JP2007147495A - Atmosphere analyzer - Google Patents

Abstract

An atmosphere analyzer that is less susceptible to noise and that can further reduce the size of a detection unit.
An atmosphere analyzer including a sensor unit, a control unit, and a connection path, wherein the sensor unit includes a reference crystal resonator, sealed in an airtight container, A crystal oscillator 45 for detection held so as to be exposed to the detection substance, two oscillation circuits 43 and 46 for oscillating the two crystal oscillators, and two oscillation circuits using an up / down counter 50 Frequency difference circuits 53 and 54 that count a value corresponding to the frequency difference, convert the counted value into a frequency difference conversion signal, and output the converted signal.
[Selection] Figure 2

Description

  The present invention relates to an atmosphere analysis apparatus using a QCM (Quartz Crystal Microbalance) sensor, and more particularly to improvement of a signal transmission and control method in an atmosphere analysis apparatus having a sensor unit and a control unit that can be installed at remote positions.

  The QCM sensor utilizes the fact that the oscillation frequency of a crystal resonator changes due to a mass change based on substance adsorption on the surface of the resonator, and is applied as a highly sensitive atmosphere analysis device.

  FIG. 1 is a diagram showing a configuration of a conventional highly sensitive atmosphere analyzer.

  As shown in the drawing, the atmosphere analyzer includes a sensor circuit board 10 that constitutes a detection unit, a control unit 20 that constitutes a control unit, and a cable 31 that electrically connects the sensor circuit board 10 and the control unit 20. , 32. The sensor circuit board 10 is provided with a crystal resonator 11 provided with a material on which a substance to be detected is adsorbed on the surface, and a crystal oscillation circuit 12 that oscillates using the crystal resonator 11. The control unit 20 is provided with a frequency counter 21 that receives the oscillation signal of the crystal oscillation circuit 12 via the signal transmission line 32 and counts the oscillation signal, and a recording circuit 22 that records the value counted by the frequency counter 21. It has been. The power for the sensor circuit board 10 is supplied from the control unit 20 via the power supply line 31.

  The atmosphere analyzer shown in FIG. 1 has several drawbacks. One drawback is the temperature dependence of the oscillation frequency. Even if the oscillation frequency changes, it cannot be distinguished whether the cause is a change in air concentration or a change in temperature, so it cannot be used in a system with a change in temperature. For the purpose of temperature compensation, there is an example in which a crystal oscillator and a temperature sensor are arranged side by side and the change in the oscillation frequency of the crystal oscillator is corrected using a known temperature-oscillation frequency curve. However, the correction was not successful compared to the complexity of the circuit.

  Another disadvantage is that the degree of freedom of installation location of the sensor circuit board is low. This is mainly due to the signal transmission line 32. Since the oscillation frequency of the crystal oscillation circuit 12 using a crystal resonator is several tens of MHz, a coaxial cable is used for the signal transmission line 32 for transmitting a signal from the sensor substrate circuit 10 to the control unit 20 in order to suppress transmission loss. There was a need. As a recent requirement for an atmospheric analyzer, it is necessary to measure the atmospheric change in a sealed narrow space. In order to install the sensor circuit board 10 there, high-frequency transmission is performed on the wall of the sealed container. It was necessary to install a feed-through that could not be installed, which was an obstacle to installation. Another problem is that the coaxial cable is thick and poor in flexibility. There is also a method of wireless transmission as described in Patent Document 1, but there are problems of increasing the size of the apparatus and securing a power source. Although a method of wiring through a flexible cable through the gap between the sealed containers is also conceivable, there is a problem that transmission loss in the flexible cable is large and stability of the entire circuit is lowered. Since the control unit 20 having the sensor circuit board 10 and the frequency counter 21 is installed at a distant position, the problem of transmission loss is fatal.

  In order to solve the above-mentioned two drawbacks, Patent Documents 2 to 4 disclose a quartz crystal for detection exposed to a substance to be detected, a detection oscillation circuit thereof, and a reference crystal provided so as not to be exposed to the substance to be detected. A vibrator and its reference oscillation circuit, and a frequency difference detection circuit for detecting the oscillation frequency difference between the detection oscillation circuit and the reference oscillation circuit are provided, and the effect of temperature change is canceled by detecting the difference between the two oscillation frequencies. In addition, a configuration is described in which the numerical value of the detected frequency is reduced. Patent Document 2 describes a frequency difference detection circuit configured by a DK flip-flop, and Patent Document 2 describes a frequency difference detection circuit configured by a beat frequency detection circuit. Patent Document 3 describes that the frequency difference detection circuit is configured by a multiplication & sampling & frequency dividing circuit, but does not describe a specific configuration.

