SU424093A1 - DIGITAL MAGNETIC INDUCTION METER - Google Patents

Description

one

The invention relates to the field of magnetic measurements and can be used to measure, with enhanced accuracy, induction of permanent magnetic fields in a wide range of its values.

Famous digital magnetic induction meters with Hall sensors contain a series-connected automatic switch, a selective amplifier, a linear detector and a second automatic switch working synchronously with the first, a storage capacitor and an integrating RC element, with the control circuits of the automatic switches connected to the control circuit, output sensor through an isolation transformer is connected to one of the inputs of the first automatic switch, to the other input of which unplugged low resistance resistor, one of the outputs of the second automatic switch connected via the integrating unit to one of the inputs nulorgana and the other output of the switch is connected to the second input nulorgana to which is also connected to a storage capacitor.

However, in a known device, the temporal and temperature instabilities of the parameters of the elements of the integrator and the generator of counting pulses can affect the measurement result. Besides.

the measurement error introduced by the memory element appears.

To improve accuracy, the meter of the proposed design is equipped with a voltage source, a code-voltage converter and a memory register, while the register inputs are connected to a counter, and the outputs are connected to the code-voltage converter inputs, the output of which is connected to one contact of the second an automatic switch, the other contact of which is connected to the source of the reference voltage, and the output to the integrator, the control circuits of the memory register and the circuit for setting the counter to the zero state are connected to the control circuit Yeni.

FIG. I shows a block diagram of a digital magnetic induction meter; in fig. 2 - time diagram of voltages.

In the block diagram shown in FIG. 1, included: a selective amplifier 1, a linear detector 2, an automatic switch 3, a low-resistance resistor 4, a Hall sensor 5, an alternating current source 6, a zero-organ 7, an integrator 8, an automatic switch 9, a reference voltage source 10, a generator clock pulses 11, control circuit 12, key 13, counting pulse generator 14, counter 15, memory register 16, voltage-to-code converter 17, balancing

trapsforgator 18, digital reading device 19.

The measurement is performed in two cycles. In one cycle to the input of the selective amplifier 1, connected to the linear detector 2, through an automatic non-switch 3, the voltage is removed from the low-impedance resistor 4 included in the center of the Hall sensor 5 from the AC source 6. Reinforced and rectified voltage is fed to one of the inputs of the null organ 7 is determined by the expression

u, k, kjcpR., (1)

where ki is the gain of the amplifier; kz - linear transmission coefficient

detector;

/ sr - the average value of the rectified power supply current of the sensor;

A dc is an impedance resistor in the sensor supply circuit.

The other input of the zero-body 7 receives a linearly varying voltage from the output of the integrator 8, to the input of which through the automatic switch 9 a signal is supplied from the source of the voltage 10. The slope of the linearly varying voltage at the integrator's output is determined by

tg0. . (2)

where 6 is the angle of inclination of the linear structure;

iJon - the design of the reference ntochnik; T is the integrator time constant. Simultaneously with the start of the sweep of the linear voltage, the generator of clock pulses 11 through the control circuit 12 with the help of a switch 13 connects the output of the generator of counting pulses 14 to the input of the counter 15.

In case of equality of the compared voltages, the null-organ 7 by means of the key 13 disconnects the counter 15 from the generator of counting pulses 14. The number of counted pulses will be equal to

L. Af, (3)

where / 1 is the time interval

/ is the frequency of the counting pulse generator.

In accordance with the notation adopted on the fng. 2, we have

. ,

Substituting in (4) the expressions (1) and (2), we obtain

 Y, YA / Wed / O7

Z

f / on

Then the number of pulses of the SU in accordance with (3) and (5) is equal to

l / l i z cpKaTf

l 1.

/ op

Thus, at the end of the first measurement cycle, the number of counted pulses L will be fixed by a counter in the form of a digital static code, which is transferred to the memory register 16 by a signal from the control circuit 12 and converted by means of a voltage-code converter 17 to the corresponding voltage 1/2, determined by vyralseny

ft „„ k k-iffpRfiTf

(7)

Lj n - ill - -

f / on

where t is the inverse transform coefficient.

In the second measurement cycle, the output amplifier of the sensor 5 is fed to the input of the selective amplifier 1 via an automatic switch 3 and a balancing transformer 18. In this case, the rectified voltage bz at the input of the zero body 7 will be equal to

and, - Sk, k, I, B, (&)

where S is the specific sensitivity of the sensor to

induction;

B - measured magnetic induction. The other input of the zero-body 7 receives a linearly varying voltage from the output of the integrator 8, to the input of which through the automatic switch 9 is supplied the voltage from the output of the voltage-code converter. The slope of the linear voltage at the output of the integrator will be determined by the expression

if.

mktkffcpRof

tge .--

(9)

In the future, the operation of the circuit is similar to the nerve measurement cycle. The number of counted pulses will be equal to

L. t, l

(ten)

where ga is the time interval.

In accordance with the notation in FIG. 2 we have

t. tge

(P)

(Ii) expressions (8) and (9), by

(12) mRaf

the number of NZ impulses in accordance with (12) is equal to

L /, - 1 V.

(13) mRo

Denoted °

through the coefficient of proportionality of k, we have

L, kSB. (14)

Thus, the input of the counter 15, set to the beginning of the second measurement cycle, to the zero state by a signal from the control circuit 12, receives the number of pulses NZ, which the counter will record as a digital static code. The state of the counter is indicated by the digital reading device 19.

The automatic switches 3 and 9 are connected via a control circuit 12 to a clock pulse generator 11, which performs a push-pull sequence of conversions.

Based on expression (13), which does not include parameters such as the integrator time constant, the frequency of the generator of counting pulses, the transmission coefficients of the selective amplifier and the linear detector, and the sensor supply current, it can be concluded that the number of counted pulses is L / 2 proportional to the measured magnetic induction and does not depend on the change in the transmission ratios of the amplifier and detector and the instability of the sensor supply current, or on the change in the parameters of the elements of the integrator and the generator of counting pulses. In addition, the meter circuit does not contain a memory device, which eliminates measurement errors due to the instability of its parameters.

Subject invention

Digital magnetic induction meter containing a Hall sensor with balun

an output transformer and a low-resistance resistor in the sensor supply circuit from an AC source, connected in series by an automatic switch, a selective amplifier and a linear detector,

connected to one input of a null organ, the other input of which is connected via the integrator with a second automatic switch operating synchronously with the first, and the output with the first input of a key, the second input of which is connected to the output of the counting pulse generator, the third input is through a control circuit the output of the clock generator, the output of the key, via a counter, is connected with a digital reading device, which also, in order to increase accuracy, is equipped with a reference voltage source, a "code-voltage" converter and a memory register, the inputs of which are connected to the outputs of the counter, and the outputs are connected to the inputs of the code-voltage converter, the output of the latter is connected to one contact of the second automatic switch, the second contact of which is connected to the output of the reference voltage source.