unit based on the signal.

JP-A-9-89618

  However, in the conventional separated type thermal flow meter described above, in order to ensure compatibility between the same model (to enable replacement of the sensor unit and the display unit between the same model), the heater temperature detection resistor It was necessary to reduce the individual difference (variation) of resistors such as platinum resistors or thermistors used as fluid temperature detection resistors. If the individual difference (variation) of the resistor is not reduced, the variation in the voltage output from the sensor unit according to the detected flow rate will increase, and the characteristics of the resistor in the sensor unit and the data table will not match well, making it accurate. In other words, the flow rate cannot be calculated (measured). In other words, measurement accuracy cannot be guaranteed. For this reason, in the conventional separation type thermal flow meter, resistors are selected or manufactured exclusively for reducing the individual difference (variation) of the resistors. There was a problem that became very expensive.

  In addition, in the conventional separation type thermal flow meter, the abnormality notification of the flow meter is generally performed in the display unit, but the flow meter is only to the extent that the presence or absence of energization is displayed in the sensor unit. There were no reports of any abnormalities. For this reason, when the sensor unit and the display unit are installed apart from each other, it is necessary to check the display unit for the presence or absence of an abnormality in the flow meter. was there.

  Therefore, the present invention has been made to solve the above-described problems, and a general-purpose product is used without selecting heater temperature detection resistors and fluid temperature detection resistors or specially manufactured, and a sensor unit and a display unit. It is an object of the present invention to provide a separation type thermal flow meter capable of ensuring compatibility and obtaining sufficient measurement accuracy. It is another object of the present invention to provide a separate thermal flow meter that can notify an abnormality in the flow meter even in the sensor unit.

  The thermal flow meter according to the present invention made to solve the above-described problems is a constant temperature including a body part in which a flow path is formed, a heater temperature detection resistor and a fluid temperature detection resistance installed in the flow path. A sensor unit that outputs a signal corresponding to the fluid flow rate by a difference circuit; and a display unit that calculates and displays a fluid flow rate based on an output signal from the sensor unit, the sensor unit and the display unit, In the separation type thermal flow meter in which the power supply voltage is supplied from the display unit to the sensor unit, the display unit has a data table that represents the relationship between the output signal from the sensor unit and the fluid flow rate. A plurality of memories, and the sensor unit includes a table selection signal output unit that outputs one of the table selection signals associated with each of the plurality of data tables to the display unit. When the table selection signal output from the sensor unit is input to the display unit, the display unit selects a data table corresponding to the table selection signal from the plurality of data tables and selects the data table. A separation type thermal flow meter that calculates a flow rate of a fluid based on a data table.

  In this separation type thermal flow meter, the flow rate of the fluid is calculated by referring to the stored data table on the display unit based on the signal corresponding to the flow rate of the fluid output from the sensor unit. Here, the display unit includes a memory that stores a plurality of data tables, and the sensor unit outputs a table selection signal that outputs one of the table selection signals associated with each of the plurality of data tables to the display unit. It has an output part. Then, the table selection signal output from the sensor unit is input to the display unit. Then, the display unit selects a data table corresponding to the table selection signal from a plurality of data tables stored in advance in the memory based on the input table selection signal, and uses the selected data table to select the fluid table. Is calculated.

  Therefore, even if there is an individual difference (variation) in the heater temperature detection resistance and fluid temperature detection resistance provided in the sensor unit, the display unit responds to the characteristics of the heater temperature detection resistance and fluid temperature detection resistance (considering the variation). Data table is selected, and the flow rate of the fluid is calculated using the selected data table. For this reason, even if there are individual differences (variations) in the heater temperature detection resistance and the fluid temperature detection resistance, the flow rate of the fluid can be measured with high accuracy.

