CN108180939B - Multifunctional data acquisition card and measuring method - Google Patents
Multifunctional data acquisition card and measuring method Download PDFInfo
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- CN108180939B CN108180939B CN201711426063.3A CN201711426063A CN108180939B CN 108180939 B CN108180939 B CN 108180939B CN 201711426063 A CN201711426063 A CN 201711426063A CN 108180939 B CN108180939 B CN 108180939B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention belongs to the field of data acquisition, and particularly relates to a multifunctional data acquisition card and a measurement method. The multifunctional data acquisition card provided by the invention comprises: the device comprises a communication interface circuit (1), a microcontroller (2), an analog-to-digital converter (3), a programmable amplifier (4), a measurement type switching module (5) and an input selection relay module (6). The multifunctional data acquisition card provided by the invention can complete the functions of voltage, current, thermal resistance, thermocouple, resistance bridge type pressure sensor signal and other types of data acquisition by switching the electronic switch, and is provided with the microcontroller for carrying out logic control on the multifunctional data acquisition card, so that various types of data acquisition can be realized on a single data acquisition card, the number of devices applied by a related measurement system is reduced, and the cost is reduced. The data acquisition card is provided with the relay for selecting whether the currently accessed measurement signal is a signal to be measured or a calibration signal, so that the on-line calibration function is realized.
Description
Technical Field
The invention belongs to the field of data acquisition, and particularly relates to a multifunctional data acquisition card and a measurement method.
Background
The data acquisition card is used for acquiring various types of data, and the data acquisition card is more and more widely applied in various fields along with the rapid development of modern equipment in the directions of digitalization, informatization and the like.
Most of common data acquisition cards can only acquire one type of data, and when the types of data such as voltage, current, thermal resistance, thermocouple, resistance bridge type pressure sensor signals and the like need to be acquired, various types of different data acquisition cards are required to be equipped, so that the cost and the complexity of the system are increased. Therefore, a multifunctional data acquisition card capable of independently performing the above-mentioned signal acquisition is needed.
Disclosure of Invention
In order to solve the defect that most of the existing data acquisition cards can only acquire one or a few types of data, the invention provides an acquisition card and a measurement method for acquiring data such as voltage, current, thermal resistance, thermocouple, resistance bridge type pressure sensor signals and the like by using a single hardware resource, thereby reducing the test cost.
The invention provides a multifunctional data acquisition card and a measurement method, which are used for acquiring data such as voltage, current, thermal resistance, thermocouple, resistance bridge type pressure sensor signals and the like by using a single hardware resource and reducing the cost.
Technical scheme
The multifunctional data acquisition card provided by the invention comprises: the device comprises a communication interface circuit (1), a microcontroller (2), an analog-to-digital converter (3), a programmable amplifier (4), a measurement type switching module (5) and an input selection relay module (6).
The communication interface circuit (1) comprises an isolation circuit (11) and a level conversion circuit (12), and the communication interface circuit (1) is connected with a digital communication interface of the microcontroller (2).
The general digital output pin of the microcontroller (2) is connected with the control ends of the programmable amplifier (4), the measurement type switching module (5) and the input selection relay module (6), the serial peripheral interface SPI of the microcontroller (2) is connected with the digital interface of the analog-to-digital converter (3), in addition, the microcontroller (2) is also connected with the communication interface circuit (1), and signals are transmitted in two directions.
The input end of the analog-to-digital converter (3) is connected with the output end of the programmable amplifier (4), and the digital interface of the analog-to-digital converter (3) is connected with the SPI interface of the microcontroller (2).
The input end of the programmable amplifier (4) is connected with the output end of the measurement type switching module (5), the output end of the programmable amplifier (4) is connected with the input end of the analog-to-digital converter (3), and the control end of the programmable amplifier (4) is connected with a universal digital output pin of the microcontroller (2).
The measuring type switching module (5) is composed of two 8-channel electronic switches (51) and (52), the input end of the measuring type switching module (5) is connected with the output end of the input selection relay module (6), the output end of the measuring type switching module (5) is connected with the input end of the programmable amplifier (4), and the control end of the measuring type switching module (5) is connected with the SPI (serial peripheral interface) of the microcontroller (2).
