RU2233453C2 - Multichannel resistance meter - Google Patents

Abstract

FIELD: measuring technique.

SUBSTANCE: each of contacts 1-1, 1-2,…1 -n directly or through respective resistor 2-1,2-2,..2-n and respective resistor 3-1,3-2,..3-n is connected with second outlet of respective controlled switch 4-1, 4-2,..4-n and respective controlled switch 5-1,5-2,..5-n. First inlets of controlled switches 4-1,4-2,..4-n are connected with outlet of controlled direct current source and with first outlet of additional controlled switch whose second outlet is connected with inlet of voltage meter to which potential proportional to circuit resistance is fed. First outlets of controlled switches 5 -1, 5-2,.. 5-n are combined and connected with common bus of meter. Control inlets of controlled switches 4-1, 4-2,..4-n and of controlled switches 5-1, 5-2,.. 5-n are connected with respective outlets of control unit. Control inlet of controlled direct current source is connected with respective outlet of control unit.

EFFECT: enlarged functional possibilities of metering device.

1 dwg

Description

The invention relates to measuring equipment and can be used in systems for remote measurement of resistance of resistive sensors.

A known resistance meter (see USSR author's certificate No. 1283669 of 05/06/85, MKI G 01 R 27/00. Device for remote measurement of resistance, authors S. A. Bekaryuk and V. A. Piskunov, publ. 15.01.87, BI No. 2), containing a resistive sensor, a switch, a controlled current source, a control unit, a voltage converter - code, a computing unit, an indication unit, connecting wires. The switch contains the first managed key and control. A controllable current source comprises first and second current sources and a second controllable key. The first output of the resistive sensor is connected to the first output of the first controlled key and, through a connecting wire, to the first output of the controlled current source and to the first input of the voltage converter, is a code. The second output of the resistive sensor is connected to the second output of the first controlled key, and through a series-connected control element and the second connecting wire, to the second output of the controlled current source and to the second input of the voltage converter is a code. Voltage converter output - the code is connected to the first output of the computing unit, the second input of which is connected to the first output of the control unit, and the output is connected to the display unit. The second output of the control unit is connected to the control input of a controlled current source. The first terminal of the first current source is connected to the first terminal of the second controlled key and to the first output of the controlled current source, the second output of which is connected to the second terminals of the first and second current sources. The first terminal of the second current source is connected to the second terminal of the second controlled key, the control input of which is connected to the control input of the controlled current source.

The disadvantages of the known device are low measurement accuracy in the range of small resistances of resistive sensors and single-channel (the ability to measure the resistance of only one resistive sensor). Low measurement accuracy in the range of low resistances of resistive sensors is associated with the absence of compensation of the resistance of the controlled key connected in parallel with the measured resistive sensor. In the case of using an electronic circuit as a controlled key using semiconductor elements as switches, it is necessary to take into account that the resistance of these elements can be comparable to or even exceed the measured resistance of the resistive sensor, and also has significant values of technological spread and changes in operating conditions. Moreover, unless special measures are taken to compensate for the resistance of the controlled key, the measurement accuracy is low. The use of an electromagnetic relay contact as a controlled key can reduce the influence of the key on the measurement accuracy, however, it sharply reduces the device’s operating life by the number of permissible communications, and also reduces the device’s speed.

The closest set of essential features is a multichannel resistance meter (see USSR author's certificate No. 1697017 of 05.24.89, MKI: G 01 R 27/00, Multichannel resistance meter of resistive sensors, authors L.I. Makeeva, V.D. Shalynin , V.A. Timchenko, published 07.12.91., Bull. No. 45), selected as a prototype and containing n resistive sensors, a switch, a direct current source, voltage meter, differential amplifier, control unit, communication lines, connecting wires , n channels, each of which with holds terminals (contacts) for connecting resistive sensors. The switch contains controlled keys, two for each resistive sensor, with the first terminals of each pair of controlled keys connected via connecting wires to the first terminals of the corresponding resistive sensors, the second terminals of the first controlled keys combined and connected to the first output of the DC source through the first communication line, the second the outputs of the second managed keys are combined and connected through the second communication line to the first input of the meter, the control inputs of each pair of controlled keys are combined are connected to respective outputs of the control unit. The second conclusions of each of the resistive sensors with numbers from the 1st to the (n-1) th through the connecting wires are connected to the second conclusions of the resistive sensors with numbers, respectively, from the 2nd to the n-th. The second output of the first resistive sensor through the third communication line is connected to the inverse input of the differential amplifier. The second output of the nth resistive sensor through the fourth communication line is connected to the output of the differential amplifier. The direct input of the differential amplifier, the second input of the meter and the second output of the DC source are connected to a common bus of the device.

