JPH0399273A - Hot-wire anemometer with deterioration prevention device - Google Patents

Abstract

PURPOSE:To maintain accuracy as long as possible by providing a means for switching move to cut heating current of a wind velocity sensor except when a need arises for measuring wind velocity of a current. CONSTITUTION:A wind velocity sensor 3 is so arranged that current flows therethrough according to a wind velocity and an MPU 53 computes a wind signal based on signals outputted to a data bath 51 to be displayed on a display device. For example, when there is soot containing melting ash in a combustion gas, it becomes more meltable as the temperature rises up to a high temperature facilitating the adherence of the soot to the wind velocity sensor 3. With the adhering of the soot, the outer diameter, namely, surface area of the wind velocity sensor 3 increases causing a change in transfer of heat from the wind velocity sensor 3 and hence, an electric output in the detection of wind velocity varies, which causes an error in a reading of the wind velocity. Thus, this problem can be reduced by lowering the temperature of the wind velocity sensor 3 to the temperature of wind thereby enabling the maintaining of the accuracy of the wind velocity sensor as long as possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hot wire anemometer with a deterioration prevention device, and in particular, a hot wire anemometer with a deterioration prevention device, in which a wind temperature sensor and a wind speed sensor are disposed in an air flow to be measured,
A deterioration prevention device that is equipped with a device that prevents deterioration of the wind speed sensor in a hot wire anemometer that measures airflow velocity and wind speed by controlling to give a temperature difference between the wind temperature sensor and the wind speed sensor. Regarding a hot wire anemometer with device.

[Prior Art] In boilers, heat treatment furnaces, incinerators, and the like, the temperature and flow velocity of airflow are measured in the furnace, flue, etc. in order to control combustion and exhaust gas. A hot wire anemometer is used for this measurement. A hot wire anemometer uses a thin resistance wire made of a platinum alloy, and includes a wind temperature sensor for measuring the temperature of the airflow, and a wind speed sensor that is heated and kept at a higher temperature than the temperature of the airflow.

Then, the temperature and flow velocity of the airflow are kept constant by controlling to provide a temperature difference between the wind temperature sensor and the wind speed sensor.

[Problems to be Solved by the Invention] By the way, when measuring the flow velocity and temperature of air in a furnace at a high temperature of close to 1000°C using a hot wire anemometer, the resistance coefficient does not deteriorate even if a platinum alloy that is resistant to high temperature deterioration is used. This is unavoidable, and when used for a long time, the wind speed indication will be incorrect. Furthermore, in the case of measuring the flow velocity of combustion exhaust gas, there is a drawback that soot and dust in the gas adheres to the sensor, inhibits heat conduction, and changes the wind velocity indication.

Therefore, it is an object of the present invention to provide a hot wire anemometer with a deterioration prevention device that can eliminate the above-mentioned obstacles and provide accurate wind speed indications over a long period of time.

[Means for Solving the Problem] The invention according to the first claim provides an air temperature sensor that is placed in an air flow to be fixed and measures the temperature of the air flow, and a temperature sensor that is heated to a temperature higher than that of the air flow. The wind temperature sensor and the wind speed sensor measure the air flow velocity and wind temperature by arranging a wind speed sensor maintained at a temperature and controlling the temperature difference between the wind temperature sensor and the wind speed sensor. The present invention is a hot wire anemometer with a deterioration prevention device for preventing deterioration of the wind speed sensor, and the hot wire anemometer is equipped with means for switching the heating current of the wind speed sensor to a mode other than when it is necessary to measure the wind speed of the airflow.

The invention according to claim 2 is configured to include means for passing a minute current through the wind speed sensor and switching to a mode for detecting a change in resistance of the wind speed sensor.

The invention according to claim 3 is configured to include means for heating the wind speed sensor to a high temperature capable of burning unnecessary materials and switching the mode to a mode in which unnecessary materials attached to the surface of the wind speed sensor are burned.

The invention according to claim 4 provides a first mode for measuring the wind speed and wind temperature of the airflow, a second mode for cutting off the heating current of the wind speed sensor except when it is necessary to measure the wind speed of the airflow, and a second mode for measuring the wind speed of the airflow. A third mode in which a minute current is applied to detect changes in the resistance of the wind speed sensor, and a fourth mode in which the wind speed sensor is heated to a high temperature that can burn unnecessary materials and the unnecessary materials attached to the surface of the wind speed sensor are burned. The device is configured to include means for switching to at least two or more of the modes.