  If the configuration described in Patent Documents 2 to 4 is provided on the sensor circuit board, the output frequency difference detection signal has a low frequency, and therefore can be transmitted to the control unit through a flexible cable, a twisted pair wire, or the like. As described above, if the configurations described in Patent Documents 2 to 4 are used, the above-described two drawbacks are improved.

JP 2004-047929 A JP-A-9-304259 JP-A-6-167435 Japanese Patent Laid-Open No. 9-297096

  The frequency difference detection signal indicating the frequency difference between the two crystal oscillation signals in the above configuration is at most several hundred Hz, and the control unit monitors the transmitted difference signal. Since the frequency difference detection signal is such a low frequency, it can be transmitted via a flexible cable without using a coaxial cable, etc., but conversely, the frequency difference is small, so it is easily affected by ambient noise. There is. Disturbances that generate noise or the like in the transmission signal occur suddenly, and their generation period is generally short. When a very low frequency signal as described above is monitored, it is necessary to monitor the signal for a certain period of time and count the pulses. However, as the count period becomes longer, the probability of being affected by noise increases accordingly.

  In addition, the sensor circuit board is required to be as small as possible so that it can be arranged in a narrow space. If the configurations described in Patent Documents 3 and 4 are used, the difference between the two oscillation frequencies is detected, so the numerical value of the detected frequency is small, and the number of digits of the counter can be reduced. However, when a circuit is actually formed, it is difficult to completely suppress variations in various elements, and the number of digits of the counter is set with an allowance on the assumption that the oscillation frequency difference varies to some extent. Therefore, there has been a problem that the circuit cannot be sufficiently reduced in size.

  The present invention solves such a problem, and an object of the present invention is to provide an atmosphere analyzer that is less susceptible to noise and that can further reduce the size of a detection unit.

  In order to achieve the above object, the atmosphere analyzer of the present invention uses an up / down counter to count a value corresponding to a frequency difference between two oscillation circuits, and the counted value is a frequency difference conversion signal of a low frequency signal. To output in a short time. Further, the length of the count period can be controlled from the control unit.

  That is, the atmosphere analyzer of the present invention can be provided in a sensor unit disposed in an atmosphere having a substance to be detected, a position away from the sensor unit, and a control unit that controls the sensor unit; An atmosphere analysis device comprising a connection path for electrically connecting the sensor unit and the control unit, wherein the sensor unit has substantially the same characteristics, and one is exposed to the substance to be detected. And the other is a frequency difference between the two oscillation circuits using an up / down counter and two oscillation circuits for oscillating the two quartz oscillators. A frequency difference circuit that counts a value corresponding to the first predetermined period, converts the counted value into a frequency difference conversion signal, and outputs it during a second predetermined period shorter than the first predetermined period, and the connection path Said Characterized in that it is a low frequency of transmitting the frequency signal.

  The control unit changes the length of the first predetermined period according to the detected frequency difference conversion signal.

  In the atmosphere analyzer of the present invention, the value corresponding to the frequency difference counted using the up / down counter is counted, and the counted value is not a high frequency such as several tens of MHz, but a flexible cable or a twisted pair wire. Since it is converted into a frequency difference conversion signal having a relatively low frequency in the frequency range that can be transmitted through the connection path, it is less susceptible to noise than a high frequency such as several tens of MHz.

  In addition, by enabling the control unit to start and stop the frequency difference counting using the up / down counter, that is, to control the counting period, the circuit capacity can be maximized even if the circuit elements vary. As a result, the circuit scale can be substantially reduced, and detection can always be performed with good accuracy.

  As described above, when the signal is counted by the counter, the number of digits of the counter is set with a margin in consideration of variations in the signal frequency. For example, if counter overflow occurs, correct counting cannot be performed. In the configurations described in Patent Documents 3 and 4, the counter period and the like are fixed, and it is necessary to set the number of digits of the counter with a margin, and the circuit is correspondingly large. On the other hand, according to the present invention, since the count period is set by the control unit, the count period is shortened when the counter is likely to overflow, and conversely, the count period is lengthened when the counter count value is small. Always use the full power of the circuit. Therefore, it is not necessary to set the number of digits of the counter with a margin, and the circuit can be further reduced in size.

  According to the present invention, it is possible to use a thin cable that is resistant to temperature changes and rich in flexibility, and further maintains the same advantages as the conventional atmosphere analyzer that the degree of freedom of the detection unit is high. While being less susceptible to noise, highly accurate detection is possible, and the detection unit can be further miniaturized.

  FIG. 2 is a diagram showing the configuration of the atmosphere analyzer according to the embodiment of the present invention.