The input end of the input selection relay module (6) is respectively connected with an external signal to be measured and a calibration signal, the output end of the input selection relay module (6) is connected with the input end of the measurement type switching module (5), and the control end of the input selection relay module (6) is connected with a universal digital output pin of the microcontroller (2).
Furthermore, the Relay module (6) is composed of three double-pole double-throw relays and a driving circuit, and the Relay1 and the Relay6 are linked to share one double-pole double-throw Relay. The normally closed end of Relay1 is excited by current, and the normally open end is excited by voltage; the normally closed end of Relay6 is floating and the normally open end is grounded. The relays Relay2, Relay3, Relay4 and Relay5 are linked, two double-pole double-throw relays can be adopted, the normally closed end of the Relay is connected with the acquisition end, and the normally open end of the Relay is connected with the calibration end.
A measurement method of a multifunctional data acquisition card comprises the following steps: comprises the following steps;
A. when measuring the voltage, the measurement is carried out according to the following steps:
1. the positive electrode and the negative electrode of the voltage signal are respectively connected to the pins 2# and 3# of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. the electronic switches K7, K8, K11 are closed, the other switches are open, wherein the branch of the switch K11 provides a bias loop;
4. at this time, the voltage of the maximum ± 10V input from the outside can enter the programmable amplifier (PGA) through the measurement type switching module and be attenuated to the range measurable by the analog-to-digital converter through the PGA, thereby completing the measurement.
B. When measuring the current, if the external current signal has a negative pole, the measurement is carried out according to the following steps:
1. the positive electrode and the negative electrode of the current signal are respectively connected to the pins 2# and 3# of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. electronic switches K12, K13, K14, K15 are closed, and other switches are open;
4. at the moment, the current flows in from the signal positive end, flows out from the signal negative end after sequentially passing through Relay3, K12, resistors R2, K14 and Relay4, and the voltage formed by the current flowing through the sampling resistor R2 reaches the input end of the analog-to-digital converter through the switches K13 and K15, so that the measurement is completed.
If the external current signal has no negative pole, the measurement is carried out according to the following steps:
1. the positive pole of the current signal is connected to the No. 2 pin of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. switches K12, K13, K14, K15, K16 are closed, and the other switches are open;
4. at this time, the current flows from the signal positive terminal, passes through Relay3, switch K12 and resistor R2, then flows into the ground loop through switch K16, the voltage formed by the current flowing through sampling resistor R2 reaches the input end of the analog-to-digital converter through switches K13 and K15, and the measurement is completed.
C. When measuring the three-wire system thermal resistance, the measurement is carried out according to the following steps:
1. the two ends of the thermal resistor are respectively connected to the pin # 2 and the pin # 3 of the connector J2, and the pin # 4 of the connector J2 is commonly terminated;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. the electronic switches K4, K5, K6 are closed, and the other switches are open;
4. opening two paths of matched mirror image excitation currents I1 and I2;
5. at this time, currents I1 and I2 respectively flow from pin # 2 and pin # 3 of the connector J2 through the thermal resistor to be tested, and flow from pin # 4 of the connector J2 through the switch K6, through the reference resistor R1, and then flow into the ground loop. The voltage signal on the thermal resistor enters the input end of the analog-digital converter through K4 and K5. The switch K6 provides a bias loop for the exciting current and forms a voltage drop on the resistor R1 as a reference voltage of the analog-to-digital converter, and the measurement of the thermal resistor is completed by adopting a proportional method.