[Function] The invention according to the first claim is configured to cut off the heating current of the wind speed sensor except when it is necessary to measure the wind speed of the airflow,
The temperature of the wind speed sensor can be lowered to the same level as the temperature of the airflow, and deterioration of the wind speed sensor can be prevented.

According to the second aspect of the invention, by passing a minute current through the wind speed sensor, changes in resistance can be detected from time to time during long-term use, which can be used to determine when to replace the wind speed sensor.

The invention according to claim 3 restores the sensitivity of the wind speed sensor and maintains its accuracy for a long time by heating the wind speed sensor to a high temperature that can burn unnecessary materials and burning the attached unnecessary materials. .

The invention according to claim 4 is capable of lowering the temperature of the wind speed sensor to the same level as the wind temperature sensor by cutting off the heating current of the wind speed sensor other than when it is necessary to measure the wind speed of the airflow. By applying a small current to detect resistance changes and heating the wind speed sensor to a high temperature that can burn unnecessary materials, unnecessary materials attached to the surface can be burned and deterioration of the wind speed sensor can be prevented.

[Embodiment of the Invention] FIG. 1 is a schematic block diagram of an anemometer instrument section according to an embodiment of the invention. FIG. 2 is a sectional view of a wind speed sensor used in an embodiment of the present invention.

There are various methods for maintaining the temperature difference between the wind speed sensor and the wind temperature sensor of a hot wire anemometer, such as a constant voltage method and a constant current method, but in this embodiment, a constant resistance method (constant temperature difference method) will be explained.

First, the configuration of the wind speed sensor will be described with reference to FIG. 2. The probe 2 measures the wind speed and temperature of the airflow 1 in the flue, and is inserted into the flue by providing an insertion port in the flue side wall 14 and the insulation 915 that constitute the flue. In other words, the probe 2 is fixed to the flue side wall 14 via the flange 12 and the flue side flange 13. The probe 2 includes a protection tube 6, and this protection tube 6
An inlet window 7a through which the airflow 1 enters and an outlet window 7b are formed in the. Further, a wind speed sensor 3 and a wind temperature sensor 4 are mounted inside the protection tube 6 with heat-resistant cement 5.

The wind speed sensor 3 consists of a thin tube with a heating resistance wire provided inside. By passing a heating current through this resistance wire,
The temperature of the wind speed sensor 3 is kept higher than the temperature of the airflow 1, which is determined by Δ-1. The air temperature sensor 4 is provided to measure the temperature of the air flow 1.

The wind speed sensor 3 and the wind temperature sensor 4 are connected to a terminal box 9 via a lead wire 8 provided inside the protection tube 6. Inside the terminal box 9, the lead wires 8 are connected to respective connection terminals 10, and the lead wires 11 extending from the terminal box 5 are connected to the connection terminals 10.

Next, the circuit configuration of the anemometer instrument section shown in FIG. 1 will be explained. A minute current of, for example, 5 mA is supplied from the constant current 7119f44 to the wind temperature sensor 4 through the relay contact 43, and the voltage across the wind temperature sensor 4 is detected by the wind temperature sensor voltage detection circuit 25. The output of the wind temperature sensor voltage detection circuit 25 is given to a voltage adder 27 and an A/D converter 20. An additional voltage is applied to the voltage adder 27 via a relay contact 48 from an additional voltage generator 26 consisting of a resistor that divides the power supply voltage. This additional voltage generator 26 generates an additional voltage in order to keep the temperature of the wind speed sensor 3 higher than the temperature of the wind temperature sensor 4 by about 100°C.

This added voltage is also applied to the A/D converter 20.

The voltage adder 27 adds the voltage generated from the addition voltage generator 26 to the output voltage of the wind temperature sensor voltage detection circuit 25,
It is applied to one input terminal of the proportional stability amplifier 28 via the relay contact 45.

On the other hand, the wind speed sensor 3 is connected to a constant voltage source 49 by a transistor 29. A current is supplied through the relay contact 42 and the detection resistor 22, and the voltage across the wind speed sensor 3 is detected by the wind speed sensor voltage detection circuit 24, and the detected voltage is A.
/D converter 20 and divider 50. The voltage across the detection resistor 22 is detected by the heating current detection circuit 23, and the detected voltage is provided to the A/D converter 20 and the divider 50. The divider 50 converts the detection voltage output from the wind speed sensor voltage detection circuit 24 into the heating current detection circuit 2.
3 by the given detection voltage, and a voltage corresponding to the resistance value of the wind speed sensor 3 is applied to the other input terminal of the proportional stability amplifier 28.

