JP4672277B2 - measuring device - Google Patents

Description

  The present invention relates to a measuring apparatus including a flying capacitor and a semiconductor switch.

  2. Description of the Related Art Conventionally, a temperature measurement device that detects the temperature at each measurement point using a plurality of thermocouples is known (see Patent Document 1).

  Such a temperature measuring device connects a semiconductor switch to each thermocouple, and controls each semiconductor switch to turn on and off, thereby sequentially extracting the voltage output from each thermocouple and measuring the temperature at each measurement point by 1 It is designed to be performed by two measuring units.

  However, such a temperature measuring device has a problem that it cannot measure the temperature at each measurement point at the same time because it has only one measuring unit.

  Therefore, as shown in FIG. 3, there has been proposed a temperature measuring device that can simultaneously measure the temperature at each measurement point using flying capacitors C1 and C2.

  In this temperature measuring device, the semiconductor switches S1, S3, S1 ′, S3 ′ are turned on, and the voltages output from the thermocouples T1, T2 are applied to the flying capacitors C1, C2 to be charged. Thereafter, the semiconductor switches S1, S3, S1 ′, S3 ′ are turned off, the semiconductor switches S2, S4 are turned on, and the temperature measured by the thermocouple T1 is obtained by a measuring unit (not shown).

Next, the semiconductor switches S2 and S4 are turned off, the semiconductor switches S2 'and S4' are turned on, and the temperature measured by the thermocouple T2 is obtained by a measurement unit (not shown). In this way, a plurality of measurement points can be measured simultaneously.
JP-A-8-144837

  However, in such a temperature measurement device, a common mode voltage Vc (unnecessary voltage) such as a commercial frequency band is superimposed on the measurement voltage Vn. Therefore, when the semiconductor switches S1 and S3 are turned on, the measurement voltage Vn is sampled in the flying capacitor C1, and at the same time, the stray capacitances Cf2 and Cf4 of the semiconductor switches S2 and S4 are charged by the common mode voltage Vc.

  Then, after the semiconductor switches S1 and S3 are turned off, the semiconductor switches S2 and S4 are turned on, but it is impossible to turn on the semiconductor switches S2 and S4 at the same time, and there is a time lag of about 0.1 msec. Arise. For this reason, for example, when the semiconductor switch S2 is turned on after the semiconductor switch S4 is turned on, the charge charged in the stray capacitance Cf2 flows into the flying capacitor C1 simultaneously with the turning on of the semiconductor switch S4. This affects the sampling voltage of the flying capacitor C1.

V ′ = Vc × Cf2 / (Cf2 + C1)
However, Vc is the voltage of the stray capacitance Cf2. Since the stray capacitance Cf2 is about 5 PF and C1 is 1 μF, the influence on the flying capacitor C1 is compressed to 1/200000, but the common mode voltage Vc is several tens of volts. The influence on the measurement of the order of μV is large.

  Further, when measuring the voltage of the flying capacitor C1, in order to turn off the semiconductor switches S1 and S3 and turn on the semiconductor switches S2 and S4, an arrow is applied to the line L by the common mode voltage Vc via the stray capacitance Cf3 of the semiconductor switch S3. As shown in FIG. The current IG causes a voltage to be generated in the line L because the line L has a resistance, and this voltage is superimposed on the measurement voltage. For this reason, there was a problem that accurate measurement could not be performed.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a measuring device capable of accurately measuring the voltage of a flying capacitor without being affected by the deviation of the on-time of two semiconductor switches that are turned on or the influence of a common mode voltage when measuring the voltage of the flying capacitor. Is to provide.

The invention of claim 1 includes a sensor, a first semiconductor switch connected to one output terminal of the sensor, a second semiconductor switch connected to the first semiconductor switch, and the other output terminal of the sensor. Between the connected third semiconductor switch, the fourth semiconductor switch connected to the third semiconductor switch, and the connection intermediate point of the first and second semiconductor switches and the connection intermediate point of the third and fourth semiconductor switches And a first and second flying capacitors connected in series and connected in series,
A connection intermediate point of the first and second flying capacitors is grounded via a fifth semiconductor switch;
A differential voltage detection circuit for detecting a difference between an output voltage of the second semiconductor switch and an output voltage of the fourth semiconductor switch ;
A non-inverting input terminal and an inverting input terminal of the differential voltage detection circuit are grounded via a sixth semiconductor switch .