D. When measuring the four-wire heating resistance, the following steps are carried out:
1. the thermal resistors are respectively connected to pins 1#, 2#, 3# and 4# of the connector J2;
2. the relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end;
3. the electronic switches K4, K5 and K6 are closed, the other switches are open;
4. the excitation currents I1 and I2 are closed, and the excitation current I3 is opened;
5. at the moment, the current I3 passes through the Relay1, Relay2, the thermal resistor, Relay5, K6 and the resistor R1 in sequence, and finally flows into a ground loop. The voltage signal on the thermal resistor enters the input end of the analog-digital converter through K4 and K5. The switch K6 provides a bias loop for the exciting current and forms a voltage drop on the resistor R1 as a reference voltage of the analog-to-digital converter, and the measurement of the thermal resistor is completed by adopting a proportional method.
E. When measuring the thermocouple, the following steps are carried out:
1. two ends of the thermocouple are respectively connected to pins 2# and 3# of the connector J2, two ends of the cold-end thermal resistor are respectively connected to pins 1# and 2# of the connector J1, and the common end of the cold-end thermal resistor is connected to a pin 3# of the connector J1;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. electronic switches K4 and K5 are closed, other switches are opened, exciting currents I1 and I2 are closed, and the output value of the thermocouple is measured;
4. electronic switches K1, K2 and K3 are closed, other switches are opened, excitation currents I1 and I2 are opened, the measuring method is consistent with the C three-wire system thermal resistance measuring method, and the temperature of the cold end is measured;
5. and (4) performing cold end compensation calculation by using a microcontroller to complete the measurement of the thermocouple.
F. When measuring the resistance bridge sensor signal, the following steps are performed:
1. the excitation positive terminal of the sensor is connected with the 1# pin of the connector J2, the excitation negative terminal is connected with the 4# pin of the connector J2, the signal positive terminal is connected with the 2# pin of the connector J2, and the signal negative terminal is connected with the 1# pin of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, Relay1 is connected with voltage excitation end V, and Relay6 is connected with the ground end;
3. switches K7 and K8 are closed, the other switches are open;
4. at this time, the output signal of the sensor can enter a programmable amplifier to be amplified to a range which can be measured by an analog-to-digital converter after passing through electronic switches K7 and K8, and the measurement is finished.
G. When on-line calibration is carried out, the relays Relay2, Relay3, Relay4 and Relay5 are connected with the calibration end, the standard signal is introduced from the calibration end, and the on-off states of other switches are consistent with the items A-F.
The invention has the advantages that: the multifunctional data acquisition card provided by the invention can complete the functions of voltage, current, thermal resistance, thermocouple, resistance bridge type pressure sensor signal and other types of data acquisition by switching the electronic switch, and is provided with the microcontroller for carrying out logic control on the multifunctional data acquisition card, so that various types of data acquisition can be realized on a single data acquisition card, the number of devices applied by a related measurement system is reduced, and the cost is reduced.
In addition, the data acquisition card is provided with a relay for selecting whether the currently accessed measurement signal is a signal to be measured or a calibration signal, so that the on-line calibration function is realized.
Elucidation of the advantages and effects
The invention has the advantages that: the multifunctional data acquisition card provided by the invention can complete the functions of voltage, current, thermal resistance, thermocouple, resistance bridge type pressure sensor signal and other types of data acquisition by switching the electronic switch, and is provided with the microcontroller for carrying out logic control on the multifunctional data acquisition card, so that various types of data acquisition can be realized on a single data acquisition card, the number of devices applied by a related measurement system is reduced, and the cost is reduced.
In addition, the data acquisition card is provided with a relay for selecting whether the currently accessed measurement signal is a signal to be measured or a calibration signal, so that the on-line calibration function is realized.
Drawings
FIG. 1 is a block diagram of the multifunctional data acquisition card according to the present invention.
FIG. 2 is a schematic block diagram of a multifunctional data acquisition and measurement method according to the present invention.
Fig. 3 is a pin layout diagram of the analog-to-digital converter according to the present invention.
Detailed Description
As shown in fig. 1, the multifunctional data acquisition card provided by the present invention comprises: the device comprises a communication interface circuit (1), a microcontroller (2), an analog-to-digital converter (3), a programmable amplifier (4), a measurement type switching module (5) and an input selection relay module (6). The communication interface circuit (1) comprises an isolation circuit (11) and a level conversion circuit (12), and the communication interface circuit (1) is connected with a digital communication interface of the microcontroller (2).