The output of the proportional stability amplifier 28 is a PNP) transistor 29
A constant voltage is applied to the emitter of this transistor 29 from a constant voltage source 49, and the collector is connected to the detection resistor 22 via a relay contact 42.

A burn voltage is applied from a burn voltage generator 47 via a relay contact 46 to one input terminal of the proportional stability amplifier 28 mentioned above. This burn voltage increases the temperature of the wind speed sensor 3 to 700℃.
The voltage is selected to be equivalent to a resistance that heats the wind speed sensor 3 to 700°C.

Relay contact 41 is closed when in resistance comparison mode;
A constant current is supplied from the constant current source 40 to the wind speed sensor 3 via the relay contact 41 and the resistor 22.

The A/D converter 20 converts the detection voltage of the heating current detection circuit 23, the detection voltage of the wind speed sensor voltage detection circuit 24, the detection voltage of the wind temperature sensor voltage detection circuit 25, and the voltage from the addition voltage generator 26 into digital signals, respectively. and provides it to the data bus 51. The data bus 51 has a program RO
M52, MPU53, characteristic ROM54, and display 55 are connected. The MPU 53 calculates a wind speed signal based on each detection signal according to a program stored in advance in the program ROM 52 and causes the display 55 to display the wind speed signal.

FIG. 3 is a table showing the operation of each relay contact shown in FIG. 1.

Next, the specific operation of one embodiment of the present invention will be explained. First, in the wind speed measurement mode in which the wind speed sensor 3 measures the wind speed, the relay contacts 42, 43, 45 and 48 are respectively closed, and the relay contacts 41, 46 are opened. Since the relay contact 43 is closed,
The air temperature sensor 4 is connected to the constant current source 44 via the relay contact 43.
A constant current is supplied to the wind temperature sensor 4 , the voltage across the wind temperature sensor 4 is detected by the wind temperature sensor voltage detection circuit 25 , and the detected voltage is converted into a digital signal by the A/D converter 20 and given to the data bus 51 .

Further, the detected voltage of the wind temperature sensor voltage detection circuit 25 is provided to a voltage adder 27. The addition voltage generator 26 generates a voltage corresponding to the temperature difference in order to keep the temperature of the wind speed sensor 3 approximately 100° C. higher than the temperature of the wind temperature sensor 4.

With the relay contact 48 closed, this voltage is converted into a digital signal by the A/D converter 20 and applied to the data bus 51 as well as to the voltage adder 27. Voltage adder 27 adds the voltage from addition voltage generator 26 to the detected voltage of wind temperature sensor voltage detection circuit 25, and applies the added voltage to proportional stability amplifier 28 by closing relay contact 45. Also, since the relay contact 42 is closed, the constant voltage source 49
A constant voltage is applied to the transistor 29. It is applied to the wind speed sensor 3 via the relay contact 42 and the resistor 22.

The voltage across the wind speed sensor 3 is determined by the wind speed sensor voltage detection circuit 24.
The detected voltage is detected by the A/D converter 2.
0 is converted into a digital signal and sent to the data bus 51.
and also to the divider 50. In addition, the voltage across the detection resistor 22 is detected by the heating current detection circuit 23, and the detected voltage is given to the divider 50, converted into a digital signal by the A/D converter 20, and output to the data bus 51. . Divider 5
0 is calculated by dividing the detection voltage of the wind speed sensor voltage detection circuit 24 by the detection voltage of the addition current detection circuit 23 to generate a proportional stable amplifier 28.
give to The proportional stability amplifier 28 provides a signal to the transistor 29 such that the voltage from the voltage adder 27 and the voltage from the divider 50 are balanced, and controls the current flowing from the constant voltage source 49 to the wind speed sensor 3.

As described above, a current according to the wind speed flows to the wind speed sensor 3, and when the wind temperature changes, the wind temperature sensor 4 at that time
Since a constant voltage from the addition voltage generator 26 is added to the detection voltage of the wind temperature sensor voltage detection circuit 25 in accordance with the resistance change, a constant temperature difference is always maintained between the wind speed sensor 3 and the wind temperature sensor 4. is retained. Furthermore, the MPU 53 calculates a wind speed signal based on each signal output to the data bus 51 and displays it on the display 55.

