DE1182873B - Linear temperature measuring circuit - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Kl .: GOIk

German class: 42 i- 7/01

Number: 1182 873

File number: H 44544IX b / 42 i

Filing date: January 5, 1962

Opening day: December 3, 1964

The invention relates to a linearly indicating, at least one temperature measuring resistor with a linear characteristic in a bridge circuit having temperature measuring circuit with one of the Measuring bridge for the purpose of display linearization upstream network.

Such temperature measuring circuits without an upstream network have already become known at which the linearity of the display characteristics by appropriate dimensioning of the resistances of the Measuring bridge is sought, but a linear display characteristic only approximately and only is achieved in a limited measuring range.

An approximate linearization of a measuring arrangement has also already been proposed by interposing a network, e.g. B. a series resistor or a T-link between Voltage source and measuring arrangement to achieve. The intermediary network will also A correction of the display characteristics can only be achieved over a limited measuring range.

In addition, it is known per se, a non-linear display characteristic by means of an intermediate Correct bridge, d. This means that the characteristic should also be changed here so that a a practical linearization is achieved in a limited measuring range.

The temperature measuring circuit according to the invention differs from these known circuits in that the temperature measuring bridge is in the diagonal branch of a second, downstream of the rectified alternating current supplying supply voltage source Bridge with one temperature-independent resistor each in three bridge branches and at least a rectifier in the fourth branch of the bridge and that the resistances of the intermediate Bridge are dimensioned such that the diagonal voltage characteristics of the intermediate bridge as a function from the change in load due to the measuring bridge from the linearity in the same size, but deviates in the opposite direction as the display characteristic which occurs without the intermediate bridge the measuring bridge. In this way, a precise linearization of the display characteristics can be achieved.

The invention is explained in more detail using an exemplary embodiment shown in the drawing.

F i g. 1 is a circuit diagram of an embodiment;

Figure 2 is a graph of the various elements;

Linear temperature measuring circuit

Applicant:

Hagan Pneutronics S. A., Geneva (Switzerland)

Representative:

Dipl.-Phys. H. Schroeter, patent attorney,
ίο Munich 5, Papa-Schmid-Str. 1

Named as inventor:
Emil Joseph Poshadel, Mt. Lebanon, Pa.,
¹ S George Eibin Phillips, Craftön, Pa. (V. St. A.)

Claimed priority:

V. St. v. America March 9, 1961 (94 593)

F i g. Fig. 3 is a section through a probe showing the temperature-dependent resistances.

In the drawing, an egg-passage bridge shell 10, a temperature-sensitive bridge circuit 11 and a power source 12 are illustrated.

The power source 12 supplies a high-voltage to 120 volt alternating current to the terminals 13 and 14 of the primary winding 15 of the transformer 16. The secondary winding 17 is connected to the bridge circuit 10 via a diode 18 and a filter circuit, the resistor 19 (750 ohms ) and capacitors 20 and 21 (20 microfarads each). One branch of the bridge circuit 10 is provided with Zener diodes 22 and the other branches with resistors 23, 24 and 25 which are selected in such a way that they compensate for the internal resistance of the diodes 22.

The temperature-sensitive bridge circuit 11 is provided with two sensors 26 and 27 (highly temperature-sensitive resistors with positive temperature coefficients) in opposite bridge branches and with balancing resistors 28 and 29 (700 ohms) in each of the other branches. The output from the bridge circuit 10 is supplied to the bridge circuit 11 on a terminal 30 between sensistor 26 and resistor 29 and the terminal 31 between sensistor 27 and resistor 28. A resistor 32 (400 ohms) can be arranged in one of the feed lines from the bridge 10 to the bridge part in order to emphasize the voltage drop across the bridge circuit 10 . The outcome of the

40 «730/156

Bridge circuit 11 is connected to terminal 33 between Sensistor26 and resistor 28 and the Terminal 34 between the Sensistor27 and resistor 29 on a measuring or recording device 35, like a registering ammeter.

The sensors 26 and 27 are advantageously inserted into the end of a hollow stainless steel tube 36, which is housed in a protective probe 36 a, which extends into the material, its temperature is to be determined. Conductors 37, 38, 39 and 40 extend from the sensors through the tube 36 for connection to terminals 30, 31 and 33, 34 of the bridge circuit 11. The sensors 26 and 27 are advantageously embedded or encapsulated in the end of the tube 36 in a casting resin.

In the arrangement described above, the curve of the bridge circuit output with constant supply voltage and two linear active sensor elements is shown as A in FIG. 2 shown. The curve of the supply voltage at the output terminals of the bridge circuit 10 as a result of the bridge load is shown at B as a function of the temperature. The linear output on the recorder is labeled C as temperature.

The deflection bridge circuit described above yields a voltage (C) proportional to the bridge imbalance. In order to achieve the greatest inequality at a given temperature, two sensistors 26 and 27 with high temperature coefficients are connected in opposite bridge branches. Since sensistors have a much higher temperature coefficient that increases with temperature than normal resistor elements, a greater bridge linearity is achieved than with normal resistors. The use of two sensors in the bridge circuit 11 results in double the linearity correction as well as double the gain. Since the sensors have a positive temperature coefficient, the bridge circuit 11 represents a load on the power source that decreases with temperature. The character of the power source is such that it is only influenced by changes in the load. As the load decreases, the voltage supplied to the bridge circuit 11 increases, and by adjusting the supply source impedance correctly to the bridge impedance through the resistor, the voltage supplied to the bridge (curve B) can be adjusted to compensate for non-linearity of the bridge (curve A) . By using the zener diodes 22, the voltage from the bridge circuit 10 is not affected by changes in temperature or AC supply voltage.

Claims (2)

Patent claims: 1. Linearly indicating, at least one temperature measuring resistor with linear characteristics in bridge circuit having temperature measuring circuit, with a network connected upstream of the measuring bridge for the purpose of display linearization, characterized in that the temperature measuring bridge in the diagonal branch of a rectified alternating current supplying supply voltage source connected downstream second bridge, each with a temperature-independent resistor in three bridge branches and at least one rectifier is located in the fourth bridge branch and that the resistances of the intermediate bridge are dimensioned in such a way that the diagonal voltage characteristic of the intermediate bridge, depending on the load change caused by the measuring bridge, deviates from the linearity in the same size but in the opposite direction as the one without the intermediate bridge adjusting display characteristics of the measuring bridge.
2. Temperature measuring circuit according to claim 1, characterized in that the measuring bridge in the A resistor is connected upstream of the diagonal branch of the intermediate bridge. Documents considered: German Patent No. 848 420; "Journal of Scientific Instruments", 1951, p. 176; "Electronic Engineering", February 1953, p. 55; J. Krönert, "Measuring bridges and compensators", I. Teü, 1935, pp. 107 to 117. 1 sheet of drawings «9 730/156 11.64 © Bundesdruckerei Berlin