SU1451557A1 - Device for multipoint measurement of temperature - Google Patents

Abstract

The invention relates to thermometry and allows an increase in the accuracy of temperature measurement during storage of agricultural products. The device contains resistive temperature sensors that are connected to a two-wire communication line through serial resonant circuits. The communication line, together with the temperature sensors, forms one of the arms of the bend. measuring bridge AC. In the device diagram, frequency separation of temperature channels is implemented. With the help of a block of fixed frequencies connected to one measuring diagonal. bridge, temperature sensors are polled. The second bridge diagonal includes a recorder made on the basis of an AC amplifier and a switch or digital voltage indicator. 3 il. i (Л С

Description

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The invention relates to thermometry and can be used, for example, for multipoint temperature measurement during storage of agricultural products, in greenhouses, in livestock buildings, and the like.

 The purpose of the invention is to increase the accuracy of temperature measurement. Yu

Figure 1 shows a diagram of the proposed device; figure 2 - skem Ylok fixed frequencies; Fig. 3 is a registrar circuit.

The device contains a block of 1 fixed, 5 frequency, the same frequency-independent resistors 2 and 3 of the two measuring arms, a variable-current bridge, a constant resistor 4, a switch 5 and potentiometers forming the master arm, a recorder, a two-wire line 8 and Measuring nodes 9, -9 ", consisting of Yu-Yu shements, consecutive resonant circuits and resistive 25 temperature sensors In.

The block 1 circuit of the fixed frequencies is made on the basis of a generator with an oscillatory circuit and consists of capacitors 12, -12 "connected to the input of chip 13 with the help of switch 14, capacitor 15 and inductance 16 - 18. I Circuit recorder 7 consists of an amplifier . an alternating current made on the microcircuit 19 into the {feedback circuit, which, with the help of the I switch 20, connected the submersible potentiometers 21, -21p of the phase detector 22, made on the field-effect transistor, and the diode 23 providing the required the polarity of the half-wave of the alternating voltage for synchronization of the phase detector and the measuring device (PI).

Switches .5, 14 and 20 are structurally implemented in the same housing, i.e. One three-plate switch is used to switch the measuring channels.

The device works as follows.

From block 1 of fixed frequencies to the measuring bridge of alternating current by setting the jS 14 switch to the K-th position, an alternating voltage of constant amplitude is applied with a frequency CO ,, resonant for the K-th. oscillatory; contour. Put t t h

the switch and the frequency value (O. corresponds to the number K of the currently polled measuring unit 9k. Reactive resistances and ratings of the elements of the resonant circuits are chosen such that the condition

S

one

 Utct

KU)

const,

a frequency multiplicity J

7

where i is the current number of the measuring

node.

Switch 5 to the master arm of the measuring bridge connects the tuning potentiometer 6. Potentiometers 6; These are used to compensate for the change in the active resistance of the communication line when balancing the bridge. Changes in the active resistance of a line are associated with changes in its length when interrogating various sensors, and also depend on the frequency O ;.

When polling the K-th measuring unit, its total resistance is minimal and equal to the resistance value of the resistive temperature sensor 11. The resistances of the remaining measuring units are much larger (which is achieved by the choice of the nominal 1C;) and are mainly reactive.

Using the recorder 7, the temperature at the K-th point is measured.

The AC amplifier circuit made on the microcircuit 19 provides the ability to change the gain factor by connecting the feedback potentiometers 21 using the switch 20, which allows you to equalize the sensitivity of the measuring circuit of the recorder when interrogating various measuring devices. nodes: Phase detector 22 is made on a field effect transistor and serves to obtain a constant voltage from the measured variable. It should be noted that a conventional rectifier cannot be used to rectify an alternating voltage, since it has a dead zone near zero. In addition, the phase detector allows to significantly cut off the influence of the adjacent measuring nodes when

poll one of them. The common resistances of these nodes are predominantly reactive in nature, which means that the current in these nodes is phase shifted close to 90 ° with respect to the supply voltage. As follows from the principle of operation of the phase detector, these currents will be substantially cut off. The phase detector is controlled from the output of a block of fixed frequencies. An analog or digital voltmeter can be used as a measuring instrument, calibrated in terms of temperature values.

In the proposed device, resistive temperature sensors can be used (for example, thermistors of the tep type, semiconductor thermistors, posistors of the CT11-1G type). These sensors, together with the elements of the resonant circuits, are sealed and are thickening on the two-wire communication line. All other elements of the device are structurally combined into one unit to which the two-wire communication line is connected. The device is easy to manufacture and operate, easy

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installed on agricultural objects.

Claims (1)

Claims An apparatus for multipoint temperature measurement comprising a two-wire communication line, a recorder and temperature sensors, characterized in that, in order to improve the measurement accuracy, a block of fixed frequencies and an AC measuring bridge are inserted into it, the two arms of which are formed by the same frequency -independent resistors, the third arm is made up in the form of a constant resistor and connected to it with the help of a trimming potentiometer switch, the fourth arm is formed by a two-wire A communication, parallel to which temperature sensors made by resistive sensors are connected through entered serial resonant circuits, and a recorder consisting of series-connected AC amplifier, phase detector and measuring device is connected to one diagonal of the measuring bridge, to the other diagonal of which the unit is connected fixed frequencies.  ; .I 8 9i 9p iO Jupe / 2. Ip Phie.1 H it / Fie.2 P Phases. 3