Next, the non-measurement mode will be explained. In the non-measuring mode, each of the relay contacts 41, 42, 43, 45, 46 and 48 are opened. As a result, the current supplied to the wind speed sensor 3 and the wind temperature sensor 4 is cut off, and the temperature drops to the same temperature as the wind temperature. The electrical resistance characteristics of a PT-based sensor are somewhat stable even at temperatures around 1000° C., but when used for a long time, there is a risk that the characteristics will gradually deteriorate and change, and the changes become more severe as the temperature increases. In particular, since the wind speed sensor 3 is maintained at a temperature approximately 100°C higher than the wind temperature sensor 4,
The changes are large, so by lowering this to the wind temperature, the changes can be suppressed as much as possible.

Since only a weak current flows through the wind temperature sensor 4, it is originally at the same temperature as the wind temperature, but it is preferable to shut it off for the sake of circuit balance.

Furthermore, if there is soot dust containing molten ash in the combustion gas, the higher the temperature, the more molten it becomes and the more likely it is to adhere to the wind speed sensor 3. When dust adheres, the outer diameter, ie, the surface area, of the wind speed sensor 3 increases, so the amount of heat transferred from the wind speed sensor 3 changes. Therefore, the electrical output for wind speed detection changes, and an error occurs in the indicated value of the wind speed. Therefore, by lowering the temperature of the wind speed sensor 3 to the wind temperature, this adverse effect is also reduced, and the accuracy of the wind speed sensor 3 can be maintained for as long as possible.

Next, the resistance comparison mode will be explained. In resistance comparison mode, only relay contacts 41,43 are closed;
The other relay contacts 42.45° 46 and 48 are opened. By closing the relay contacts 41 and 43, a constant current is supplied to the wind temperature sensor 4 from the constant current source 44, and a weak current is supplied to the wind speed sensor 3 from the constant current source 40.

When a weak current flows through the wind speed sensor 3, the voltage across it is detected by the wind speed sensor voltage detection circuit 24, the voltage across the wind temperature sensor 4 is detected by the wind temperature sensor voltage detection circuit, and each is digitally converted by the A/D converter 20. It is converted into a signal and output to the data bus 51.

The MPU 5B takes in the signal output to the data bus 51, and while the hot wire anemometer is used for a long time, it can occasionally detect changes in the resistance characteristics of the wind speed sensor 3, and corrects the measured wind speed and adjusts the wind speed sensor 3. It can be used to determine when to replace it. In addition, a correction calculation formula program is stored in advance in the program ROM 52, and the correction calculation is automatically performed by the MPU 53, so that the wind speed sensor 3 can be used without replacing the wind speed sensor 3 in response to a slight change in resistance value. It is also possible to continue.

Next, the incineration mode will be explained. In incineration mode, relay contacts 42 and 46 are closed and other relay contacts 41, 43, 45 and 48 are opened. By closing the relay contact 46, a voltage corresponding to the resistance required to heat the wind speed sensor 3 to about 700° C. is applied from the burn voltage generator 47 to the comparative stability amplifier 28.

Comparison stability amplifier 28 provides a signal to transistor 29 in response to the voltage provided from burn voltage generator 47. In response, the two transistors cause current to flow from the constant voltage source 49 to the wind speed sensor 3 via the relay contact 42 and the resistor 22, heating the wind speed sensor 3 to approximately 700°C. When the combustion gas contains carbonaceous soot at a temperature of about several hundred degrees centigrade, it is burned and removed by heating to a temperature suitable for incinerating the adhering soot, for example, 700 degrees centigrade. By repeating this operation in a timely manner, the sensitivity of the wind speed sensor 3 can be restored and accuracy can be maintained for a long time.

In addition, the above-mentioned relay contacts 41, 42, 43, 45, 46
and 48 may manually drive a relay coil to close each contact, or a sequencer may be provided to switch each relay contact according to each mode.

[Effects of the Invention] As described above, the invention according to the first claim cuts off the heating current of the wind speed sensor except when it is necessary to measure the wind speed of the airflow, so that the temperature of the wind speed sensor can be changed from the temperature of the airflow. It is possible to maintain the same level, reduce the degree of soot and dust adhering to the wind speed sensor, and maintain the accuracy of the wind speed sensor for as long as possible.

According to the invention according to the second claim, since a minute current is passed through the wind speed sensor to detect a change in resistance of the wind speed sensor, it can be useful for correcting the measured wind speed and determining when to replace the wind speed sensor. .

