RU2790350C1 - Method for extending the range of current measured by an analogue signal converter - Google Patents

Abstract

FIELD: signals conversion and measurement.

SUBSTANCE: invention involves setting the ranges of currents/voltages to be measured and assigning a variable N for each of them and a measurement procedure including determining the range of the input analog signal by a threshold device, decreasing the reference time and increasing the voltage/current by the variable N, transferring the unchanged analog signal to the analog signal converter, the measurement procedure shall be repeated for each signal.

EFFECT: invention provides the possibility of extending the ranges measured by an analog signal converter without introducing an error in the measured signal.

2 cl, 6 dwg

Description

The invention relates to the field of conversion and measurement of signals and can be used in analog-discrete technology, namely in integrating analog-to-digital (ADC) and analog-to-discrete converters based on "voltage-frequency", "current-frequency", as well as in δ-Δ ADC.

The scheme of the widely used ADC (1) is shown in Fig. 1. The principle of operation of the converter is that the input measured analog signal is supplied to the integrator (2), and the output voltage of the integrator is proportional to the accumulated charge. The output signal of the integrator, which is the voltage level, is connected to the comparator block (3). The block of comparators connected to the integrator and logic device (4) is a device that compares the output voltage of the integrator with two threshold voltage levels.

When the output voltage of the integrator reaches one of the threshold levels, a signal is sent from the comparator block to the logic device, where the key circuit control signal (5) is generated. As a result, the comparator block determines the polarity of the input current and serves to issue a control signal to the logic device. Using the key circuit, the reference current source (6) is connected to the integrator for the reference time specified by the logic device. Thus, negative feedback is implemented by writing off the reference charge from the integrator, q _ET =i _ET ⋅τ _ET , where q _ET is the ADC reference charge, i _ET is the ADC reference current equal to the maximum possible input current. The frequency of connection of the reference current source to the integrator is proportional to the amplitude of the input analog signal. In this case, the output information of the ADC can be both a frequency and a digital code.

The output information of the ADC "voltage-frequency", "current-frequency" in the format of the frequency output has the following form - f _BbIX =i _BX / (i _ET ⋅τ _ET ), and the output frequency δ-Δ ADC has the form: (N ₊ - N _- )/(N ₊ +N _- )=i _BX /i _ET , where the weight of the smaller sample corresponds to (τ _ET ⋅i _ET ). To reduce the power consumption of the ADC, the reference current is chosen as small as possible, and to reduce the error associated with the switching edges of the reference signal, the reference time is chosen as long as possible. The operating range of such an ADC cannot be more than i _ET , and the output information cannot follow more often than 1/τ _ET . In some ADC applications, there is a task of converting an input signal that exceeds the range set for this ADC. For this, input signal amplifiers with a gain less than unity are used, and when the ADC operation range limit is reached, the gain is switched so that the input signal falls within the range [1].

The disadvantage of this method is that when using it, errors occur due to the errors of the amplifier and its leakage currents.

Closest to the proposed invention is a method for expanding the ranges of the ADC, described in the literary source "Integrating DC digital voltmeters", author V.A. Pryanishnikov, Energy, 1976, p. 153-154. This method consists in choosing the measurement limit, for which the measured voltage is fed to a high-resistance divider, the output voltage of which is fed to the amplifier and fed to the ADC, while simultaneously increasing the reference time.

The disadvantage is that this method leads to distortion of the input information due to intermediate amplification.

The objective of the invention is to create a method for expanding the measured ranges with an analog signal converter that does not introduce errors into the measured signal.

According to the proposed method for expanding the range of measured currents by an analog signal converter, the following actions are performed:

1. Set the current/voltage ranges measured by the analog signal converter and assign a variable N to each of the set ranges.

2. Determine the range of the input analog signal (current/voltage) using a threshold device.

3. Changing the reference time (τ _ET ^N ) and voltage / current (i _ET ^N ) of the analog signal converter, in accordance with a certain range by a predetermined value, N times less than the set reference time (τ _ET ⁽¹⁾ ) and N times greater than the current/voltage setting (i _ET ⁽¹⁾ ) respectively.

