RU1798626C - Capacitive converter - Google Patents

Description

venno d Cz. The GTI 8 generates at its output a sequence of pulses spaced apart by T / 2 (T is the generator period), providing also a process spaced apart by T / 2. The d-bit of the sensor capacities is charged, while pulses ri are generated at the outputs 20-21 of the PWM 3. G2, the durations of which are determined by the values of Ci, C2 (Fig. 3a); they are also spaced at T / 2.

MFP 2 generates differential voltage ± AU; U2 Uo + AUnofl by the action of the output voltage of the integrator, while at Uvy OUi U2 Uo. The output voltages of the MFP 2 also set the differential-changeable values of the currents DIT 1 according to the equations:

And 0 ± D1; 12 1o + A,

where o is the value of currents DIT 1. corresponding to the value

Ui, 2 Uo const.

Therefore, for the value X 0, when Ci € 2 J1 - 12 Q and. PWM 3 generates pulses of the same duration T | G2

Unop is the threshold voltage of the PWM 3. In this case, the multi-polarity pulses at the output of the switch do not contain a constant component at the voltage outputs 28 and 29

U- U 0.

At a static value X Xo (position 2 of Fig. 2) Ci C2, with the result of the passage of X Ho on; the output of the switch will be the presence of different-polarity pulses of different durations

T1. T2. the constant component (Q-Uota) / T contained therein will be selected by filter 5, and the output voltage of the ID 6 will increase until the voltage at the inputs of the ID 6 is equalized through the feedback loop. Since the potential of the non-inverting input of the DI 6 0, then, going back from the inverting input of the DI 6 through the transmission coefficient of the constant component of the filter B Kf, we obtain the equality of the pulse duration at the output of the switch:

Uori -Uor2 p4- -Q

T.Kf 7

t -T2 COnSt

which will be provided with the above equations of MFP 2 and DIT 1, therefore

- UnopC2. Ci C2 -

12

 AND

const

those. the feedback loop allows the H.2 currents to copy the change in capacitances Ci, C2 (the curves of variation of And, 2 superimpose the variation of Ci, C2 of Fig. 2), therefore, the feedback loop will shift the pulses of different duration appearing at the first moment to pulses of the same duration (Fig. 36 kfig. Over). Thus, the OS circuit operates in a mode of maintaining a constant value of the PWM signal component equal to zero.

From the condition of balancing the result of passing the measured value X to the inverting input of DI 6 at voltage U-, we find the transfer coefficient between the value of X and the output U-:

. .

X Cd -Kshim (g / s) But Kf

 U KmFP K | K shim (g / o Kf Do

KdKshim (g / s)

K MFP K | K PWM (T / G).

X

 Ki -X,

where Cd is the transmission coefficient of the sensor;

Kshim (g / C) - PWM 3 transmission coefficient relative to the change in sensor capacitance;

KmFP - transmission coefficient of MFP 2, - Ki - transmission coefficient of DIT 1; Kshim (t / 1) - PWM 3 transmission coefficient relative to current. As a result of copying by the currents And, r the values of d, C2 and the sum (Ci + C2) are copied by the sum (And + h) and, since it is formed in feedback, then with respect to the sensor the measurement function:

U K

Ci-C2 Ci + C2

because the product of Cd X is proportional to the differential change in capacities (Fig. 2) Cd X (Ci - C2), and the quantity (I + fc) is proportional to their sum:

K MFP K | K PWM (G / O

s (li + l2) s (-Ci + C2)

With a dynamic change in X Xo + + XmSfn of the input parameter (position 3 of Fig. 2), a component of the PWM signal acts at the output of the switch, equivalent to its amplitude Xm (Fig. Sv), while If the OS is closed for a constant component and open for a variable, then the output voltage of DI 6 along the OS circuit at the output of the switch will eliminate the constant component of the PWM signal (similar to the previous case), and the remaining component will be selected by the demodulator 10.

Thus, at the output of ДИ 6 it will have a constant voltage proportional to the constant component of the input parameter, and at the output of the demodulator it will have a variable voltage proportional to its amplitude:

U / IT K Xt

K-CD KSHIM (G / S) Kdem Uo

where Kdem is the transmission coefficient of the demodulator.

Claims (1)

The claims A capacitive converter containing a differential current source, a pulse-width modulator, the timing of which the inputs of which are connected to two capacitors of the sensor and the outputs of the current source, and pulse outputs - with control inputs of a switch connected to a filter, a differential integrator whose output is a constant voltage output, whose inverting and non-inverting inputs are connected to the filter output and common bus, clock generator, forward and reverse outputs which are connected with pulse-width modulator start inputs, a bipolar voltage source connected to the analog inputs of the switch, a scaling converter, the scale and control inputs of which are connected respectively to the negative reference voltage output of the bipolar source and high. differential integrator, and outputs with control inputs a current monitor whose reference input is connected to the output of the positive reference voltage of a bipolar source, with the exception of the fact that, in order to expand the functionality, a linear pulse-width demodulator is introduced into it signals, the input of which is connected to the output of the switch; the output is the output of the AC voltage of the converter. Fchg. 1