According to a second aspect of the present invention, there is provided a sensor, a first semiconductor switch connected to one output terminal of the sensor, a second semiconductor switch connected to the first semiconductor switch, and the other output terminal of the sensor. Between the connected third semiconductor switch, the fourth semiconductor switch connected to the third semiconductor switch, and the connection intermediate point of the first and second semiconductor switches and the connection intermediate point of the third and fourth semiconductor switches And a plurality of combinations with the first and second flying capacitors connected in series,
The connection midpoint of each of the first and second flying capacitors is grounded via the fifth semiconductor switch,
One differential voltage detection circuit for detecting the difference between the output voltage of each second semiconductor switch and the output voltage of each fourth semiconductor switch ;
The differential voltage detection circuit is characterized in that the non-inverting input terminal and the inverting input terminal are grounded via a sixth semiconductor switch .

  According to the present invention, accurate measurement can be performed even if there is a deviation in the on-time of the two semiconductor switches that are turned on when measuring the voltage of the flying capacitor. In addition, the flying capacitor voltage can be accurately measured without being affected by the common mode voltage.

  Hereinafter, an embodiment of a multi-point temperature measuring device which is one of measuring devices according to the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of the multipoint temperature measuring apparatus 10. The multi-point temperature measuring apparatus 10 includes a plurality of measurement circuits 11A, 11B... That measure the temperature at each measurement point, and a differential voltage detection circuit 12 that detects a difference between voltages output from the measurement circuits 11A, 11B. A semiconductor switch (sixth semiconductor switch) 13, an A / D converter 14 for A / D converting the output voltage output from the differential voltage detection circuit 12, and a digital signal output from the A / D converter 14. And a measurement control unit 20 that calculates the temperature of each measurement point based on the above.

  The measurement circuit 11A includes a thermocouple (sensor) TU1 that detects a temperature at a predetermined measurement point, a semiconductor switch (first semiconductor switch) SW1 connected to one terminal of the thermocouple TU1, and a semiconductor switch SW1. A semiconductor switch (second semiconductor switch) SW2 connected in series, a semiconductor switch (third semiconductor switch) SW3 connected to the other terminal of the thermocouple TU1, and a semiconductor switch (first semiconductor switch connected in series) to the semiconductor switch SW3 4 semiconductor switch) SW4, flying capacitors (first and second flying capacitors) CF1 and CF2 connected in series, and a semiconductor switch SW5 connected to a connection intermediate point of the flying capacitors CF1 and CF2.

  The first and second flying capacitors CF1 and CF2 connected in series are connected between the connection intermediate point of the semiconductor switches SW1 and SW2 and the connection intermediate point of the semiconductor switches SW3 and SW4, and the semiconductor switch SW5 is grounded. The intermediate connection point of the flying capacitors CF1 and CF2 is grounded through the semiconductor switch SW5. Further, the first and second flying capacitors CF1 and CF2 have the same capacitance.

  Further, a line L1 connecting the semiconductor switch SW2 and the input terminal (non-inverting input terminal) 12a of the differential voltage detection circuit 12, and an input terminal (inverting input terminal) 12b of the semiconductor switch SW4 and the differential voltage detection circuit 12 Is connected to the ground via the semiconductor switch 13.

  The measurement control unit 20 is composed of a CPU or the like, and controls on / off of each semiconductor switch SW1 to SW5, 13 and each semiconductor switch of the measurement circuit B.

  Since the measurement circuit B has the same configuration as the measurement circuit A, the description thereof is omitted.

The semiconductor switches SW1, SW3, SW1 ′, SW3 ′,... May be configured by one multiplexer, and the semiconductor switches SW2, SW4, SW5, SW2 ′, SW4 ′, SW5 ′,.
[Operation]
Next, the operation of the multipoint temperature measuring apparatus 10 configured as described above will be described with reference to the time chart shown in FIG.

