RU1837397C - Method of and device for functional analog-to-digital conversion - Google Patents

Description

The invention relates to measuring technique and construction of devices for the functional conversion of analog signals (thermocouple signals and thermocouples).

The aim of the invention is to increase the flow rate and expand the scope by converting signals with great non-linearity.

In FIG. 1 is a block diagram of a functional converter; in FIG. 2 - characteristic of the converter.

The functional converter comprises a normalizer 1, a reference voltage changing device 2, a reference voltage source 3, a variable resistor 4, a first adder 5, a second adder 6, an analog-to-digital converter 7 / digital indicator 8. The input of the device is connected to the input of the normalizer 1, output which is connected to the input of the first adder 5 and the input of the analog-to-digital converter 7. The reference voltage source 3 is connected to the second input of the second adder 6 and through an alternating

from co VI to u VI

a resistor 4 is connected to the second input of the first adder 5, the output of which is connected to the first input of the second adder 6. The output of the second adder 6 is connected to the reference voltage input of the analog-to-digital converter 7, the output of which is connected to a digital indicator 8.

The device operates as follows. The signal from the sensor (for example, from a thermocouple) enters the normalizer 1, normalizes to a certain level and enters the second input of the analog-to-digital converter 7. At the output of the analog-to-digital converter 7 and on the indicator 8, the number

N 1000-U - (1),

Don

where UBX is the voltage at the input of the analog-to-digital converter 7;

 - voltage at the input of the reference voltage of the analog-to-digital converter 7

The signal from the normalizer 1, passing through the circuit 2 changes the reference voltage, at the output of the device 2 implements the equation

willow, x Don + K (UBX - UBxmax), (2)

where U0n is the reference voltage of the reference voltage source 3;

ivhtah - a value equal to the maximum voltage value at the input of the reference voltage changing device 2 corresponding to the maximum value of the measured parameter (temperature);

K is the gain of the first adder 5.

Moreover, the first adder 5 implements the dependence K (UBx - UBxmax).

The voltage 1) input voltage is obtained by changing the value of the variable resistance 4, and then when the input signal of the device corresponds to the maximum value of the measured quantity (temperature) at the output of the first adder 5, the voltage should be zero. The second adder b implements the dependence

Uon + K (Uex-UBxm8X) U on.

those. U on is the reference voltage at the voltage input of the analog-to-digital converter 7, depending on the input signal of the device.

In FIG. 2 shows a voltage generating mechanism U on.

At the output of the analog-to-digital converter, a signal appears corresponding to

Don

 1000

Uon + K (Uex - Uex3)

(3)

where k

1000 - r-Uon

1mx

I, | max Uex UBX

A method of analog-to-digital functional conversion is carried out

in the following way.

The input of the normalizer 1 is fed a signal from a signal source (for example, thermocouple). In normalizer 1, the input signal is normalized (amplified and biased) to

a certain level 1) of the input, determined by the measuring range of the measured parameter. From the output of the normalizer 1, the signal is fed to the analog input of the analog-to-digital converter 7.

At the same time, the signal UBX from the output of the normalizer 1 is fed to the input of the device 2 for changing the reference voltage, to the first input of the first adder 5 A signal is sent to the second input of the first adder 5,

equal in magnitude (-UBxmax) generated by the reference voltage source 3 and determined by the magnitude of the variable resistor.

When the gain of the first adder 1 is equal to K., a signal is obtained at the output thereof, which is determined by the formula K (UBx - max.). This signal is fed to the first input of the second adder 6, to the second

the input of which is supplied a signal Uon from the reference voltage source 3. When the gain of the second adder 6 is 1, the output of the second adder has a signal

U on Uon + K (U8x - UBXmax).

This signal is fed to the reference voltage input of the analog-to-digital converter 7, in which conversion to code is carried out to control the display unit 8 in accordance with the formula iv

Nx 1000

U c

0

 1000

and

in

Uon + K (IVX -)

where NX is the code corresponding to the value of the measured parameter.

Obviously, the value of Nx has a nonlinear dependence on the input signal

5 UBX By selecting the appropriate K value

linearity of the dependence of Nx on the value of the measured parameter is achieved.