  As a result, compatibility between the sensor unit and the display unit can be ensured without selecting the heater temperature detection resistor and the fluid temperature detection resistor, or without producing them exclusively. Thereby, even if a general-purpose product is used for the heater temperature detection resistor and the fluid temperature detection resistor, compatibility between the sensor unit and the display unit can be ensured, and sufficient measurement accuracy can be ensured. Further, if the number of data tables stored in the memory of the display unit is increased, the measurement accuracy can be improved. Furthermore, by increasing the memory capacity of the memory of the display unit and further increasing the number of data tables stored in the memory, compatibility between different types of models having different measurement flow ranges can be ensured.

  In the separation-type thermal flow meter according to the present invention, it is preferable that the table selection signal output unit includes a voltage setting unit that presets the table selection signal with a voltage value.

By doing so, for example, a table selection signal can be set every 0.1 V between 0 and 5 V, and a data table corresponding to the number of table selection signals set is stored in the memory of the display unit. The measurement accuracy of the flow rate can be easily adjusted.
Here, a variable resistor may be used as the voltage setting means. At this time, laser trimming processing or the like may be performed to prevent the resistance value from changing. A rotary switch may be used. With the rotary switch, the voltage (table selection signal) setting operation can be made very simple.

  In the separation-type thermal flow meter according to the present invention, the sensor unit may be configured such that when the voltage that changes according to the current flowing through the heater temperature detection resistor exceeds a preset reference voltage, the heater It is desirable to have an abnormality notification unit that determines that an abnormality has occurred in the temperature detection resistor and notifies the outside.

  Since the voltage increases or decreases in proportion to the current flowing through the heater temperature detection resistor, if a malfunction occurs due to foreign matter or water droplets adhering to the heater temperature detection resistor, a large current will flow through the constant temperature difference circuit (bridge circuit). Flowing. At this time, since the voltage that changes according to the current flowing through the heater temperature detection resistor exceeds a preset reference voltage, the abnormality notification unit notifies the outside of the heater temperature detection resistor. That is, notification of abnormality of the flow meter is also performed in the sensor unit.

  As a result, even when the sensor unit and the display unit are installed apart from each other, it is possible to check whether there is an abnormality in the flow meter in the sensor unit. Etc.) can be carried out quickly. Therefore, it is possible to reliably avoid a situation where the abnormality detection is delayed and the flowmeter is damaged.

  Note that the notification by the notification means can be made to emit a warning sound such as a buzzer in addition to a method of turning on or off a lamp (LED or the like) or blinking the lamp. Further, when the LED is turned on, two-color display (change of lighting color) may be performed. For example, it is only necessary to light green during normal times and light red when abnormal.

  In the separation type thermal flow meter according to the present invention, the sensor unit outputs a voltage value that changes according to a current flowing through the heater temperature detection resistor to the display unit, and the display unit When the value exceeds a preset upper limit value, it is desirable to stop supplying the power supply voltage to the sensor unit. The upper limit value may be set to a voltage value that may damage the constant temperature difference circuit (bridge circuit) provided in the sensor unit.

  By doing so, when there is a possibility that a large current flows through the circuit provided in the sensor unit and it is damaged, the supply of the power supply voltage to the sensor unit is forcibly stopped by the display unit. That is, the power supply of the sensor unit is automatically turned off. Accordingly, it is possible to reliably prevent the sensor portion from being damaged.

  In the separation type thermal flow meter according to the present invention, the sensor unit outputs the table selection signal to the display unit when the power is turned on, and the heater temperature detection resistor after a predetermined time has elapsed since the power was turned on. It is desirable to have a signal processing unit that outputs to the display unit a voltage value that changes according to the current flowing through the display.

  By having such a signal processing unit, it is possible to output two types of signals from one output port of the sensor unit to the display unit. That is, when a power supply voltage is supplied from the sensor unit to the display unit (when the power is turned on), a table selection signal is output, and after a certain period of time has elapsed, the current flowing through the heater temperature detection resistor The changing voltage value continues to be output. As a result, the display unit selects the data table corresponding to the sensor unit connected when the power is turned on, and thereafter monitors the abnormality of the voltage value that changes according to the current flowing through the heater temperature detection resistor.