In this resistance meter, the influence of the resistance of the controlled switches on the result of measuring the resistance of the resistive sensors due to the large input resistance of the voltage meter and the greater output resistance of the DC source is excluded. This makes it possible to use electronic circuits as controlled keys using semiconductor elements as switches and thereby remove restrictions on the number of key commutations and increase the speed of the device.

A disadvantage of the known resistance meter is its limited functionality associated, firstly, with the inability to control the isolation between the disconnected circuits of the resistive sensors, since the second conclusions of the disconnected sensors are connected by connecting wires; secondly, with the impossibility of connecting the terminals of resistive sensors to any contacts of the device (for example, you cannot connect a resistive sensor between contacts with even numbers).

The problem solved by the invention is the creation of a multi-channel resistance meter with advanced functionality that allows you to:

- to control the isolation resistance between disconnected circuits of resistive sensors;

- remove restrictions on the connection of resistive sensors to the contacts of the resistance meter.

The technical result, which consists in expanding the functionality, is achieved by the fact that in a multi-channel resistance meter containing a voltage meter, n contacts for connecting resistive sensors, two managed keys for each contact with odd numbers, the first outputs of the first managed keys of each pair are combined and connected to the output of the DC source, the first outputs of the second managed keys of each pair are interconnected, the control inputs of the managed keys are connected to The control unit outputs two additional controlled keys for each contact with even numbers for connecting resistive sensors and an additional controlled third key, the DC source is made in the form of a controlled DC source, the control input of which is connected to the corresponding output of the control unit, each of the contacts with odd numbers connected to the second terminals of the corresponding managed keys directly or through the corresponding first and second resistors, to each of the contacts with even numbers is connected to the second terminals of the corresponding additional managed keys directly or through the corresponding first and second additional resistors, the first terminals of the first additional controlled keys of each pair are connected and connected to the connection point of the first terminals of the first managed keys and to the first terminal of the third additional controlled key, the second output of which is connected to the input of the voltage meter, which receives a potential proportional to rank resistance circuit, a connection point of first terminals managed by the second key and the first terminal of the second additional driven keys of each pair are interconnected and connected to a common bus device, additional control inputs driven keys and third additional controllable switch connected to the respective outputs of the control unit.

The specified set of features allows you to expand the functionality of a multi-channel resistance meter, which allows you to:

- to control the isolation resistance between disconnected circuits of resistive sensors;

- remove restrictions on the connection of resistive sensors to the contacts of the device by eliminating the influence of the input circuits of the multichannel meter on the value of the isolation between the contacts and on the resistance value of the resistive sensors.

The drawing shows a circuit diagram of a multi-channel resistance meter.

The multi-channel resistance meter contains contacts 1-1, 1-2, ... 1-n for connecting resistive sensors, the first resistors 2-1, 2-2, ... 2-n, the second resistors 3-1, 3-2 , ... 3-n, the first managed keys 4-1, 4-2, ... 4-n, the second managed keys 5-1, 5-2, ... 5-n, the third managed key 6, block 7 control, voltage meter 8, a common bus 9, a controlled DC source 10, an electronic computer 11, a fourth controlled key 12 and a fifth controlled key 13, a resistor 14. A controlled source 10 is supplied from a constant source 15 to straining. The controlled direct current source 10 contains the first 16 and second 17 controlled keys, a resistor 18 and a direct current source 19. Each of the contacts 1-1, 1-2, ... 1-n directly or through a resistor 2-1, 2-2, ... 2-n and a resistor 3-1, 3-2, ... 3- n is connected to the second terminal of the corresponding managed key 4-1, 4-2, ... 4-n and the managed key 5-1, 5-2, ... 5-n, the first conclusions of the managed keys 4-1, 4- 2, ... 4-n are combined and connected to the output of the controlled DC source 10 and the first output of the managed key 6, the second output of which is connected to the input of the voltage meter 8, the first conclusions of the controlled keys 5-1, 5-2, ... 5-n are combined and connected to a common bus 9 of the device.