The general digital output pin of the microcontroller (2) is connected with the control ends of the programmable amplifier (4), the measurement type switching module (5) and the input selection relay module (6), the serial peripheral interface SPI of the microcontroller (2) is connected with the digital interface of the analog-to-digital converter (3), in addition, the microcontroller (2) is also connected with the communication interface circuit (1), and signals are transmitted in two directions.
The input end of the analog-to-digital converter (3) is connected with the output end of the programmable amplifier (4), and the digital interface of the analog-to-digital converter (3) is connected with the SPI interface of the microcontroller (2).
The input end of the programmable amplifier (4) is connected with the output end of the measurement type switching module (5), the output end of the programmable amplifier (4) is connected with the input end of the analog-to-digital converter (3), and the control end of the programmable amplifier (4) is connected with a universal digital output pin of the microcontroller (2).
The measuring type switching module (5) is composed of two 8-channel electronic switches (51) and (52), the input end of the measuring type switching module (5) is connected with the output end of the input selection relay module (6), the output end of the measuring type switching module (5) is connected with the input end of the programmable amplifier (4), and the control end of the measuring type switching module (5) is connected with the SPI (serial peripheral interface) of the microcontroller (2).
The input end of the input selection relay module (6) is respectively connected with an external signal to be measured and a calibration signal, the output end of the input selection relay module (6) is connected with the input end of the measurement type switching module (5), and the control end of the input selection relay module (6) is connected with a universal digital output pin of the microcontroller (2).
Preferably, the relays Relay2, Relay3, Relay4 and Relay5 are linked, two double-pole double-throw relays can be adopted, the normally closed end of the Relay is connected with the acquisition end, and the normally open end of the Relay is connected with the calibration end. The relays Relay1 and Relay6 use a double-pole double-throw Relay, the normally closed end of Relay1 is connected with current excitation, and the normally open end is connected with voltage excitation; the normally closed end of Relay6 is floating and the normally open end is grounded. Preferably, the analog-to-digital converter (ADC) has 4 pairs of differential voltage input terminals AIN 0-AIN 7, a set of constant current sources (31) and is arbitrarily distributed to the 4 pairs of input terminals and a pair of dedicated current excitation output terminals IOUT1 and IOUT2, and the reference power source can be selected from an internal reference source or an external reference source (voltage between pins REFP0 and REFN 0).
Preferably, the thermocouple and thermistor signal measurement selects pins AIN0 and AIN1 of the ADC, the voltage and resistor bridge sensor signal measurement selects pins AIN2 and AIN3 of the ADC, the current signal measurement selects pins AIN4 and AIN5 of the ADC, the mirror constant current sources I1 and I2 select pins IOUT1 and IOUT2 of the ADC, and the constant current source I3 selects pin AIN6 of the ADC. Preferably, the programmable amplifier has an amplification factor of 1/8-128 times, can reduce a differential voltage signal of +/-10V to a switchable differential voltage range (± 2.048V) of the analog-to-digital converter, and provides a proper common-mode voltage.
The measuring method of the invention utilizes the multifunctional data acquisition card and comprises the following aspects:
A. when measuring the voltage, the measurement is carried out according to the following steps:
1. the positive electrode and the negative electrode of the voltage signal are respectively connected to the pins 2# and 3# of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. the electronic switches K7, K8, K11 are closed, the other switches are open, wherein the branch of the switch K11 provides a bias loop;
4. at this time, the voltage of the maximum ± 10V input from the outside can enter the programmable amplifier (PGA) through the measurement type switching module and be attenuated to the range measurable by the analog-to-digital converter through the PGA, thereby completing the measurement.
B. When measuring the current, if the external current signal has a negative pole, the measurement is carried out according to the following steps:
1. the positive electrode and the negative electrode of the current signal are respectively connected to the pins 2# and 3# of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. electronic switches K12, K13, K14, K15 are closed, and other switches are open;
4. at the moment, the current flows in from the signal positive end, flows out from the signal negative end after sequentially passing through Relay3, K12, resistors R2, K14 and Relay4, and the voltage formed by the current flowing through the sampling resistor R2 reaches the input end of the analog-to-digital converter through the switches K13 and K15, so that the measurement is completed.