4. Transferring the unchanged analog signal to the analog signal converter.

5. The procedure for measuring incoming currents / voltages (steps 2-4) is repeated for each incoming signal.

When implementing this method, the reference time of the analog signal converter is reduced by N times, and the value of the reference voltage/current of the analog signal converter, respectively, is increased by N times, while maintaining the equality

i _ET ⁽¹⁾ ×τ _ET ⁽¹⁾ =i _ET ×τ _ET ^N , where

i _ET ^N =i _ET ⁽¹⁾ ×N,

τ _ET =τ _ET ⁽¹⁾ /N,

N is the measurement range expansion factor.

As a result of signal conversion in the described manner, the scale factor, resolution and sensitivity of the analog signal converter remain constant.

In addition to the above, to improve the accuracy of current / voltage measurement, it is possible to calibrate the analog signal converter in each of its additional ranges in order to eliminate the possible influence of signal fronts when connecting the reference current / voltage. In this case, when switching ranges, it is necessary to take into account the influence of the fronts of the signals when connecting the reference current / voltage, then the above-described equality takes the form I _ET ⁽¹⁾ ×τ _ET ⁽¹⁾ +q _f ⁽¹⁾ =I _ET ^N ×τ _ET ^N +q _f ^N , where q _f ⁽¹⁾ and q _f ^N are the charge of the fronts in the corresponding operating range.

In FIG. Figure 2 shows a general block diagram of a device that can be used to implement this method and includes an ADC (1) containing: an integrator (2), a block of comparators (3), a logic device (4), a key circuit (5), a reference current source (6), while the ADC (1) is additionally connected to: a block of threshold devices (BPU, 7), a range switching device (UPD, 8), a device for generating a reference current/voltage (FET, 9), a device for generating a reference time (hereinafter - FEV, 10).

Threshold devices (PD) can be built, for example, on the basis of optocouplers (two versions of such PD are shown in Fig. 3 and 4, an example of their connection for three ranges is in Fig. 5 and 6, respectively). PU are assembled into a single block - BPU, formed from the number of PU, equal to the number N of ADC operating ranges to provide three ADC operating ranges.

PU consists of two optocouplers, the inputs of which are connected in parallel with a resistor that sets the inclusion of an additional range. When the voltage drop across the resistor reaches a value sufficient to open the optocoupler, a signal is generated at the output of the optocoupler, which is fed to the UPD. The UPD is a logic circuit that outputs two digital signals to the FET and FEV, depending on the state of the MCU output. The FCD can have an additional output to indicate the range in which the converter operates, which allows using different error models for different ranges, and also allows you to distinguish between the transition to a new range and the maximum frequency of the converter when the FCD unit fails. The FEV (10) is connected to the logic device (4) of the ADC and generates the value τ _ET of the reference time. PET (9) is connected to the reference current source (6) and forms the value of i _ET of the reference current.

A universal current/voltage calibrator can be connected to the ADC to calibrate it in order to eliminate the influence of signal fronts when the reference current/voltage is connected. Without changing the value of the input analog signal, such a value of the coefficient N * is selected, at which the output frequency / ADC information does not change when switching ranges with a constant input signal.

Now τ ^N =τ _ET ⁽¹⁾ /N, ai _ET ^N =i _ET ⁽¹⁾ ×N*.

Below is an example of the implementation of the proposed method:

1. Current/voltage ranges are set on the threshold devices, the use of a separate threshold device for each range allows you to increase the accuracy when working near the boundaries of the signal conversion range.

2. Using the MCU, the range of the input analog signal (current/voltage) is determined. Each range corresponds to the number N-factor of the expansion of the measured range (in the figures shown in Fig. 5 and 6 there are three coefficients N).

3. The reference time τ _ET ^N is set on the FEV N times more than the set reference time τ ⁽¹⁾ , (i.e. the reference time of the ADC is reduced by N times). The voltage/current i _ET ^N is set on the PET N times the initial value of current/voltage i _ET ⁽¹⁾ , which allows you to convert an undistorted input signal using the ADC while maintaining resolution in all ranges of its operation.

