RU2343494C1 - Multichannel resistive sensors resistance - voltage converter - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is attributed to technical facilities for measuring non-electrical values using electrical method. Multichannel resistive sensors resistance - voltage converter contains reference voltage source, four sources of weighted voltage, two constant current sources, bidirectional pulse current modulator, current switch through which resistive sensor and its resistive equivalent is fed, voltage-operated outputs of which are connected via voltage switch to differential input of instrumental operating amplifier. Output of instrumental amplifier is connected to input of analog-digital converter connected with microcontroller where control signals for converter are generated, measured signals are processed and digital equivalent of measurement result is formed.

EFFECT: error reduction due to lowering noise from active elements and their parameters stabilisation because of galvanic separation of power supplies and interference resistance increase due to using bidirectional current supply of resistive sensor and its resistive equivalent and using measurement signal processing algorithm in which additive components in measured signal are essentially excluded.

2 dwg

Description

The invention relates to measuring technique, in particular to means for measuring non-electrical quantities by electrical means. It can be used in devices for measuring physical parameters, which use strain gauge and thermistor sensors that change their resistance when the value of the physical parameter is varied. The device allows you to work with various schemes for including resistive sensors, such as single, half-bridge, bridge, "socket", etc.

Known devices for converting resistances to voltages, including resistance sensors, a current generator (source) connected to the sensor whose signal is being processed at a given time, for example:

A.S. USSR No. 865011 "Multichannel measuring device"

IPC G01C 15/00. 1981

A.S. USSR No. 1394162

"Multichannel converter for resistive sensors",

IPC Н02J 9/06. 1986 year

RF patent No. 2031447 "Multichannel measuring device",

IPC G08C 15/00. 1981

RF patent No. 2205413

"Converter of active resistance to direct voltage"

IPC G01R 27/00. 2003 year

RF patent No. 2028630

"Converter changes resistance to voltage",

IPC G01R 27/00. 2003 year

The disadvantages of these devices is the lack of accuracy and noise immunity of the devices.

Closest to the claimed solution is the device described in RF patent No. 2219555 "Multichannel resistance to voltage converter", IPC G01R 27/00. 2003, the Converter contains a current generator, consisting of a power source, a reference voltage source (ION), an op-amp operational amplifier with a limiting and reference resistors (constant current source), a reference resistor (resistive equivalent device R _n ), resistance sensors (resistive sensor R), connecting circuits [current circuits (current bus) and measuring circuits (potential bus)], input protective diodes (current switch), output protective diodes, low-pass filters, capacitor, differential th output i-th channel (potential bus) multiplexed analog-to-digital converter Matzpen consisting: of differential channel multiplexer (voltage switch), normalizing amplifier (tool operational amplifier DUT) and an analog-digital converter), a condenser and lowpass filters.

In the converter, the signals of a large number of resistance sensors are alternately converted to voltage. Resistance sensors are included in the traditional four-wire circuit.

The disadvantage of this device is its low performance due to the installation in the measuring circuit of noise suppressing low-pass filters with a narrow passband of low-frequency signals. The big disadvantage is that all resistance sensors are connected in series along the current flow circuit. The output of the current source is connected to the input circuit of the current flow of the resistive sensor of the first channel, and the output circuit of the current flow of the resistive sensor of the last channel is connected to the negative feedback input of the current generator (circuit most susceptible to emergency). Such a circuitry solution requires the construction of a powerful current source and its high supply voltage, as well as an additional number of diodes to eliminate emergency situations in the external sensor circuits. The noise characteristics of the current source are not clear with a significant number of connected resistive sensors. DC power supply to the measuring circuits reduces conversion accuracy. Also, the DC sensor power supply does not fully meet the issues of combating additive signals that occur in the input circuits of the measuring circuit, for example, thermo-emf.

Any emergency (open circuit in the external sensor connection diagram) leads to a loss of operability of the group of sensors and requires an additional number of built-in diodes (equivalent to building a current switch), which is acceptable for a small group of sensors, for example, for a single 4-component strain gauge socket.

The objective of the invention is to improve the reliability and availability of the device. The technical result is to reduce the error of the device by increasing its noise immunity, speed, low intrinsic noise and stability, complete galvanic isolation from common power sources and ground circuits of the measurement object, as well as the use of bi-directional current supply of resistive sensors and an algorithm for processing measurement results.