If the external current signal has no negative pole, the measurement is carried out according to the following steps:
1. the positive pole of the current signal is connected to the No. 2 pin of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. switches K12, K13, K14, K15, K16 are closed, and the other switches are open;
4. at this time, the current flows from the signal positive terminal, passes through Relay3, switch K12 and resistor R2, then flows into the ground loop through switch K16, the voltage formed by the current flowing through sampling resistor R2 reaches the input end of the analog-to-digital converter through switches K13 and K15, and the measurement is completed.
C. When measuring the three-wire system thermal resistance, the measurement is carried out according to the following steps:
1. the two ends of the thermal resistor are respectively connected to the pin # 2 and the pin # 3 of the connector J2, and the pin # 4 of the connector J2 is commonly terminated;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. the electronic switches K4, K5, K6 are closed, and the other switches are open;
4. opening two paths of matched mirror image excitation currents I1 and I2;
5. at this time, currents I1 and I2 respectively flow from pin # 2 and pin # 3 of the connector J2 through the thermal resistor to be tested, and flow from pin # 4 of the connector J2 through the switch K6, through the reference resistor R1, and then flow into the ground loop. The voltage signal on the thermal resistor enters the input end of the analog-digital converter through K4 and K5. The switch K6 provides a bias loop for the exciting current and forms a voltage drop on the resistor R1 as a reference voltage of the analog-to-digital converter, and the measurement of the thermal resistor is completed by adopting a proportional method.
D. When measuring the four-wire heating resistance, the following steps are carried out:
1. the thermal resistors are respectively connected to pins 1#, 2#, 3# and 4# of the connector J2;
2. the relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end;
3. the electronic switches K4, K5 and K6 are closed, the other switches are open;
4. the excitation currents I1 and I2 are closed, and the excitation current I3 is opened;
5. at the moment, the current I3 passes through the Relay1, Relay2, the thermal resistor, Relay5, K6 and the resistor R1 in sequence, and finally flows into a ground loop. The voltage signal on the thermal resistor enters the input end of the analog-digital converter through K4 and K5. The switch K6 provides a bias loop for the exciting current and forms a voltage drop on the resistor R1 as a reference voltage of the analog-to-digital converter, and the measurement of the thermal resistor is completed by adopting a proportional method.
E. When measuring the thermocouple, the following steps are carried out:
1. two ends of the thermocouple are respectively connected to pins 2# and 3# of the connector J2, two ends of the cold-end thermal resistor are respectively connected to pins 1# and 2# of the connector J1, and the common end of the cold-end thermal resistor is connected to a pin 3# of the connector J1;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. electronic switches K4 and K5 are closed, other switches are opened, exciting currents I1 and I2 are closed, and the output value of the thermocouple is measured;
4. electronic switches K1, K2 and K3 are closed, other switches are opened, excitation currents I1 and I2 are opened, the measuring method is consistent with the C three-wire system thermal resistance measuring method, and the temperature of the cold end is measured;
6. and (4) performing cold end compensation calculation by using a microcontroller to complete the measurement of the thermocouple.
F. When measuring the resistance bridge sensor signal, the following steps are performed:
1. the excitation positive terminal of the sensor is connected with the 1# pin of the connector J2, the excitation negative terminal is connected with the 4# pin of the connector J2, the signal positive terminal is connected with the 2# pin of the connector J2, and the signal negative terminal is connected with the 1# pin of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, Relay1 is connected with voltage excitation end V, and Relay6 is connected with the ground end;
3. switches K7 and K8 are closed, the other switches are open;
4. at this time, the output signal of the sensor can enter a programmable amplifier to be amplified to a range which can be measured by an analog-to-digital converter after passing through electronic switches K7 and K8, and the measurement is finished.
