SU1522118A1 - Resistance-to-voltage converter with automatic selection of conversion range - Google Patents

Abstract

The invention relates to electrical measuring technique and can be used in meters with resistive sensors. The purpose of the invention is to improve the accuracy of measurements in a large range of resistances. The converter contains sensor 1, current generators 2.1-2.N, switch 3, amplifier 4, circuit breaker 5, the distributor 6 pulses. Introduction to the distributor 6 impulses made it possible to optimize the time of current flow through each sensor so that transients caused by switching are completed in the sensor, and the heat energy released due to the passage of the measuring current does not significantly warm up the sensor and distort the measurement result. 4 il.

Description

The invention relates to electrical measuring technology and can be used in meters with resistive sensors.

The purpose of the invention is to increase the conversion accuracy with a large range of resistance variations of the sensor.

FIG. 1 shows the structure of the device; in fig. 2 - time diagrams 1-1Ы, to clarify his work; in fig. 3 - the structure of the pulse distributor; in fig. 4 - time diagrams.

The device contains a sensor 1, generators 2.1-2.P current, switch 3, amplifier 4, automatic 5 select the limit of measurements, the distributor 6 pulses

The outputs of the 2.2-2.p current generators are connected to the analog inputs of the switch 3, the output of which is connected to the first output of sensor 1 and the input of amplifier 4, the output of which is connected to the analog second input of the automaton 5, the reference input of which is connected to the inputs of the generators 2.1-2.P and reference voltage terminal. The control outputs of the distributor 6 are connected to the control inputs of the automaton 5, the control outputs of which are connected to the control inputs of the switch 3.

Switch 3 contains diodes 7.1-7, p and keys 8.1-8.p, and the anodes of diodes 7 are connected via keys 8 to

bus and are the analog inputs of the switch, and the cathodes of the diodes 7 are interconnected and are the switch output.

The automaton 5 contains a comparator 9, logic elements Н-НЕ 10.1-10, п-1, triggers 11.1-11.п-1 and a decoder 12: range numbers, the outputs of which are indexes of the number of the selected measurement range, the descrambler inputs are connected to the outputs triggers 11 and are control outputs of the machine, 5..

In addition, the direct output of each n-th flip-flop 11 is connected to the first input of the P + 1-th element of AND-HE 10, and the INPUT S of each n-th flip-flop 11 is connected to the output of the U-HE 10 element.

The second inputs of the elements AND-10 are interconnected and with the output of the comparator 9, whose inputs are the analog and reference inputs of the machine 5, the third inputs of the elements AND-NO

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10 are the control inputs; the nodes of the automatic machine; the tomato 5; the inputs R of the flip-flops 11 are interconnected and are the control input of the automatic machine 5..

The number of measurement ranges is selected based on the type of resistive sensor 1 used. For example, when implementing the proposed device, it is advisable to select 4 resistance measurement ranges: the first range is within 100,000-10000 Ohms, the second 10,000-1,000 Ohms, the third 1000-100 Ohms and the fourth 100-10 Ohm The currents of stable current generators are selected as follows: 0.05 0.45 mA; 4.5 mA and 45 mA.

The current passing time from each stable current generator through the resistive sensor 1 is selected based on the transient conditions and the allowed power dissipation for this type of sensor and may be, for example, 200 μs, 20 μS, 2 μs and 0.2 μs, respectively 2.1 ... 2.p.

The period of the clock pulse driving the distributor 6 is chosen so that the average value of the power for the period dissipated at the resistive sensor 1 does not exceed the permissible power dissipation for this type of sensor.

The valve 6, triggered by clock pulses, can be implemented in various ways. FIG. 3 shows an embodiment of the distributor 6, and FIG. 4 - time diagrams that show his work. The distributor 6 in this case is built on one K-trigger 13 and eight one-shot 14-21. In this case, the output Q of each previous single-oscillator is connected to the input A of each subsequent one. The output Q of the one-shot 21 is connected to the R input of the flip-flop 13, and the output Q of this trigger, which is the output 1 of the distributor, is connected to the input B of the one-shot 14. The distributor is started by the clock pulses of FIG. 4-a, arriving at the input S of the trigger 13.

In order to simplify the design of the circuit, the RC-chain is shown only on the single-oscillator 14.

One-shot 14,16,18 and 20 are used to form time intervals that determine the mode of operation of the device

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Responsibly in the first, second, third and fourth measurement ranges (Fig. 4c, 4-d, A-f and 4-i). Single-oscillators 15, 17, 19, and 21 serve to form control pulses from the second (Fig. 4d), the third (Fig. 4th), the fourth (Fig. 4h), and reset (Fig.4-k) 5 incoming with that output of the distributor 6 to the machine 5,

The trigger 13 generates a control pulse (Fig. 4-6), arriving with. the first output of the distributor 6 on; 8.1 switch key entry. 3

The device works as follows.

