SU757876A1 - Temperature measuring device - Google Patents

Description

The invention relates to the field of thermometry, mainly to the measurement of the temperature of objects.

A device for measuring temperature is known, containing a temperature converter, a measuring circuit, a display unit [.].

However, the known device has insufficient measurement accuracy, since its operation is based on the proposal that the time constant of the temperature sensor is constant. In fact, the transient at the output of the sensor is determined not only by its own constant, but largely depends on the nature of the interaction of the sensor-measured body system: tight or loose contact (presence of thermal resistance), dry or wet sensor (sterilization in medical measurements), the nature of the body surface, heat exchange. All this leads to unpredictable changes in the constant time of the transient process and, in turn, to a large measurement error of the known device, which has a fixed setting and does not take into account these changes. thirty

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The closest to this proposal to the technical entity is a device for measuring temperature, containing a display unit, a series-connected temperature converter, a null organ, a time delay block, a storage unit, one input of which is connected to the output of the temperature converter and its control input is connected to the output block time delay [2].

However, this device has serious drawbacks - the effect on the measurement accuracy of the ambient temperature (initial sensor cooling), as well as the strong effect of a change in the time constant of the transition process at the sensor output, depending on the nature of the sensor – body system interaction, which does not allow for a significant performance gain .

The aim of the invention is to improve the measurement accuracy while simultaneously increasing the speed of the device, for which a differentiating unit, a voltage divider, a comparator, a differential amplifier, a linear adder are introduced into it.

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additional first and second storage units, with the input of the differentiating unit connected to the output of the temperature converter, the output of the differentiating unit connected to the input of the first additional storage unit and to the first input ³

the comparator, the output of the first additional storage unit is connected to the input of the voltage divider, the output of which is connected to the second input of the comparator, the control input of the first additional storage unit is connected to the output of the time delay unit, and the control input of the second - to the output of the comparator, the output of the differential amplifier soy-15 dinen with the first input of the linear adder, the output of the linear adder is connected to the input of the second additional memory block, the output of which is connected to the input of the block of the 20 and, the non-inverting input of the differential amplifier and the second input of the linear adder are connected to the output of the temperature converter, and the inverting input is connected to the output of the memorizing block, the zero-body is designed as a device for fixing the beginning of the measurement, and the second additional storage unit is designed as an analog -digital converter.

FIG. 1 is a block diagram of the device; in fig. 2 - diagrams of voltage (s) over time

The device for measuring temperature contains a temperature transducer 1, a null organ 2, a time delay unit 3, a storage unit 4, a differentiating unit 5, a storage unit 40, a voltage divider 7, a comparator 8, a differential amplifier 9, a linear adder 10, a storage unit 11 , display unit 12.

The device works as follows 45

in a way.

After connecting the sensor to the measurement volume at the output of the temperature converter 1, the voltage begins to increase (and, in Fig. 3). At time 50

the zero-body triggers and starts the exposure block 3, which after a fixed time interval fixes the voltage at the output of the storage unit 4 at the level and (and ₆ 55

in fig. 3). At the same time, the derivative of the signal at the output of the temperature transducer is formed at the output of differentiating unit 5 (and “, in FIG. 3). At time ι, the storage unit 6 fixes at 60

its output is the value of the derivative corresponding to the moment q, and then this value is fed through the voltage divider 7 with the division factor A (на ₅ in Fig. 3) to the first 65

the input of the comparator 8, to the second input of which a signal is supplied from the output of the differentiating unit 5. Information from the output of the linear adder 10 is fed to the input of the storage unit 11. At the time moment £ _{2 the} voltages at the inputs of the comparator are compared, it operates and, in turn, fixes the voltage at the output of the storage unit 11 level

^ 9 ⁺ ι-a "- ^υ πΊ)" (!)

where and _n2 is the voltage at the output of the temperature converter at the moment of time

1/1-A is the gain of the differential amplifier;

And - the transfer coefficient of the voltage divider.

This value is fixed by the display unit as a measured temperature value.

It can be shown both theoretically and experimentally that at time £ _{ζ the} value 11 ^ described by expression (1) is the exact value of the measured value 11 _t and does not depend either on the initial cooling of the sensor (and _n in Fig. 3), nor on the values of the time constant of the transient process at the sensor output. The process at the output of the temperature converter is described by the expression

-B / g

and ₄ (O = (and _{t - n} ) · (1 -ζ °) + and _n , (2)

where "С _о " is the transient time constant at the temperature sensor output.

The derivative of expression (2) (the signal at the output of the differentiating unit) will be

and; (£) = and ₄ = (and _{t -} and _n ) £ e (° C)

From the diagrams [D and Sch · in FIG. 3 and from (3) it follows that at the time moment £ ₂ (the moment of operation of the comparator) the condition

and ₄ (£ ₂ ) / and ₄ (c) = a = con ₃ £ = r (4)

Since Ιζ, (£ ^) = and _m , U (£) = and _P2 , then using expressions (2) and (4) and substituting the corresponding values in expression (1), one can easily verify that ₉ = and _t . In the proposed scheme, a point is searched automatically to transient response (£ _g), which provides elimination of the influence _of changes and b and _m in the measurement result.

The measurement time can be further reduced if the run time exposure device is not at the time _of £ (via body-zero), and when £ -0. To do this, as a null organ, you can use a fixing device for the beginning of the measurement, which can be implemented using a differentiating chain and an amplifier. Such a device is

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Strikes slow changes of the input signal to fast output with a large amplitude.

In case the device for temperature measurement should have a digital output, a single-start analog-to-digital converter can be used as a storage unit 11 (see Fig. 2), which captures a digital code corresponding to the measured value at the time.

The setup of the proposed device does not require special temperature measurements and consists only in adjusting the gain of the differential amplifier in accordance with the selected transfer ratio of the voltage divider 7 (see Fig. 2), which is an advantage from the point of view of the processability of the circuit.

The specific implementation of the proposed device is not difficult. A temperature converter, a zero-body, a differentiating unit, a comparator, a differential amplifier and a linear adder can be easily realized with the help of operational amplifiers according to standard circuitry, the time delay unit is implemented, for example, using a single vibrator, a voltage divider on the resistors, a memory unit using a key and condenser.

Comparative tests of the prototype and the proposed device under the same conditions showed a simultaneous increase in accuracy of 2-3 times and speed - 5-10 times.

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Claims (3)

Claim 40 1. A device for measuring temperature, containing a display unit, a series-connected temperature converter, a zero-body, a time delay block, and a storage unit, one input of which is connected to the output of the temperature converter, and its control input is connected 15 ,50 dinen - to the output of the time block neither characterized in that, In order to improve the accuracy and speed of the device, a differentiating unit, a voltage divider, a comparator, a differential amplifier, a linear adder, additional first and second storage units are inserted, the input of the differentiating unit is connected to the output of the temperature converter, the output of the differentiating unit is connected to the input of the first additional the storage unit and with the first input of the comparator, the output of the first additional storage unit is connected to the input of the voltage divider, the output of which the first is connected to the second input of the comparator, the control input of the first additional storage unit is connected to the output of the time delay block, and the control input of the second is connected to the output of the comparator, the output of the differential amplifier is connected to the first input of the linear adder, the output of the linear adder, the output of which is connected to the input of the display unit, the non-inverting input of the differential amplifier and the second input of the linear adder are connected to the output of the converter I have a temperature, and the inverting input of the differential amplifier memory block. 2. Device by π. 1, configured in the form of a device for fixing the beginning of the measurement. 3. Device pop. 1, characterized in that the second additional storage unit is made in the form of analog-to-digital Converter.