  As shown in the drawing, the atmosphere analyzer of the embodiment is electrically connected between the sensor circuit board 40 constituting the detection unit, the control unit 60 constituting the control unit, and the sensor circuit board 40 and the control unit 60. Cables 71 to 73 such as flexible cables and twisted pair wires. The sensor circuit board 40 is provided in a sealed container 42 and is not exposed to a substance to be detected, a reference crystal oscillator 41 that oscillates using the reference crystal oscillator 41, and a reference crystal oscillator. 41. Although it has substantially the same characteristics as 41, a material for adsorbing the substance to be detected is provided on the surface, and the quartz crystal for detection 45 exposed to the atmosphere containing the substance to be detected and the quartz crystal for detection 45 are used. And a detection crystal oscillation circuit 46 that oscillates, an up / down counter 50, three AND gates 51, 52, and 56, a comparator 53, a low-frequency oscillation circuit 54, and an inverter 55 are provided. ing. The wiring is as shown. Further, since the reference crystal oscillator 41, the reference crystal oscillation circuit 43, the detection crystal oscillator 45, and the detection crystal oscillation circuit 46 are described in Patent Documents 1 to 4 and the like, detailed description thereof is omitted. The reference oscillation signal and the detection oscillation signal output from the reference crystal oscillation circuit 43 and the detection crystal oscillation circuit 46, respectively, are as close as possible at the start of measurement, and the frequency of the reference oscillation signal is at least higher than the detection oscillation signal. It must be a frequency. It is desirable that the reference crystal unit 41 and the detection crystal unit 45 be arranged as close as possible. The low frequency oscillation circuit 54 outputs a transmission oscillation signal having a frequency that can be transmitted by the cable 72, for example, 1 kHz. The comparator 53 monitors the count value of the up / down counter 50, and outputs a signal for stopping the oscillation of the low frequency oscillation circuit 54 when the count value is zero.

  The control unit 60 is provided with a control circuit 61 and a recording circuit 62. The control circuit 61 supplies power to the sensor circuit board 40 via a cable 71 corresponding to a power supply line, and outputs a control signal for instructing measurement start and frequency transmission start via the cable 73, A counting pulse is received from the circuit board 40 via the cable 72.

  FIG. 3 is a flowchart illustrating the control operation of the atmosphere analyzer according to the embodiment. Hereinafter, the operation of the atmosphere analyzer of the embodiment will be described with reference to FIG.

  The reference crystal oscillation circuit 43 and the detection crystal oscillation circuit 46 always oscillate, and output a reference oscillation signal and a detection oscillation signal, respectively. In general, the crystal unit for detection 45 is provided with a material on which the substance to be detected is adsorbed and exposed to the atmosphere containing the substance to be detected, so that the mass increases. Even when the frequency is substantially the same as the frequency of the reference oscillation signal, the frequency gradually decreases with the passage of time, and the frequency difference gradually increases.

  In step 101, the control circuit 61 sets the control signal (data transfer control bit) output to the cable 73 to “H”. In response to this, the reference oscillation signal is input from the AND gate 51 to the down pulse input terminal DOWN of the up / down counter 50, and the detected oscillation signal is input from the AND gate 52 to the up pulse input terminal UP of the up / down counter 50. The up / down counter 50 starts to count the difference in the number of pulses corresponding to the frequency difference between the reference oscillation signal and the detected oscillation signal. As described above, since the frequency of the reference oscillation signal is higher than the frequency of the detection oscillation signal, the up / down counter 50 gradually decreases.

  In step 102, it is determined whether t seconds of the first predetermined period have elapsed from the start of measurement. The process waits until t seconds elapse, and proceeds to step 103 when t seconds elapse. In other words, the counting operation of the up / down counter 50 is performed for t seconds of the first predetermined period.

  In step 103, the control circuit 61 sets the data transfer control bit output to the cable 73 to “L”. In response to this, the input of the reference oscillation signal and the detection oscillation signal to the up / down counter 50 is stopped. At the same time, the output of the inverter 55 becomes “H”, the transmission oscillation signal output from the low frequency oscillation circuit 54 is input from the AND gate 56 to the up pulse input terminal UP of the up / down counter 50, and the cable 72 to the control circuit 61.

  When the transmission oscillation signal is input to the up pulse input terminal UP, the up / down counter 50 counts the number of pulses for t seconds of the reference oscillation signal and the detection oscillation signal until the count value that has been down becomes zero. The counting operation is continued until the difference (frequency difference) is counted. When the comparator 53 detects that the count value has become zero, the low-frequency oscillation circuit 54 stops oscillating. Therefore, the count value of the up / down counter 50 stops at zero. The time until the count value becomes zero, that is, the second predetermined period, is shorter than the first predetermined period because the frequency of the transmission oscillation signal is larger than the frequency difference between the reference oscillation signal and the detection oscillation signal.