The technical result is achieved in that a multichannel converter of resistance of resistive sensors to voltage, containing a common power source, a reference voltage source, a direct current source, resistive sensors and a resistive equivalent device, a current switch, a voltage switch, an instrumental operational amplifier and an analog-to-digital converter, introduced a second DC source, four sources of weighted voltage, the inputs of two of which are connected to a common pi source voltages, and the outputs are connected to the power buses of the operational amplifiers of two direct current sources, and the inputs of two other sources of weighted voltage are connected to the output of the reference voltage source and their outputs are connected to the inputs of two direct current sources, the outputs of the latter are connected to the inputs of the modulator of the pulse bi-directional current, and its outputs are connected to the inputs of the current switch power supply of resistive sensors and a resistive equivalent device, and the potential bus resistive sensors and resistive equivalent devices are connected to a voltage switch, the output of which is connected to the differential input of the instrumental operational amplifier, the output of which is connected to the input of an analog-to-digital converter connected to the microcontroller to form a diagram of the device, receive and execute the algorithm for processing the measured signals, and its digital outputs are connected to control inputs weighted voltage sources, pulse bi-directional current modulator, current switch, voltage switch genesis and analog-to-digital converter.

The invention is illustrated by the structural diagram and time diagram in the drawings.

Figure 1 shows a structural diagram in which:

1 - reference voltage source (ION);

2, 3, 4, 5 - sources of weighted voltage (IVN1, IVN2, IVN3, IVN4);

6, 7 - direct current sources (IT1, IT2);

8 - modulator pulse bi-directional current (M);

9 - current switch power supply of resistive sensors and resistive equivalent devices (K1);

10, 11 - resistive sensor and its resistive equivalent device (R and Rn);

12 - voltage switch (K2);

13 - instrumental operational amplifier (IU);

14 - analog-to-digital Converter (ADC);

15 - microcontroller forming a diagram of the device, receiving and executing the algorithm for processing the measured signals (MS);

16 - a source of general nutrition (E _pit. ).

Figure 2 shows a timing diagram of the operation of the device.

The device is as follows. The general power source 16 (E _pit ) supplies voltage to the reference voltage source (ION) 1, four sources of weighted voltage 2, 3, 4 and 5 (IVN1) 2, (IVN2) 3, (IVN3) 4 and (IVN4) 5, pulse bi-directional current modulator (M) 8, current switch (K1) 9, voltage switch (K2) 12, instrument operational amplifier IU 13, analog-to-digital converter (ADC) 14, microcontroller (MS) 15. Moreover, the output of the reference voltage source ( ION) 1 is connected to two inputs of the sources of weighted voltage (IVN2) 3 and (IVN4) 5, and their outputs are connected to the inputs of two sources DC power supplies (IT1) 6 and (IT2) 7, respectively. Two other sources of weighted voltage (IVN1) 2 and (IVN3) 4 are connected to the positive common power bus, and their outputs are respectively connected to the positive power buses of operational amplifiers of direct current sources (IT1 and IT2) 6 and 7. Outputs of direct current sources (IT1 and IT2) 6 and 7 are connected to the inputs of the modulator of the pulse bi-directional current (M) 8, and its output is connected to the input of the current switch (K1) 9, the outputs of which are connected to the resistive sensor R 10 (resistance sensor) and its resistive equivalent device (R _m ) 11 The potential (measuring) buses of the resistive sensor (R) 10 and its resistive equivalent device (R _n ) 11 are connected by potential buses to the inputs of the voltage switch (K2) 12, the outputs of which are connected to the differential input of the instrumental operational amplifier (DUT) 13. Analog input -Digital converter (ADC) 14 connected to the output of the operational amplifier tool (DUT) 13 with power signal U _pr., and the equivalent code converted signal to the ADC 14 is fed to one input of the microcontroller (MC) 15, and one and outputs (register) of the microcontroller (MC) 15 is connected to the control unit F tires.