  Therefore, when the combination of the sensor unit and the display unit is changed, an appropriate data table is automatically selected and the flow rate is calculated in the display unit. A measure for avoiding damage to the sensor unit is automatically performed. Therefore, a separation-type thermal flow rate that is very easy to handle is realized.

  According to the separation-type thermal flow meter of the present invention, as described above, a general-purpose product can be used without selecting the heater temperature detection resistor and the fluid temperature detection resistor, or using a dedicated product. Compatibility can be ensured and sufficient measurement accuracy can be obtained. Further, according to the separation type thermal flow meter according to the present invention, an abnormality in the flow meter can be notified also in the sensor unit.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a most preferred embodiment that embodies a separation type thermal flow meter of the present invention will be described in detail based on the drawings. Therefore, first, the configuration of the separation type flow meter according to the present embodiment will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of a separation-type thermal flow meter according to the embodiment. FIG. 2 is a circuit diagram illustrating a circuit configuration of the sensor unit. FIG. 3 is a block diagram illustrating a configuration of the display unit.

  As shown in FIG. 1, the separation-type thermal flow meter 10 according to the present embodiment includes a body 12 in which a flow channel 11 through which a measurement fluid flows is formed, and a sensor unit that detects the flow rate of the fluid flowing through the flow channel 11. 20, the display unit 40 that calculates and displays the flow rate of the fluid flowing through the flow path 11 based on the detection signal of the sensor unit 20, and the sensor unit 20 and the display unit 40 are electrically connected. Cable 16. The power supply voltage V + of the display unit 40 and the sensor unit 20 is supplied by the external power source Vcc connected to the display unit 40, and the flow rate value is displayed on the display unit 40 based on the flow rate signal detected by the sensor unit 20. It has become so.

  Here, pipe adapters 13 a and 13 b are attached to both ends of the body 12. Thereby, the sensor main body 15 can be attached to line piping. A flow rate sensor 21 that is a heater temperature detection resistor and a temperature sensor 22 that is a fluid temperature detection resistor are installed in the flow path 11 in the body 12. Further, the flow path 11 is provided with a rectifying unit 14 for adjusting the flow of the fluid flowing into the flow path 11 and removing foreign substances in the fluid.

  The sensor unit 20 is disposed on the upper portion of the body 12. The sensor unit 20 will be described with reference to FIG. As shown in FIG. 2, the sensor unit 20 includes a flow rate detection unit 23, a voltage setting unit 24, an abnormality notification unit 25, and a signal processing unit 26.

  The flow rate detector 23 detects the flow rate of the fluid flowing through the flow path 11, and outputs a detection signal (Q signal) to the display unit 40. The flow rate detector 23 includes a flow rate sensor 21 for detecting a flow rate, a temperature sensor 22 for fluid temperature compensation, a bridge circuit including fixed resistance elements R1, R2, and R3, an operational amplifier OP1, and a transistor Tr1. And. Here, the flow rate sensor 21 and the temperature sensor 22 are so-called temperature-sensitive resistance elements whose resistance values change depending on the temperature, such as platinum resistance and thermistor, and these resistance elements include a wire, a film, and a semiconductor type. There are various things. In the present embodiment, general-purpose platinum resistors are used as the flow rate sensor 21 and the temperature sensor 22. That is, the flow sensor 21 and the temperature sensor 22 are not selected or manufactured exclusively.

  The output of the flow sensor 21 is detected by the fixed resistance element R3 and input to the (+) terminal of the operational amplifier OP1. On the other hand, the output of the temperature sensor is detected by the fixed resistance element R2 and input to the (−) terminal of the operational amplifier OP1. The output of the operational amplifier OP1 is input to the base of the transistor Tr1. Thereby, in the flow rate detection unit 23, the current flowing through the flow rate sensor 21 is controlled so that the temperature difference (resistance value difference) between the flow rate sensor 21 and the temperature sensor 22 becomes constant. Here, since the flow sensor 21 is disposed in the flow path 11, heat is taken away by the fluid flowing through the flow path 11. At this time, the flow rate of the fluid flowing through the flow path 11 is detected by detecting it as a current value (voltage value) that varies depending on the flow rate of the fluid. The flow rate detection unit 23 finally outputs the q signal, and the Q signal amplified by the amplification circuit 27 is output from the sensor unit 20.