  First, under the control of the measurement control unit 20, the semiconductor switches SW1 and SW3 and the semiconductor switch 13 of the measurement circuit 11A are turned on, and the semiconductor switches SW2 and SW4 are turned off (time point t1).

  When the semiconductor switches SW1 and SW3 are turned on, the measurement voltage Vn is charged across the flying capacitors CF1 and CF2. At the same time, the stray capacitances Cf2, Cf4, Cf5 of the semiconductor switches SW2, SW4, SW5 are charged by the common mode voltage Vc.

  The charges charged in the stray capacitances Cf2 and Cf4 have the same amount for the common mode voltage Vc because the stray capacitances Cf2 and Cf4 are equal. The stray capacitance Cf2 is also charged with the measurement voltage Vn.

  Next, when the semiconductor switches SW1, SW3, and 13 are turned off (time t2) and the sampling is completed, the respective charge amounts charged up to the end time are held in the flying capacitors CF1 and CF2 and the stray capacitances Cf2, Cf4, and Cf5. Is done.

  Then, the semiconductor switch SW5 is turned on (time point t3). When the semiconductor switch SW5 is turned on, the charges charged in the stray capacitances Cf2 and Cf4 are discharged and charged in the flying capacitors CF1 and CF2.

  The discharge of the stray capacitances Cf2 and Cf4 is simultaneously performed in the directions indicated by the arrows P1 and P2, and the stray capacitances Cf2 and Cf4 are equal to each other, so that the influence of the common mode voltage Vc on the measurement voltage Vn is offset. Become.

  After the semiconductor switch SW5 is turned on (time point t4), the semiconductor switches SW2 and SW4 are turned on. By turning on the semiconductor switches SW2 and SW4, the voltages Va and Vb of the flying capacitors CF1 and CF2 are input to the input terminals 12a and 12b of the differential voltage detection circuit 12, respectively. The differential voltage detection circuit 12 outputs a voltage corresponding to the difference between the input voltages at the input terminals 12a and 12b.

  Even if the time when the semiconductor switches SW2 and SW4 are turned on is deviated, the influence of the common mode voltage Vc on the measured voltage Vn is canceled by the turning on of the semiconductor switch SW5. Is not affected by the common mode voltage Vc.

  The differential voltage detection circuit 12 outputs a voltage corresponding to the voltage difference Va−Vb with reference to the midpoint of connection of the flying capacitors CF1 and CF2. That is, an output voltage Vj corresponding to the measured voltage Vn is output from the differential voltage detection circuit 12, and this output voltage Vj is not affected by the common mode voltage Vc.

  The A / D converter 14 converts the output voltage Vj into a digital quantity Dj, and the measurement control unit 20 calculates the temperature of the measurement point measured by the thermocouple TU1 based on the digital quantity Dj.

  When the semiconductor switch SW5 is turned on, if the amount of charge stored in the stray capacitance Cf4 on the flying capacitor CF2 is ΔVc, the amount of charge stored in the stray capacitance Cf2 on the flying capacitor CF1 is ΔVc + ΔVn. As described above, the influence of the common mode voltage on the measurement voltage Vn is canceled out.

  The influence of Vn is Cf2 / CF1 = 1/400000 (CF1, CF2 = 2 μF, Cf1, Cf2 = 5 pF), and the voltage (Va−Vb = Vf) of the flying capacitors CF1, CF2 is Vf = Vn (1 + 1/400000). ) This value Vf is proportional to Vn. Since 1 >> 1/400000, the value of Vn / 400000 does not appear as a digital value during AD conversion. That is, gain correction is performed during AD conversion.

  In addition, after the semiconductor switch SW5 is turned on, the magnitude of the influence of the common mode voltage Vc on the flying capacitors CF1 and CF2 is determined from the thermocouple TU1 based on the connection midpoint of the flying capacitors CF1 and CF2. Since the two circuits up to the connection midpoint have the same circuit configuration, the voltage values have the same magnitude. Therefore, the influence of the common mode voltage Vc is removed by the differential voltage detection circuit 12.