G. When on-line calibration is carried out, the relays Relay2, Relay3, Relay4 and Relay5 are connected with the calibration end, the standard signal is introduced from the calibration end, and the opening and closing of other switches are consistent with the items A-F.
Claims (2)
1. A multifunctional data acquisition card is composed of a communication interface circuit (1), a microcontroller (2), an analog-to-digital converter (3), a programmable amplifier (4), a measurement type switching module (5) and an input selection relay module (6);
the communication interface circuit (1) comprises an isolation circuit (11) and a level conversion circuit (12), and the communication interface circuit (1) is connected with a digital communication interface of the microcontroller (2);
a universal digital output pin of the microcontroller (2) is connected with a programmable amplifier (4), a measurement type switching module (5) and a control end of an input selection relay module (6), a Serial Peripheral Interface (SPI) of the microcontroller (2) is connected with a digital interface of the analog-to-digital converter (3), in addition, the microcontroller (2) is also connected with a communication interface circuit (1), and signals are transmitted in two directions;
the input end of the analog-to-digital converter (3) is connected with the output end of the programmable amplifier (4), and the digital interface of the analog-to-digital converter (3) is connected with the serial peripheral interface SPI of the microcontroller (2);
the input end of the programmable amplifier (4) is connected with the output end of the measurement type switching module (5), the output end of the programmable amplifier (4) is connected with the input end of the analog-to-digital converter (3), and the control end of the programmable amplifier (4) is connected with a universal digital output pin of the microcontroller (2);
the input end of the input selection relay module (6) is respectively connected with an external signal to be measured and a calibration signal, the output end of the input selection relay module (6) is connected with the input end of the measurement type switching module (5), and the control end of the input selection relay module (6) is connected with a universal digital output pin of the microcontroller (2);
the measurement type switching module (5) consists of two 8-channel electronic switches (51) and (52), the input end of the measurement type switching module (5) is connected with the output end of the input selection relay module (6), the output end of the measurement type switching module (5) is connected with the input end of the programmable amplifier (4), and the control end of the measurement type switching module (5) is connected with a universal digital output pin of the microcontroller (2);
the Relay module (6) consists of three double-pole double-throw relays and a driving circuit, and the relays Relay1 and Relay6 are linked to share one double-pole double-throw Relay; the normally closed end of Relay1 is excited by current, and the normally open end is excited by voltage; the normally closed end of Relay6 is suspended, and the normally open end is grounded; the Relay Relay2, Relay3, Relay4 and Relay5 are linked, two double-pole double-throw relays are adopted, the normally closed end of the Relay is connected with the acquisition end, and the normally open end of the Relay is connected with the calibration end;
the measuring method of the multifunctional data acquisition card is characterized by comprising the following steps:
A. when measuring the voltage, the measurement is carried out according to the following steps:
1. the positive electrode and the negative electrode of the voltage signal are respectively connected to the pins 2# and 3# of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. the electronic switches K7, K8, K11 are closed, the other switches are open, wherein the branch of the switch K11 provides a bias loop;
4. at the moment, the voltage with the maximum +/-10V of the external input can enter the programmable amplifier through the measurement type switching module, and is attenuated to the range which can be measured by the analog-to-digital converter through the programmable amplifier to finish the measurement;
B. when measuring the current, if the external current signal has a negative pole, the measurement is carried out according to the following steps:
1. the positive electrode and the negative electrode of the current signal are respectively connected to the pins 2# and 3# of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. electronic switches K12, K13, K14, K15 are closed, and other switches are open;
4. at the moment, current flows in from the signal positive end, flows out from the signal negative end after sequentially passing through Relay3, K12, sampling resistors R2, K14 and Relay4, and voltage formed by the current flowing through the sampling resistor R2 reaches the input end of the analog-to-digital converter through switches K13 and K15 to finish measurement;
if the external current signal has no negative pole, the measurement is carried out according to the following steps:
1. the positive pole of the current signal is connected to the No. 2 pin of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. switches K12, K13, K14, K15, K16 are closed, and the other switches are open;
4. at the moment, current flows from the signal positive terminal, flows into a ground loop through the Relay3, the switch K12 and the sampling resistor R2 and then flows into the ground loop through the switch K16, and voltage formed by the current flowing through the sampling resistor R2 reaches the input end of the analog-to-digital converter through the switches K13 and K15 to finish measurement;
C. when measuring the three-wire system thermal resistance, the measurement is carried out according to the following steps:
1. the two ends of the thermal resistor are respectively connected to the pin # 2 and the pin # 3 of the connector J2, and the pin # 4 of the connector J2 is commonly terminated;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. the electronic switches K4, K5, K6 are closed, and the other switches are open;
4. opening two paths of matched mirror image excitation currents I1 and I2;
5. at the moment, currents I1 and I2 respectively flow through the thermal resistor to be tested from the 2# pin and the 3# pin of the connector J2, and flow into a ground loop from the 4# pin of the connector J2 through the switch K6 and the reference resistor R1; voltage signals on the thermal resistor enter the input end of the analog-to-digital converter through K4 and K5; the switch K6 provides a bias loop for the exciting current, forms a voltage drop on the resistor R1 as a reference voltage of the analog-to-digital converter, and adopts a proportional method to complete the measurement of the thermal resistor;
D. when measuring the four-wire heating resistance, the following steps are carried out:
1. the thermal resistors are respectively connected to pins 1#, 2#, 3# and 4# of the connector J2;
2. the relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end;
3. the electronic switches K4, K5 and K6 are closed, the other switches are open;
4. the excitation currents I1 and I2 are closed, and the excitation current I3 is opened;
5. at the moment, the current I3 sequentially passes through the Relay1, the Relay2, the thermal resistor, the Relay5, the K6 and the resistor R1, and finally flows into a ground loop; voltage signals on the thermal resistor enter the input end of the analog-to-digital converter through K4 and K5; the switch K6 provides a bias loop for the exciting current, forms a voltage drop on the resistor R1 as a reference voltage of the analog-to-digital converter, and adopts a proportional method to complete the measurement of the thermal resistor;
E. when measuring the thermocouple, the following steps are carried out:
1. two ends of the thermocouple are respectively connected to pins 2# and 3# of the connector J2, two ends of the cold-end thermal resistor are respectively connected to pins 1# and 2# of the connector J1, and the common end of the cold-end thermal resistor is connected to a pin 3# of the connector J1;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, and Relay1 and Relay6 are connected with the normally closed end;
3. electronic switches K4 and K5 are closed, other switches are opened, exciting currents I1 and I2 are closed, and the output value of the thermocouple is measured;
4. electronic switches K1, K2 and K3 are closed, other switches are opened, excitation currents I1 and I2 are opened, the measuring method is consistent with the C three-wire system thermal resistance measuring method, and the temperature of the cold end is measured;
5. performing cold end compensation calculation by using a microcontroller to complete measurement of the thermocouple;
F. when measuring the resistance bridge sensor signal, the following steps are performed:
1. the excitation positive terminal of the sensor is connected with the 1# pin of the connector J2, the excitation negative terminal is connected with the 4# pin of the connector J2, the signal positive terminal is connected with the 2# pin of the connector J2, and the signal negative terminal is connected with the 3# pin of the connector J2;
2. relays Relay2, Relay3, Relay4 and Relay5 are connected with the acquisition end, Relay1 is connected with voltage excitation end V, and Relay6 is connected with the ground end;
3. switches K7 and K8 are closed, the other switches are open;
4. at this time, the output signal of the sensor can enter a programmable amplifier to be amplified to a range which can be measured by an analog-to-digital converter after passing through electronic switches K7 and K8, and the measurement is finished.
2. The multifunctional data acquisition card according to claim 1, wherein: when the on-line calibration is carried out, only the relays Relay2, Relay3, Relay4 and Relay5 need to be connected with the calibration end, the standard signal is introduced from the calibration end, and the on-off states of other switches are consistent with the items A-F.
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