  The table selection signal output unit 24 outputs one of the table selection signals associated with each of a plurality of data tables stored in the memory 42 of the display unit 40 described later to the display unit 40. . The table selection signal output unit 24 includes a voltage setting unit 28 that presets the table selection signal with a voltage value. In the present embodiment, since three data tables (a), (b), and (c) are stored in the memory 42 of the display unit 40 as will be described later, voltage values of 1 V, 3 V, and 5 V are required to correspond to this. It is a rotary switch that can be set either.

  The voltage value is set so as to correspond to a data table suitable for each sensor body 15 (flow rate sensor 21 and temperature sensor 23). Specifically, when the output characteristics of the sensor unit 20 are compatible with the data table (a), “1V” is set as the table selection signal. Similarly, when the output characteristic of the sensor unit 20 matches the data table (b), “3V” is set as the table selection signal. Similarly, when the output characteristic of the sensor unit 20 matches the data table (c), “5V” is set as the table selection signal.

  The abnormality notification unit 25 detects an abnormality of the flow sensor 21 and the temperature sensor 22 and notifies the abnormality to the outside. The abnormality notification unit 25 includes an LED 29 for performing abnormality notification, and a comparison circuit OP2 to which a reference voltage for determining abnormality and a voltage (p signal) that changes according to the current flowing through the flow sensor 21 are input. I have. In normal times, the LED 29 is turned on by the power supply voltage V +, and when the p signal exceeds the reference voltage value, the LED 29 is turned off by the output signal from the comparison circuit OP2. Thereby, an abnormality can be detected by confirming the display of the LED 29 provided in the sensor unit 20. The reference voltage value may be set to about 3.5 to 3.8V, for example.

  The signal processing unit 26 outputs a table selection signal as a P signal output from the sensor unit 20 to the display unit 40 when the power is turned on, and thereafter changes a voltage (p signal) that changes according to the current flowing through the flow sensor 21. ) Is output. The signal processing unit 26 includes a delay circuit 30 and analog switches SW1 and SW2. The delay circuit 30 and the analog switch SW1 are directly connected, and the delay circuit 30 and the analog switch SW2 are connected via a NOT circuit 31. The power supply voltage V + is supplied to the delay circuit 30. Further, an output from the voltage setting unit 28 is input to the analog switch SW1, and a voltage (p signal) that changes according to the current flowing through the flow sensor 21 is input to the analog switch SW2. Thus, when the power is turned on, the analog switch SW1 is turned on and the analog switch SW2 is turned off, so that the table selection signal is output as the P signal. After that, when the time set by the delay circuit 30 (5 seconds in the present embodiment) elapses, the analog switch SW1 is turned off and the analog switch SW2 is turned on, so that the p signal is output as the P signal. It has become.

Next, the display unit 40 will be described with reference to FIG. As shown in FIG. 3, the display unit 40 includes a CPU 41, a memory 42, an A / D conversion unit 43, a setting switch 44, a display unit 45, and a transistor Tr2.
The CPU 41 calculates the flow rate of the fluid flowing through the flow path 12 based on the input signal (Q signal) from the sensor unit 20, and causes the display unit 45 to display the flow rate value according to the conditions set by the setting switch 44. It has become. Further, the CPU 41 operates the transistor Tr2 in response to an input signal (P signal) from the sensor unit 20 to stop the supply of the power supply voltage V + to the sensor unit 20.