  On the other hand, the control circuit 61 sets the control signal output to the cable 73 at step 103 to “L”, and simultaneously proceeds to step 104 to start counting the number of pulses of the oscillation signal for transmission.

  In step 105, the control circuit 61 detects whether or not the state in which the transmission oscillation signal is not transmitted continues for 2 ms or more, and continues counting the number of pulses until such a state is detected. Therefore, the control circuit 61 counts the difference in the number of pulses (frequency difference) for t seconds between the reference oscillation signal and the detection oscillation signal.

  In step 106, the control circuit 61 determines whether the counted number of pulses is close to the upper limit of the count value of the up / down counter 50. If it is close to the upper limit, the process proceeds to step 107, and the value of t used in step 102 is set. After decreasing by a predetermined amount, the process proceeds to step 108. If not close, the process proceeds to step 108 as it is.

  In step 106, the control circuit 61 determines whether the counted number of pulses is close to a predetermined lower limit set in advance by the up / down counter 50. After increasing the value by a predetermined amount, go to step 110. If not close, proceed to step 110 as it is.

  As described above, by adjusting t based on the count value, it is possible to always perform measurement under optimum conditions.

  In step 110, the control circuit 61 calculates the frequency difference by dividing the counted number of pulses by t used in step 102, and records it in the recording circuit 62 together with the time.

  In step 111, it is determined whether or not to continue the operation of measuring the frequency difference between the reference oscillation signal and the detected oscillation signal, and if so, the process returns to step 101 and the above operation is repeated. When the operation is not continued, it ends.

  Since the frequency of the low-frequency oscillation circuit 54 is about 1 kHz and the frequency difference between the two oscillation signals is about several hundred Hz at most, it takes less than 1 second to transmit the count difference. Considering the time response speed, this transmission time loss is negligible.

  Further, since the frequency difference between the two oscillation signals is about several hundreds Hz at most, the number of digits of the up / down counter 50 may be small. For example, a decimal counter may have four digits. The same applies to the counter in the control circuit 61.

  Since the signal used for transmission to the control circuit 61 is a low-frequency pulse from the low-frequency oscillation circuit 54, it can be transmitted by a flexible cable or twisted pair copper wire without using a coaxial cable, and the transmission loss is small. Because it is resistant to noise, fewer malfunctions occur. The distance between the sensor circuit board 40 and the control unit 60 can be charged and separated. Moreover, the number of cables may be two in addition to the power supply line. Further, when the frequency difference is 100 Hz, t is 1 second, and the count value is 100, the time required for transmission is 0.1 second, which is less susceptible to noise than when counting for 1 second or more. .

  The present invention is applicable to any apparatus as long as it is an atmosphere analyzer that detects a change in the frequency of an oscillation signal.

FIG. 1 is a diagram showing a configuration of a conventional atmosphere analyzer. FIG. 2 is a diagram showing the configuration of the atmosphere analyzer according to the embodiment of the present invention. FIG. 3 is a flowchart showing the control operation of the atmosphere analyzer according to the embodiment.

Explanation of symbols

40 Detection unit (sensor circuit board)
41 Reference Crystal Oscillator 42 Sealed Container 43 Reference Crystal Oscillator 45 Detection Crystal Oscillator 46 Crystal Oscillator for Detection 50 Up / Down Counter 54 Low Frequency Oscillator 60 Control Unit 61 Control Circuit

Claims (2)

A sensor unit disposed in an atmosphere having a substance to be detected;
A control unit that can be provided at a position away from the sensor unit and controls the sensor unit;
An atmosphere analyzer comprising: a connection path for electrically connecting the sensor unit and the control unit;
The sensor unit is
Two quartz crystal resonators having substantially equal characteristics, one held to be exposed to the substance to be detected and the other sealed in an airtight container;
Two oscillation circuits for oscillating the two crystal resonators;
A value corresponding to the frequency difference between the two oscillation circuits is counted for a first predetermined period using an up / down counter, and the counted value is converted into a frequency difference conversion signal to be a second predetermined period shorter than the first predetermined period. A frequency difference circuit that outputs during the period,
The atmosphere analyzer according to claim 1, wherein the connection path is for low frequency transmission of the low frequency signal.   The atmosphere analysis apparatus according to claim 1, wherein the control unit changes the length of the first predetermined period according to the detected frequency difference conversion signal.

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