The control inputs of the controlled keys 4-1, 4-2, ... 4-n and controlled keys 5-1, 5-2, ... 5-n are connected to the corresponding terminals of the control unit 7. The control input of the controlled DC source 10 is connected to the corresponding output of the control unit 7. The first output of the controlled key 12 is connected to the output of the controlled current source 10, the second output of which is connected to the first output of the controlled key 13 and through the resistor 14 to the common bus 9 of the device. The second output of the managed key 13 is connected to the input of the voltage meter 8, the output of which is connected to the input of the computer 11. The control inputs of the managed key 12, the managed key 13 and the voltage meter 8 are connected to the corresponding outputs of the control unit 7. The output of the computer 11 is connected to the input of the control unit 7. The input of the controlled direct current source 10 is connected to a constant voltage source 15. The output of the DC source 19 is connected to the first output of the controlled key 17, the second output of which is the output of the controlled DC source 10 and connected to the second output of the controlled key 16, the first output of which is connected through the resistor 18 to the input of the DC source 19, which is the input of the controlled DC source 10. The control inputs of the managed key 16 and the controlled key 17 are combined and are the control input of the controlled DC source 10.

Managed keys 4-1, 4-2, ... 4-n; 5-1, 5-2, ... 5-n; 6; 12; thirteen; 16; 17 can be performed on the chip 564KT3, the inversion of the control signal supplied to the key 16, can be obtained using an inverter.

The control unit 7 can be constructed according to the scheme described in the book "One Hundred Schemes with Indicators", Yu.A. Bystrov, G.M. Persianov. - M .: Radio and communications, 1991, 272 p., Fig. 2.3. Instead of the indicator shown in Fig.2.3, it is necessary to connect the control inputs of a multi-channel resistance meter. The control unit 7 can also be built on the microcontroller H1830BE51 / 31.

The voltage meter 8 can be performed on the chip N572PVZ, which is an ADC. As a voltage meter 8, you can also use a digital voltmeter B7-38.

As a computer 11, you can use the personal computer IBM PC / XT / AT or another electronic device based on a microprocessor.

A direct current source 19 and a constant voltage source 15 can be constructed according to well-known circuits described in the book "The Art of Circuit Engineering", t.1, p. Horvits, W. Hill, ed. 4th. - M .: Mir, 1993, p. fifteen.

Multichannel resistance meter works as follows.

When the power is turned on, the control unit 7 sets on all control inputs of the controlled keys 4-1, 4-2, ... 4-n and the controlled keys 5-1, 5-2, ... 5-n the signals corresponding to the closed state of all the aforementioned managed keys. Managed keys 6, 12, 13 are also closed. Voltage meter 8 is prohibited from taking measurements. This state of the multi-channel meter is hereinafter referred to as the “initial state”. After setting the control program unit 7 to a work program or according to a fixed operation algorithm, the control unit 7 starts to generate signals necessary for measuring the resistance between contacts 1-1, 1-2, ... 1-n. Suppose a resistance is measured between pins 1-1 and 1-n. The control signal control unit 7 opens the controlled key 17, closes the controlled key 16, thereby it connects the direct current source 19 to the output of the controlled direct current source 10. The control signals open one of the pairs of managed keys 4-1, 5-1; 4-n, 5-n; 4-1, 5-n; 4-n, 5-1; as well as a controlled key 6. Current from a controlled DC source 10 through an open pair of keys flows to a common bus 9 of the device. At the input of the voltage meter 8 through the controlled key 6, a potential is proportional to the value of the circuit resistance connected between the output of the controlled DC source 10 and the device common bus 9. The voltage meter 8 must have a high input resistance, then the resistance of the controlled switch 6 will not affect the measurement result. After a temporary pause sufficient for the end of transient processes in the circuits connected to the output of the controlled direct current source 10, the control signal control unit 7 allows the voltage meter 8 to start the measurement. The voltage meter 8 represents the measurement result as a number in binary code. From the output of the voltage meter 8, the measurement result is read into a computer 11, where it is processed and stored. After the measurement result is transmitted to the computer 11, the multichannel resistance meter switches to its original state.