  The memory 42 stores a plurality of data tables representing the relationship between the Q signal (output voltage) output from the sensor unit 20 and the fluid flow rate. This data table is referred to when the CPU 41 calculates the flow rate. In the present embodiment, three types of data tables (a) (b) (c) as shown in FIG. 4 are stored. FIG. 4 is a diagram showing the contents of the data table stored in the memory of the display unit. By storing about three types of data tables in the memory 42, even if general-purpose products are used as the flow rate sensor 21 and the temperature sensor 22 (without selecting or producing a dedicated product), either data table is used. It is designed to exhibit characteristics that meet the requirements. That is, the variation in output characteristics when general-purpose products are used as the flow sensor 21 and the temperature sensor 22 is within the variation width X shown in FIG.

  In addition, when the range of variation in output characteristics when using general-purpose products as flow rate sensors and temperature sensors is larger, when it is necessary to further improve the measurement accuracy, or compatibility between different types of sensor and display units When it is necessary to secure the data, the number of data tables stored in the memory 42 may be increased. In this case, it is necessary to increase the table selection signal (voltage value) set in the voltage setting unit 28 of the sensor unit 20 and to increase the storage capacity of the memory 42 in some cases.

  The memory 42 also stores an upper limit value of a voltage value (p signal) that changes according to the current flowing through the flow sensor 21. The upper limit voltage value may be set to such an extent that the circuit of the flow rate detection unit 23 of the sensor unit 20 is not damaged. In addition, as an upper limit, what is necessary is just to set to about 3.5-3.8V, for example.

  The A / D converter 43 converts signals (P signal and Q signal) from the sensor unit 20 into digital signals. The setting switch 44 is used for changing a measurement mode or a set value. The display unit 45 performs switch output display, abnormality display, unit display and the like in addition to digital display of the flow value.

Next, the operation of the separation type thermal flow meter 10 having the above-described configuration will be described. In the separated thermal flow meter 10, when the power is turned on, the power supply voltage V + is supplied from the external power supply Vcc to the display unit 40 and the sensor unit 20. Then, in the signal processing unit 26 of the sensor unit 20, the analog switch SW1 is turned on and the analog switch SW2 is turned off. For this reason, the voltage value (table selection signal) set by the voltage setting device 28 is output from the sensor unit 20 and input to the display unit 40 as a P signal. In the display unit 40 to which the table selection signal is input, the CPU 41 selects a data table corresponding to the input table selection signal. For example, when the table selection signal is “1V”, the data table (a) is selected from the memory 42 and read.
Further, the LED 29 is turned on. As a result, the fact that the sensor unit 20 is energized is displayed.

  The flow rate detection unit 23 of the sensor unit 20 controls the current flowing through the flow rate sensor 21 so that the temperature difference (resistance value difference) between the flow rate sensor 21 and the temperature sensor 22 is constant. Here, when a fluid flows through the flow path 11, heat is taken from the flow sensor 21. At this time, a current value (voltage value) that changes depending on the flow rate of the fluid is output as a q signal by the flow rate detection unit 23. The q signal is amplified by the amplifier circuit 27, output from the sensor unit 20 as a Q signal, and input to the display unit 40.

  Then, in the display unit 40, the CPU 41 refers to the data table read from the memory 42 based on the input Q signal (in the above example, the table (a)), and the flow path 11 is changed. Calculate the flow rate of the flowing fluid. Then, the CPU 41 displays the calculation result on the display unit 45 in accordance with the measurement mode set by the setting switch 44.

  Here, in the sensor unit 20, general-purpose platinum resistors are used as the flow rate sensor 21 and the temperature sensor 22, but when calculating the flow rate, a data table adapted to the characteristics of the flow rate sensor 21 and the temperature sensor 22. Is used. For this reason, even if it is the flow sensor 21 and the temperature sensor 22 which use a general purpose product, the flow volume of the fluid which flows through the flow path 11 can be measured accurately.