According to the third aspect of the invention, the temperature of the wind speed sensor is set to a high enough temperature to burn unnecessary materials, so that the unnecessary materials attached to the surface are burned, thereby recovering the sensitivity of the wind speed sensor and maintaining accuracy for a long time. can do.

According to the fourth aspect of the invention, the heating current of the wind speed sensor is cut off when it is not necessary to measure the wind speed of the air current, or a minute current is passed through the wind speed sensor to detect a resistance change of the wind speed sensor, or the wind speed sensor By heating the wind speed sensor and burning off unnecessary substances attached to the surface, the sensitivity of the wind speed sensor can be restored and accuracy can be maintained for a long time.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an embodiment of the present invention. FIG. 2 is a sectional view of a probe included in the hot wire anemometer. FIG. 3 is a table showing the open/close states of the relay contacts in each mode. In the figure, 1 is an air flow, 2 is a probe, 3 is a wind speed sensor, 4 is a wind temperature sensor, 22 is a detection resistor, 23 is a heating current detection circuit, 24 is a wind speed sensor voltage detection circuit, and 25 is a wind temperature sensor voltage detection circuit , 26 is a summing voltage generator, 27 is a voltage adder, 28 is a proportional stable amplifier, 29 is a transistor,
40.44 is a constant current source, 41, 42.43, 45, 46
．． 48 is a relay contact, 47 is a burn voltage generator, 4 is a constant voltage source, and 50 is a divider.

Claims (4)

[Claims] (1) A wind temperature sensor that is placed in the airflow to be measured and measures the temperature of the airflow, and a wind speed sensor that is heated and kept at a higher temperature than the temperature of the airflow, and the temperature measurement sensor A hot wire anemometer with a deterioration prevention device that prevents deterioration of the wind temperature sensor and the wind speed sensor, in which the flow velocity and wind temperature of the air current are measured by controlling to give a temperature difference between the wind temperature sensor and the wind speed sensor. The hot wire anemometer with a deterioration prevention device is provided with means for switching to a mode for cutting off the heating current of the wind speed sensor except when it is necessary to measure the wind speed of the airflow. (2) an air temperature sensor that measures the temperature of the airflow to be measured;
A wind speed sensor that is heated and maintained at a temperature higher than that of the air flow is arranged, and the flow velocity of the air flow is controlled by controlling to give a temperature difference between the wind temperature sensor and the wind speed sensor. A hot wire anemometer with a deterioration prevention device that prevents deterioration of the wind temperature sensor and the wind speed sensor for measuring temperature, a mode in which a minute current is passed through the wind speed sensor and a change in resistance of the wind speed sensor is detected. provided with means for switching to
Hot wire anemometer with deterioration prevention device. (3) A wind temperature sensor that is placed in the airflow to be measured and measures the temperature of the airflow, and a wind speed sensor that is heated and maintained at a higher temperature than the temperature of the airflow, and the wind temperature sensor A hot wire anemometer with a deterioration prevention device that prevents deterioration of the wind speed sensor, the hot wire anemometer measuring the flow velocity and wind temperature by controlling to give a temperature difference between the wind speed sensor and the wind speed sensor, Set the wind speed sensor to a high temperature that can burn waste materials,
A hot wire anemometer with a deterioration prevention device, which is equipped with a means for switching to a mode in which unnecessary matter adhering to the surface of the wind speed sensor is burned. (4) A wind temperature sensor that is placed in the airflow to be measured and measures the temperature of the airflow, and a wind speed sensor that is heated and kept at a higher temperature than the temperature of the airflow, and the wind temperature sensor A hot wire anemometer with a deterioration prevention device that prevents deterioration of the wind temperature sensor and the wind speed sensor, in which the flow velocity and wind temperature of the air are measured by controlling to give a temperature difference between the wind speed sensor and the wind speed sensor. a first mode in which the wind speed and wind temperature of the airflow are measured; a second mode in which the heating current of the wind speed sensor is cut off except when it is necessary to measure the wind speed of the airflow; A third mode in which a current is applied to detect a change in resistance of the wind speed sensor; and a fourth mode in which the wind speed sensor is heated to a high temperature capable of burning unnecessary materials, and unnecessary materials attached to the surface of the wind speed sensor are burned. A hot wire anemometer with a deterioration prevention device, comprising means for switching to at least two or more of the modes.