  As described above, it is possible to accurately measure the voltage of the flying capacitor without being affected by the common mode voltage due to the deviation of the on-time of the semiconductor switches SW2 and SW4. Further, since the semiconductor switch SW5 is on when the semiconductor switches SW2 and SW4 are on, the differential voltage detection circuit 12 removes the influence of the common mode voltage Vc. For this reason, it is possible to accurately measure the voltage of the flying capacitor.

  When measuring the multipoint temperature, the semiconductor switches SW1 ', SW3' of each measurement circuit 11B ... are turned on simultaneously with the turning on of the semiconductor switches SW1, SW3 of the measurement circuit 11A, and the semiconductor switches SW1, SW3 of the measurement circuit 11A are turned on. Simultaneously with the turn-off, the semiconductor switches SW1 ′, SW3 ′ of the measurement circuits 11B.

  Thereafter, after the measurement of the measurement circuit 11A is completed, that is, after the semiconductor switches SW2, SW4, and SW5 of the measurement circuit 11A are turned off (time point t5), the semiconductor switches SW2, SW4, and SW5 of the measurement circuit 11A are turned on. The semiconductor switches SW2 ′, SW4 ′, and SW5 ′ of the measurement circuit 11B are turned on, and the calculation control unit 12 calculates the temperature of the measurement point measured by the thermocouple TU2 of the measurement circuit 11B.

  When the temperature at the measurement point measured by the measurement circuit 11B is obtained, the temperature at each measurement point is obtained in the same manner as described above.

  In the above embodiment, the multi-point temperature measuring device has been described. However, a temperature measuring device that measures temperature at one point may be used, or a measuring device that measures other than temperature may be used.

It is the circuit diagram which showed the structure of the multipoint temperature measuring apparatus which concerns on this invention. It is the time chart which showed the operation | movement of the multipoint temperature measuring apparatus of FIG. It is the circuit diagram which showed the structure of the conventional multipoint temperature measuring apparatus.

Explanation of symbols

10 Multi-point temperature measuring device 12 Differential voltage detection circuit TU1 Thermocouple (sensor)
TU2 thermocouple (sensor)
SW1 Semiconductor switch SW2 Semiconductor switch SW3 Semiconductor switch SW4 Semiconductor switch SW5 Semiconductor switch CF1 Flying capacitor CF2 Flying capacitor

Claims (3)

A sensor, a first semiconductor switch connected to one output terminal of the sensor, a second semiconductor switch connected to the first semiconductor switch, and a third semiconductor switch connected to the other output terminal of the sensor And a fourth semiconductor switch connected to the third semiconductor switch, and a series connection between a connection intermediate point of the first and second semiconductor switches and a connection intermediate point of the third and fourth semiconductor switches. A measuring device comprising first and second flying capacitors,
A connection intermediate point of the first and second flying capacitors is grounded via a fifth semiconductor switch;
A differential voltage detection circuit for detecting a difference between an output voltage of the second semiconductor switch and an output voltage of the fourth semiconductor switch ;
A non-inverting input terminal and an inverting input terminal of the differential voltage detection circuit are grounded via a sixth semiconductor switch . A sensor, a first semiconductor switch connected to one output terminal of the sensor, a second semiconductor switch connected to the first semiconductor switch, and a third semiconductor switch connected to the other output terminal of the sensor And a fourth semiconductor switch connected to the third semiconductor switch, and a series connection between a connection middle point of the first and second semiconductor switches and a connection middle point of the third and fourth semiconductor switches. A measuring device having a plurality of combinations with the first and second flying capacitors,
The connection midpoint of each of the first and second flying capacitors is grounded via the fifth semiconductor switch,
One differential voltage detection circuit for detecting the difference between the output voltage of each second semiconductor switch and the output voltage of each fourth semiconductor switch ;
A non-inverting input terminal and an inverting input terminal of the differential voltage detection circuit are grounded via a sixth semiconductor switch .   The measuring device according to claim 1, wherein the sensor is a thermocouple.

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