The device operates as follows. From the microcontroller (MS) 15 to the sources of weighted voltage (IVN1 ... IVN4) 2, 3, 4 and 5, the control signal F1 (Fig. 2) is received, where, using switched capacitors of a sufficiently large capacity (≈100 µF), the supply voltage of the operational amplifiers is formed DC sources (IT1 and IT2) 6 and 7, as well as their reference signal from the reference voltage source (ION) 1. The following are excluded:

a) the noise component associated with the noise of active batteries;

b) the noise component associated with the need to isolate the signal of the resistive sensors (independent of the resistance of the connecting wires and switching circuits).

To increase the stability of the conversion signal, one (ION) 1 is used to set the current values in (IT1 and IT2) 6 and 7, and a pulse bi-directional current modulator (M) 8 is installed at the outputs (IT1 and IT2) 6 and 7 to switch the currents, that in the 1st switching cycle (control signal F3) (IT1) 6 feeds the resistive sensor (with resistance R), (IT2) 7 - the equivalent resistive device (with resistance R _n ), and in the 2nd cycle (control signal F4 ) conversions (Step 2) vice versa: (IT1) 6 feeds the resistive equivalent device (IT2) 7 - resistive sensor. At the same time, in order to simultaneously reduce interference from industrial frequency pickups and from voltage values arising from the temperature drift of active elements (by calculating in the code equivalent the difference of the conversion signals in Step 2 and Step 1), the outputs of the modulator (M) 8 are connected in such a way that the phase of the power signals in Step 2 is the opposite of the phase of the power signal in Step 1 (figure 2).

Conversion Output:

Beat 1:

Beat 2:

where I _n - the nominal value of the supply currents from (IT1 and IT2) 6 and 7;

ΔI ₁ , ΔI ₂ - errors of supply currents respectively in (IT1 and IT2) 6 and 7;

R _N is the nominal value of the resistance of the resistive sensor (R) 10 and the compensating resistive equivalent (R _n ) 11;

ΔR is the deviation of the resistance of the resistive sensor (R) 10 from the nominal value (R _n ) 11 (informative parameter).

The final conversion result in the microcontroller (MS) 15 in code equivalent N:

where N ₁ and N ₂ are code equivalents proportional to U _CR1 and U _CR2 ;

[I _n · (± ΔR)] informative (measured) parameter of the sensor;

[(± ΔI ₁ ± ΔI ₂ ) · (± ΔR)] is the error of the second order of smallness, which can be neglected.

Additive interference suppression is provided by the creation of weighted power supplies 2, 3, 4 and 5 (IVN2 ÷ IVN4), galvanic isolation of the reference voltage source 1 (ION) from current sources 6, 7 (IT1 and IT2), suppression of common mode noise when a measuring signal is applied to the differential input of the instrumental operational amplifier 13 (IU) and the selected signal processing algorithm in the microcontroller 15 (MS) using bi-directional pulse power supply of resistive sensors and their resistive equivalents, which ensures ostroenie low noise of a highly resistive impedance converter voltage sensors.

It should be noted that the proposed scheme for constructing a resistance converter of a resistive sensor to voltage allows you to connect strain gauge sensors (single, half-bridge, bridge, socket, etc.) using any connection scheme.

Claims (1)

A multichannel converter of resistance of resistive sensors to voltage, containing a general power source, a reference voltage source, a direct current source, resistive sensors and a resistive equivalent device, a current switch, a voltage switch, an instrument operational amplifier and an analog-to-digital converter, characterized in that a second DC source, four sources of weighted voltage, the inputs of two of which are connected to a common power source, and the outputs with are connected to the power buses of the operational amplifiers of two DC sources, and the inputs of two other sources of weighted voltage are connected to the output of the reference voltage source and their outputs are connected to the inputs of two DC sources, the outputs of the latter are connected to the inputs of the modulator of a pulse bi-directional signal, and its outputs are connected to the inputs of the current switch power supply of resistive sensors and a resistive equivalent device, and the potential bus resistive sensors and resistive equivalent The devices are connected to a voltage switch, the output of which is connected to the differential input of the instrumental operational amplifier, the output of which is connected to the input of an analog-to-digital converter connected to a microcontroller for generating a device operation diagram, receiving and executing an algorithm for processing the measured signals, and its digital outputs are connected to control inputs of weighted voltage sources, pulse bi-directional current modulator, current switch, voltage switch and analog go-to-digital converter.

Images