In the initial state, there are no signals at the output of the distributor 6 operating in the standby mode. The keys 8.1 ... .8. P, the number of which is determined by the number of measurement ranges open and the currents from the 2.1-2.p generators pass through them. With this, no current flows through sensor 1, and there is no voltage at the input of amplifier 4 (equal to 0). When the clock pulse (Fig. 2-a) arrives at the input of the distributor 6, the first output of this distributor sends a positive signal to the control input of the key 8.1 (Fig. 2-6), this key closes and then the generator current 2.1 through the corresponding separation period 7.1 flows through sensor 1. The presence of a voltage drop across the sensor, applied to the cathodes of the separation diodes, ensures the locking of the separation: x 7.2-7 diodes. P, which prevents the generator current 2.2 ... 2.P from entering the sensor circuit. In this case, the voltage drop taken from sensor 1 is amplified by amplifier 4 and fed to the first input of the comparator 9, to the second input of which the reference voltage Cd is applied. If the resistance values of sensor 1 will be within the first measurement range, i.e. 100000-10000 Ohm, the voltage at the input of the comparator (Fig. 2-k) exceeds and, and the comparator 9 switches to the state O, and the logical O from its output goes to the first input of the logical element AND-NOT 10.1 and to the second inputs of logical elements AND-NOT 10.2 ... IO.n-1, and also to the gate input of the decoder-. torus 12,

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At the outputs of all logical elements. AND-NOT, signal 1 appears independently of the state of the signals at the other inputs. In this case, all RS-triggers 11.1 ... 11.p-1 are in the state O, in which they were set beforehand by a pulse reset (Fig. 2-e) 5 received on the R inputs of the flip-flops 11.1 ... 11.n-1 from the fifth output of the distributor 6 pulses. At the first output of the decoder 12, 1 appears, indicating that the device 1 selects a range from 5 nasty.

When a pulse appears at the second output of the distributor 6 (Fig. 2-c), the latter arrives at the second input of the NAND gate 10.1, which remains in the same state. Switching to the second and subsequent measurement ranges does not occur, since all the logical elements are AND-NOT locked with the signal O from the terminal 9.

In this case, the amplitude of the current pulse passing through the resistive sensor 1 is determined by the amount of current generated by the generator 2.1, and the duration of the current pulse is determined by the duration of the pulse coming from the first output of the distributor 6 (Fig. 2-6).

If the resistance value of sensor 1 is within another range, for example, within the fourth range, corresponding to 100-10 ohm resistance, then when a pulse arrives (Fig. 2-6) from the first output of the distributor b of pulses to the control input of the key 8.1, the last the voltage drop across the sensor also closes. 1 from the current generated by the generator 2.1, amplified by the amplifier 4 and fed to the first input

the comparator 9 is lower than the reference voltage applied to its second input, as a result of which the comparator 9 remains in state 1. Signal 1 is fed to the first input of the AND-NE 10.1 logic element of the automat 5 and the second inputs of the logical elements I- NOT 10.2 and 10.n.-1.

Similarly to the above, the currents of the 2.2 and 2.3 generators are connected to the sensor 1 under the control of pulses from the second and third outputs of the distributor 6.

Before the pulse arrives from the fourth output of the distributor 6, the currents of the generators 2.1, 2.2 and 2.3 will be connected in this way.

When a pulse arrives from the fourth output (FIG. 2-e) of the distributor 6 pulses to the third input of the logic element IO.n-1 O is applied to S

is fed to the input of trigger 11.P-1, which enters state 1 and closes the key. 8.P (fig. 2nd). Through the sensor, the total current from the stable current generators 2.1, 2.2, 2.3 begins to flow: 2.p. In this case, the voltage supplied from the output of the measuring amplifier U (Fig. 2-l) to the second input of the comparator 6, exceeds the reference voltage Ujif, supplied to its first input. The comparator enters the state O, the elements 10.1,10.2 and 10.n-G are closed and O enters the strobing input of the decoder 12.: At the fourth output of the decoder there is 1 indicating that the device has selected the IV measurement range.

When a reset pulse arrives. (Fig. 2nd) to the R inputs of the triggers 11.1, 11.2 and 11. P-1, the latter go to the initial state O, the keys 8.1 to 8. P open, the current through the sensor 1 ceases to flow and the device prdat

1522118

is prepared for boron ranges

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Claims (1)

Invention Formula Resistance-voltage converter with automatic selection of a conversion range containing a switch, current generators, sensor, amplifier, automatic selection of measurement limits, the outputs of the current generators are connected to the analog inputs of the switch, the output of which is connected to the first sensor output and the amplifier input, second output the sensor is connected to a common bus; the control inputs of the switch are connected to the outputs of the unit selection machine, characterized in that, in order to increase the accuracy of the conversion with a large In the area of change in the resistance of the sensor, a pulse distributor is introduced into it, the control outputs of which are connected to the control inputs of the automatic machine for selection of measurement limits, an analog input. which is connected to the output of the amplifier, and the reference input is connected to the inputs of the current generator and the reference voltage terminal, the clock input of the pulse distributor is connected to the terminal of the clock pulses. fig.z t t 3 and n . P Jl (rigging