  As shown in FIG. 5, when the sensor body 15 is replaced with the sensor body 15a, a data table corresponding to the table selection signal output from the sensor unit 20a of the sensor body 15a is selected. FIG. 5 is an explanatory diagram illustrating a state in which different sensor bodies are connected to the same display unit. Here, general-purpose platinum resistors are also used for the flow rate sensor 21a and the temperature sensor 22a provided in the sensor unit 20a. Therefore, due to individual differences (variation) in platinum resistance of general-purpose products, the output characteristics of the Q signal are different between the sensor unit 20 including the flow sensor 21 and the temperature sensor 22 and the sensor unit 20a including the flow sensor 21a and the temperature sensor 22a. There is a risk of variation as shown in FIG.

  However, when the power is turned on after the sensor body 15a is replaced, a table selection signal is output as a P signal from the sensor unit 20a after the replacement and is input to the display unit 40. In the display unit 40, a data table corresponding to the input table selection signal is selected. For example, when the table selection signal output from the sensor unit 20a is “5V”, the data table (c) is selected from the memory 42 and read out.

  For this reason, when the flow rate is measured using the sensor body 15a after replacement (the combination shown in FIG. 5), as in the case of using the sensor body 15 before replacement (the combination shown in FIG. 1), As shown in FIG. 6, the flow rate can be displayed with a predetermined accuracy range (about ± 3% FS). That is, even if the sensor body is replaced, the measurement accuracy does not decrease. FIG. 6 is a diagram showing the relationship between the flow rate of the fluid and the flow rate display (measurement error) in the display unit.

As described above, a plurality of data tables are stored in the memory 42 of the display device 40, and a selection signal (voltage value) for selecting a data table suitable for the characteristics of the flow sensor 21 and the temperature sensor 22 in the sensor unit 20 is provided. By providing the voltage setting device 28 for setting, even if general-purpose products are used as the flow rate sensor 21 and the temperature sensor 22, the compatibility between the sensor main bodies 15 and 15 a (sensor units 20 and 20 a) and the display unit 40 is ensured. It is possible to ensure sufficient measurement accuracy.
This eliminates the need for the selection and dedicated production of the flow sensor and temperature sensor, which has been necessary in the past, and reduces the cost of the flow sensor and temperature sensor by about 80%. Therefore, the cost of the separation-type thermal flow meter 10 is also advantageous.

In addition, the abnormality notification unit 25 of the sensor unit 20 detects the presence or absence of abnormality based on a voltage (p signal) that changes according to the current flowing through the flow sensor 21. That is, the comparison circuit OP2 compares the p signal with the reference voltage, and when the p signal exceeds the reference voltage, the LED 29 is turned off to notify the outside that an abnormality has occurred.
Thus, in the separation-type thermal flow meter 10 according to the present embodiment, an abnormality display can be performed also in the sensor body 15 (sensor unit 20). As a result, even when the sensor unit 20 and the display unit 40 are installed apart from each other, it is possible to confirm whether or not there is an abnormality in the sensor unit 20, so that an abnormality is dealt with (for example, the fluid supply to the flow meter 10 is stopped) Etc.) can be carried out quickly. Therefore, it is possible to reliably avoid a situation where the abnormality detection is delayed and the flow meter 10 is damaged.

  Then, when 5 seconds have elapsed since the power was turned on, the signal processing unit 26 turns off the analog switch SW1 and turns on the analog switch SW2. As a result, a voltage (p signal) that changes according to the current flowing through the flow sensor 21 is output from the sensor unit 20 as a P signal. This p signal is input to the display unit 40 and monitored by the CPU 41. That is, the CPU 41 determines whether or not the p signal exceeds the upper limit value. When the p signal exceeds the upper limit value, the flow rate detection unit 23 of the sensor unit 20 may be damaged. Therefore, the transistor Tr2 is activated and the supply of the power supply voltage V + to the sensor unit 20 is stopped. . Thereby, when a large current flows through the bridge circuit of the flow rate detection unit 23, the power source of the sensor unit 20 is automatically turned off, so that the flow rate detection unit 23 can be reliably prevented from being damaged.