4. The measured current/voltage from the control unit enters the ADC, the values of τ _ET ⁽¹⁾ and i _ET ⁽¹⁾ of which are changed in accordance with the coefficient N set for the range.

As an example, consider an ADC with an initial operating range of up to 12 mA (i _ET ⁽¹⁾ =12 mA, τ _ET ⁽¹⁾ =100 µs). Let the input signal range not exceed 65 mA. At the input of the ADC, an MCU is installed, containing three thresholds: 10 mA, 20 mA and 40 mA. To ensure the measured ranges, the coefficients N _i are chosen: 2 (up to 24 mA), 4 (up to 48 mA), 6 (up to 72 mA). When calibrating, 5 mA is applied to the ADC input, and the reference time is sequentially increased by 2, 4, 6 times and N _i * is determined at which the output frequency remains unchanged. These coefficients N _i *, equal, for example, 2.1; 3.95; 6.07 are entered in the UPD. In the future, in the process of converting with the help of the ADC of the input signal that caused the threshold device to operate in the BPU, corresponding, for example, to the range of 20 mA, a reference time will be set at the output of the FEV, less than N ₂ times, and at the output of the PET - a reference current greater than in N ₂ * times, in accordance with the coefficient corresponding to this range, i.e. i _ET ⁽²⁾ =12×3.95=47.4 mA, τ _ET ⁽²⁾ =100/4=25 µs.

The technical result consists in increasing the accuracy when working at the edges of the signal range and maintaining the resolution in all ranges.

Thus, a method is claimed for expanding the range of measured currents by an analog signal converter, according to which the measured current/voltage ranges are set and the reference time of the analog signal converter is changed, the peculiarity is that when setting the current/voltage ranges measured by the analog signal converter, a variable is assigned N for each of the established ranges; then the procedure for measuring the incoming currents/voltages is carried out, in which threshold devices are used to determine the range of the input analog signal, in accordance with a certain range, the reference time (τ _ET ⁽¹⁾ ) is reduced by N times and, along with it, the voltage/current (i _ET ⁽¹⁾ ) N times, while maintaining the equality i _ET ⁽¹⁾ ×τ _ET ⁽¹⁾ =i _ET ^N ×τ _ET ^N during manipulations, in which i _ET ^N =i _ET ⁽¹⁾ ×N, and τ _ET ^N =τ _ET ⁽¹⁾ /N, after which the unchanged analog signal is transferred to the analog signal converter; the procedure for measuring incoming currents/voltages is repeated for each incoming signal.

It is also possible to implement a method for expanding the range of measured currents by an analog signal converter, in which, after setting the ranges of currents/voltages measured by the analog signal converter and assigning a variable N for each of the set ranges, the analog signal converter is calibrated.

Claims (2)

1. A method for expanding the range of measured currents by an analog signal converter, according to which the measured current / voltage ranges are set and the reference time of the analog signal converter is changed, characterized in that when setting the current / voltage ranges measured by the analog signal converter, the variable N is assigned for each from the established ranges; then the procedure for measuring the incoming currents/voltages is carried out, in which, to determine the range of the input analog signal, a number of threshold devices is used, equal to the number of operating ranges, one of which is triggered when a signal arrives in the corresponding current/voltage range and sets the inclusion of an additional range by sending the corresponding signal to a logic circuit, through which, in accordance with a certain range, the reference time (τ _ET ¹ ) is reduced by N times and, along with it, the voltage / current (i _ET ¹ ) is increased by N times, while maintaining the equality i _ET ^l ×τ _ET ¹ =i _ET ^N ×τ _ET ^N , in which i _ET ^N =i _ET ¹ ×N, a τ _ET ^N =τ _ET ¹ /N, after which the unchanged analog signal is transferred to the analog signal converter; the procedure for measuring incoming currents/voltages is repeated for each incoming signal. 2. A method for expanding the range of measured currents by the analog signal converter according to claim 1, characterized in that after setting the ranges of currents / voltages measured by the analog signal converter and assigning the variable N for each of the set ranges, the analog signal converter is calibrated.

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