We take in accordance with GOST 3044-84 Thermoelectric converters. Nominal static characteristics of release (characteristic of TXK, XKIL), temperature measurement range from OfYO ° С,

The voltage at the output of the sensor (Beats) is measured from 0 to 6.86 mV.

In normalizer 1, the signal of the norm sensor || is emitted to a level of 0-1000 mV, while the gain of the normalizer (Kus) should be equal to 145.77. When Don e 1000

ko to mV ma I O m r et

5. °.

and Uex, 1000 mV (see formula 3) with the same input signal, we have Nx, 0. To calculate the coefficient K using form (4), we determine the value of UBX at a variable temperature of 50 ° С (it is obvious that for temperature Nx it must be equal to 0). At id 50 ° C 3.306 mV and Kus 145.77 ,,

4 / LO4GU. P

by not

-78

5

Chal Dates ISM 19,

10 U8x Kus Sig Me

fifteen

We have a Vex.50 of 481.92 mV. According to the formula 4:

100.0

481.92 50.0

-1000

481.92 -1000

0.069781.

The results of the functional conversion are given in table. 1.

The maximum error does not exceed 1 ° C, 1 ° C.

According to the proposed technical solution, a prototype was developed and tested in which block 1 of the normalizer is made on microchip KR 140 UD12 08, adder blocks 5 and 61, and chip KR140UD12 08 is a block of the known digital converter 7 on microchip KR 5 72 PV 2, display unit 8 - on MI cross circuits AL C 333.

The release of the device made according to the claimed scheme is scheduled for 1992. The existing method and device allows the conversion of signals from sources with insignificant (), 2%) non-linearity (for example, platinum resistance). With increasing non-linearity, the error in the HV conversion will increase due to the fact that the approximation of the non-linear characteristic is carried out using only two other different sections with an inflection point in the O.

The proposed method and apparatus POSE can, without loss of accuracy, convert signals from sources with significantly greater non-linearity (for example, thermometers).

In the prototype, when measuring temperature pii using thermal resistance TSP 1 (10P in the temperature range -50 ... + 50 ° C

P1

the margin of error is 0.4% 2.

6 the proposed device for TSP 1YUP in the temperature range -50 ... + 50 ° C

,,

the conversion error is not more than 0.02% (see calculation).

TSP 100P Tiem - -50 ... + 50 ° С Idvh - -78.98-119.71 Ohm.

If the normalizer 1 suppresses the initial resistance of 100 Ohms and feed the sensor with a current of 1 mA. then we can talk about changing the input signal from -20.02 to 19.71 mV.

For a display range of -50 ... 50.0 U8xmax should be 500 mV. Hence Kus 25.368 and ivht | n g-507.86 (the value of the signal at the output of the normalizer 1 at a measured temperature of -50.0 ° C)

100.0 5oo6 100 ° - 507.86 -500

-0.0155974.

The results of the functional transformation are given in table. 2.

The maximum conversion error does not exceed 0.02 ° C.

Claims (2)

SUMMARY OF THE INVENTION 1. A method of functional analog-to-digital conversion, including normalizing the input signal, generating a reference voltage, analog-to-digital conversion of the normalized signal to a code, followed by a display of the conversion result, characterized in that, in order to increase accuracy and expand the scope of application due to the conversion of signals with large nonlinearity, the formation of the reference voltage is carried out by the signal continuously according to the formula   Uon + K (UBx-UBxMaKC), where U on is the formed reference voltage; Uon is the voltage of the reference voltage source; K is a scale factor; UBX - voltage of the modeled signal; UsxMaKC is the maximum voltage value of the normalized signal. 2. A functional analog-to-digital conversion device containing a normalizer connected in series, the input of which is an input bus, an analog-to-digital converter and a digital indicator, and a reference voltage change unit connected between the normalizer output and the reference voltage input of the analog-to-digital converter characterized in that, in order to increase, accuracy and expand the scope of application due to signal transformations with high non-linearity, the reference voltage change unit full on a variable resistor, a reference voltage source and two adders, the first input of the first adder being the input of the reference voltage measuring unit, the second input through a variable resistor connected to the output of the reference voltage source, which is connected to the first input of the second adder, the second input which is connected to the output of the first adder, and the output of the second adder is the output of the reference voltage changing unit. Table 1 Table 2 OE fЈ / & 1 Vto ffff + ttox-V ™) 0. 1837397 (r) max rf T