The measurement process is carried out similarly as described above for each open key pair: 4-1, 5-1; 4-n, 5-n; 4-1, 5-n; 4-n, 5-1. The result is four measurement results. Using the four measurement results obtained, the computer 11 calculates the resistance of the resistive sensor. If the number at the output of the voltage meter 8 during the resistance measurement exceeds a certain boundary number, the control unit 7, using the control signal, changes the current generated by the controlled direct current source 10. For this, the controlled key 17 is closed and the key 16 is opened. The control signal control unit 7 opens a pair of controlled keys 4-1, 5-n; either 4-n, 5-1 and the managed key 6. The remaining managed keys are private. One measurement is taken. After the measurement result is transmitted to the computer 11, the multichannel resistance meter switches to its original state. Computer 11 calculates the resistance of the resistive sensor.

Measurement of resistance between other contacts is carried out similarly to the above.

To improve the accuracy of measuring the resistances of resistive sensors and to calculate the conversion coefficient, voltage is the number that is used later in calculating the resistance of a resistive sensor, it is necessary to calibrate the device. For this, a multi-channel resistance meter is set to its initial state. The control signal control unit 7 opens the controlled keys 16 or 17 (depending on which measuring range is calibrated) and the keys 12, 13. Thus, direct current from the controlled direct current source 10 flows through the key 12 and the calibration resistor 14 to a common bus 9 devices. At the calibration resistor 14, the resistance of which is known, a voltage drop is created, which, through the key 13, is fed to the input of the voltage meter 8. From the output of the voltage meter 8, the measurement result is sent to a computer 11, where it is processed and stored for future use in calculating the measured resistances.

When measuring the resistance of resistive sensors, the latter can be connected to the contacts 1-1, 1-2, ... 1-n of the device in an arbitrary order. We show that the resistance of the controlled keys 4-1, 4-2, ... 4-n, 5-1, 5-2, ... 5-n, of the communication wires between contacts 1-1, 1-2, .. . 1-n and the above-mentioned controlled keys, as well as the resistances of the resistors 2-1, 2-2, ... 2-n, 3-1, 3-2, ... 3-n, which can be inserted into the device for protection of resistive sensors from dangerous currents, the appearance of which is possible with a single failure of the device, does not affect the result of measuring the resistance of the resistive sensor. In the calculations below, the resistances of the resistors 2-1, 2-2, ... 2-n, 3-1, 3-2, ... 3-n include the resistances of the above communication wires. Let a resistive sensor with resistance Rx be connected between the contacts 1, n of the device. The measurement is carried out in four stages. At the first stage, the control unit 7 closes the keys 4-1, 5-1, 6, 17; other keys (4-2, ... 4-n, 5-2, ... 5-n, 12, 13, 16) are open. A stable current I ₀ from the source 19 flows through a closed controlled key 17, a key 4-1, resistors 2-1, 3-1, a key 5-1 to a common bus 9. The meter 8 through the public key 6 records the voltage A ₁ , while :

where K ₁ is the conversion coefficient of the meter 8 in the first measurement stage;

R _4-1 + R _5-1 - the resistance of the open managed keys, respectively 4-1 and 5-1;

R _2-1 + R _3-1 - resistance of the resistors, respectively 2-1, 3-1.

At the second measurement stage, the keys 4-n, 5-n, 6, 17 are open; keys 4-1, ... 4- (n-1), 5-1, ... 5- (n-1), 12, 13, 16 are closed. The current from the source 19 flows along the path: switch 17, switch 4-n, 2-n, 3-n switch 5-n, bus 9. Meter 8 detects the voltage A ₂ :

where K ₂ is the conversion coefficient of the meter 8 in the second measurement stage;

R _4-n + R _5-n is the resistance of the public managed keys, respectively 4-n and 5-n;

R _2-n + R _3-n is the resistance of the resistors 2-n and 3-n, respectively.

At the third stage, keys 4-1, 5-n, 6, 17 are open; other keys are private. The meter 8 captures the voltage And ₃ :

where K ₃ is the conversion coefficient of the meter 8 in the third measurement stage;

R _x is the resistance of the resistive sensor.

At the fourth stage, the keys 4-n, 5-1, 6, 17 are open; other keys are private. The meter 8 captures the voltage And ₄ :

where K ₄ is the conversion coefficient of the meter 8 in the fourth stage of measurement.