As described above in detail, in the separation type thermal flow meter 10 according to the present embodiment, characteristic variations that occur when general-purpose products are used for the flow sensor 21 and the temperature sensor 22 in the memory 42 of the display unit 40. Table data is stored in three types of data tables (a), (b), and (c), and table selection signals corresponding to the data tables (a), (b), and (c) are output to the sensor unit 20. Since the signal output unit 24 is provided, compatibility between different sensor bodies and the display unit 40 can be ensured even if a general-purpose product is used without selecting the flow sensor 21 and the temperature sensor 22 or making a dedicated production. And sufficient measurement accuracy can be obtained.
Further, in the separation type thermal flow meter 10 according to the present embodiment, since the abnormality notification unit 25 is provided in the sensor unit 20, the abnormality is notified by the LED 29 also in the sensor body 15 (sensor unit 20). be able to.

  It should be noted that the above-described embodiment is merely an example and does not limit the present invention in any way, and various improvements and modifications can be made without departing from the scope of the invention. For example, in the above-described embodiment, a rotary switch is used as the voltage setting device 28, but laser trimming processing may be performed.

  In the above-described embodiment, the abnormality is notified by turning off the LED 29. However, the abnormality may be notified by blinking. Moreover, abnormality can also be alert | reported by making LED two-color display and lighting the color different from the time of normal electricity supply.

It is a schematic block diagram of the separation-type thermal flow meter which concerns on embodiment. It is a circuit diagram which shows the circuit structure of a sensor part. It is a block diagram which shows the structure of a display part. It is a figure which shows the content of the data table memorize | stored in the memory of a display part. It is explanatory drawing explaining the state which connected the different sensor main body to the same display part. It is a figure which shows the relationship between the flow volume of a fluid, and the flow volume display (measurement error) in a display part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Separation-type thermal flow meter 11 Flow path 12 Body 15 Sensor main body 16 Cable 20 Sensor part 21 Flow rate sensor 22 Temperature sensor 23 Flow rate detection part 24 Table selection signal output part 25 Abnormality notification part 26 Signal processing part 27 Amplifier circuit 28 Voltage setting LED 29
40 display unit 41 CPU
42 memory

Claims (5)

A body part in which a flow path is formed, a sensor part that outputs a signal corresponding to a flow rate of fluid by a constant temperature difference circuit including a heater temperature detection resistor and a fluid temperature detection resistor installed in the flow path, and the sensor A display unit that calculates and displays a fluid flow rate based on an output signal from the unit, the sensor unit and the display unit are separated, and a power supply voltage is supplied from the display unit to the sensor unit In the type thermal flow meter,
The display unit includes a memory that stores a plurality of data tables representing a relationship between an output signal from the sensor unit and a fluid flow rate,
The sensor unit includes a table selection signal output unit that outputs one of the table selection signals associated with each of the plurality of data tables to the display unit,
When the table selection signal output from the sensor unit is input to the display unit, the display unit selects a data table corresponding to the table selection signal from the plurality of data tables and selects the data table. A separation type thermal flow meter that calculates a flow rate of a fluid based on a data table. In the separation type thermal flow meter according to claim 1,
The separation type thermal flow meter, wherein the table selection signal output unit has voltage setting means for presetting the table selection signal with a voltage value. In the separation type thermal flow meter according to claim 1 or 2,
The sensor unit determines that an abnormality has occurred in the heater temperature detection resistor when the voltage that changes according to the current flowing through the heater temperature detection resistor exceeds a preset reference voltage, A separation type thermal flow meter having an abnormality notifying unit for notifying. In the separation type thermal flow meter according to claim 3,
The sensor unit outputs a voltage value that changes according to a current flowing through the heater temperature detection resistor to the display unit,
The said display part stops supply of the power supply voltage to the said sensor part, when the said voltage value exceeds the preset upper limit, The separation-type thermal flowmeter characterized by the above-mentioned. In the separation type thermal flow meter according to claim 4,
The sensor unit outputs the table selection signal to the display unit when the power is turned on, and a voltage value that changes according to the current flowing through the heater temperature detection resistor after a predetermined time has elapsed since the power is turned on. A separation type thermal flow meter comprising a signal processing unit for outputting.

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