Add terms (1) and (2) term by term, then equalities (3) and (4), and then subtract the first from the second result. Assuming that the conversion characteristic of meter 8 is constant, since all four measurements occur in a short period of time (millisecond), we take K ₁ = K ₂ = K ₃ = K ₄ = K, we get: A ₃ + A ₄ -A ₂ -A ₁ = K * I ₀ * 2 * R _x . Resistance R _x is found by the formula:

From formula (5) it follows that, knowing the conversion coefficient K and the current value I ₀ , it is possible to calculate the value of the sensor resistance R _x , while the resistance of lines 2-1,3-1, 2-n, 3- n communication, as well as the resistance of the controlled keys 4-1, 5-1, 4-n, 5-n. To improve the measurement accuracy, the value of K * I ₀ can be clarified by calibrating the measurement channel. According to the measurement results of the calibration resistor 14, the product K * I _{0 is} calculated and substituted in the formula (5). When measuring the isolation resistance between disconnected circuits of resistive sensors, the device allows you to control the specified parameter for any pair of contacts 1-1, 1-2, ... 1-n, and when combining these contacts into groups. The result of measuring the isolation resistance is affected by the leakage currents of all public and private controlled keys of the circuit. To reduce the influence on the result of measuring leakage currents, it is necessary that the measuring current is much larger than the leakage currents. When measuring the isolation resistance, the controlled direct current source 10 generates a lower direct current than when measuring the resistance of the resistive sensor. For this, the control signal control unit 7 reconstructs the controlled direct current source 10 as follows: the key 16 is opened, the key 17 is closed, and the output current (I _output ) of the source 10 is described by the formula:

where U ₀ is the voltage of the source 15 of the constant voltage;

R ₁₈ is the resistance of the resistor 18;

R _x is the measured isolation resistance.

The inverse-proportional dependence of the current I _o on resistance R _x allows you to expand the upper limit of the range of measured isolation resistances. The choice of resistor R ₁₈ matches the input voltage range at the input of the meter 8 with its operating range. Since the measured decoupling resistances are much larger in magnitude than the resistances of controlled keys and the resistances of communication lines, the latter do not have a noticeable effect on the measurement result, so the measurement is performed in one step. For example, if it is necessary to measure the isolation resistance between disconnected circuits connected to pins 1-1 and 1-2, it is necessary to close the keys 4-1, 5-2.6 with signals from the control unit 7; open the remaining keys of the circuit. In this case, the current I _output from the source 10 flows through the key 4-1, the communication line 2-1, the resistance R _x , the communication line 3-2, the key 5-2 to the bus 9.

The voltage at the input of the meter (U _o ) 8 is equal to:

Resistance R _x is found by the formula:

To increase the accuracy of the measurement, a measurement channel is calibrated immediately before the measurement. For calibration, calibration resistors of different ratings can be used.

From the above it follows that resistive sensors can be connected between any contacts of the device, and it is also possible to control the isolation resistance between disconnected circuits of resistive sensors. Thus, the functionality of a multi-channel resistance meter is expanded, which allows:

- to control the isolation resistance between disconnected circuits of resistive sensors;

- remove restrictions on the connection of resistive sensors to the contacts of the device.

A laboratory prototype of a multi-channel resistance meter was manufactured, tests of which confirmed the feasibility and practical value of the claimed object.

Claims (1)

A multi-channel resistance meter containing a voltage meter, n contacts for connecting resistive sensors, two controlled keys for each contact with odd numbers, the first outputs of the first managed keys of each pair are combined and connected to the output of a DC source, the first conclusions of the second managed keys of each pair are connected between themselves, the control inputs of the managed keys are connected to the corresponding outputs of the control unit, characterized in that two additional managed keys are entered and each contact with even numbers for connecting resistive sensors and an additional controlled third key, the DC source is made in the form of a controlled DC source, the control input of which is connected to the corresponding output of the control unit, each of the contacts with odd numbers is connected to the second terminals of the corresponding controlled keys directly or through the corresponding first and second resistors, each of the contacts with even numbers is connected to the second conclusions corresponding him additional controlled keys directly or through the corresponding first and second additional resistors, the first conclusions of the first additional controlled keys of each pair are combined and connected to the connection point of the first conclusions of the first managed keys and to the first output of the third additional controlled key, the second output of which is connected to the input of the voltage meter , which receives a potential proportional to the value of the circuit resistance, the connection point of the first terminals of the second controlled switches s and the first terminal of the second additional driven keys of each pair are interconnected and connected to a common bus device, additional control inputs driven keys and third additional controllable switch connected to the respective outputs of the control unit.