DE2332943A1 - ELECTRICAL CIRCUIT ARRANGEMENT TO REDUCE THE TEMPERATURE DRIFT OF BRIDGE CIRCUITS - Google Patents

Description

Electrical circuitry to reduce temperature drift of bridge circuits The invention relates to an electrical circuit arrangement to reduce the temperature drift of bridge circuits, at least partially consist of temperature-dependent resistors.

In many cases, temperature-dependent electrical resistances are used for measuring purposes used. In order to eliminate the influence of the ambient temperature, these become temperature dependent electrical resistances often to electrical bridges, e.g. to the well-known Wheatstones Bridge, switched.

A major disadvantage of these bridge circuits, in particular When very accurate measurements are required, it is important to that due to differences in the temperature-resistance characteristics of the individual temperature-dependent Resistances with changing ambient temperature at the bridge diagonal an error signal occurs as a function of the bridge temperature, which superimposes the correct signal will.

The object of the invention is to avoid the inevitable Differences in the temperature-resistance characteristics of the individual temperature-dependent To reduce or eliminate error signals resulting from bridge resistance, that a sufficiently correct signal is obtained even for very precise measurements.

This object is achieved according to the invention in that an organ to determine at least one of the temperature-dependent tarp for the temperature Bridge resistance state representative signal is provided and that this signal is used as a correction signal to compensate for the temperature drift of the bridge.

Further advantageous embodiments and features of the invention result from the subclaims.

The invention is described below on the basis of exemplary embodiments Referring to the drawing explained in more detail; in the drawing shows: Fig. 1 a Circuit diagram of the known Wheatstong bridge, Fig. 2 + 3 two embodiments the circuit arrangement according to the invention, in which the temperature measurement the Bridge resistances are traced back to a resistance measurement, and FIG. 4 + 5 basic circuit diagrams to explain the evaluation of the correction signal obtained.

Fig. 1 shows the known Wheatstone bridge with the supply voltage connections 1 and 2, as well as the bridge diagonals with connections 3 and 4 and the resistors 5,6,7 and 8.

According to Fig. 2, the temperature measurement of the bridge resistances is based on a resistance measurement is fed back. The feed stream of the bridge (5,6,7,8), the consists at least in part of temperature-dependent resistors, generated at the resistor 16 a voltage drop. This voltage drop depends on the bridge resistance and thus a measure of the temperature of the bridge's resistances. The feed takes place via terminals 12 and 13, while the temperature-dependent correction signal is sent to the Outputs 14 and 15 is available.

The temperature measurement is also carried out in the circuit arrangement according to FIG of the bridge resistances are traced back to a resistance measurement. The least partly temperature-dependent bridge resistors 5,6,7 and 8 form a variable one Resistance of another resistor arrangement, also to be considered as a bridge from the resistances or resistance groups 9,10,11 on the one hand and the resistances 5,6,7 and 8 on the other hand.

The power is supplied to one of the bridge diagonals, e.g. 12 and 13 and on the other diagonal 14, 15 there is an output signal as a function of the temperature of resistors 5,6,7 and 8 are available.

A temperature measurement of the bridge resistances can according to an advantageous Embodiment can also be made indirectly by a sensing element. Included it must be taken into account that the sensor element has a small thermal mass and must be thermally very closely coupled with the bridge resistors.

The best thermal coupling is achieved when the sensor element is in is made in one piece with the bridge resistors. Depending on the sensor used if there is a voltage or a resistance at the output as a function of the bridge temperature to disposal.

The correction signal can be evaluated as follows: The correction signal 14, 15 tapped at terminals 14, 15 (FIGS. 2 and 3) arrives to the inputs 18 and 19 of an operational amplifier 17. The amplified signal affects at least one resistor 16 in the bridge 5,6,7 and 8 such that the temperature drift is corrected. The resistor 16 can be a motor-driven one Acting potentiometer, which is controlled by the output signal via a follow-up control of the amplifier 17 is driven. It is also possible that this is the case Resistance is a magnetically controllable element; in this case feeds the amplifier output an electromagnet.

Likewise, the resistor 16 can consist of an indirectly heated thermistor besihen, whereby the amplifier feeds the heating coil that heats the thermistor Has. The resistor 16 can analogously at different points on the bridge and therefore also parallel to one of the resistors 5,6,7 or 8, for example.

In the arrangement according to FIG. 5, the correction signal is transmitted via an adapter 20 superimposed on the bridge signal in such a way that the temperature drift of the bridge is compensated will. The overlay can be done directly at the bridge exit; it however, it is also possible to carry out the correction in a possibly subsequent amplifier before increase.

- patent claims -

Claims (10)

Claims 1, electrical circuit arrangement for reduction the temperature drift of bridge circuits, at least partially from temperature-dependent Resistances exist, as a result of the fact that an organ is used to Determination of at least one of the temperature-dependent bridge resistances for the temperature representative signal is provided and that this signal as a correction signal is used to compensate for the temperature drift of the bridge. 2. Circuit arrangement according to claim 1, characterized in that g e k e n n -z e i c h n e t that the organ to determine the correction signal in the feed circuit the bridge is switched and the correction signal is tapped at the terminals of this organ is. 3. Circuit arrangement according to claim 2, characterized in that g e k e n n -z e i c h n e t that the organ to determine the corrective event from a resistance (16) exists. 4. Circuit arrangement according to claim 1, characterized in that g e k e n n -z e i c h n e t that the bridge circuit with the at least partially temperature-dependent Resistors (5,6,?, 8) in total as a variable resistance in another bridge (9,10,11; 5,6,7,8) switched and the correction signal on the unpowered bridge diagonal (14,15) is tapped. 5. Circuit arrangement according to claim 1, characterized in that g e k e n n -z e i c h n e t that the organ for determining the correction signal from a sensing element small thermal mass. 6. Circuit arrangement according to claim 5, characterized in that g e -k e n n z e i c h n e t that the sensor element with at least one bridge resistor thermally is closely coupled. 7. Circuit arrangement according to claim 6, characterized in that g e -k e n n z e i c h n e t that the sensing element is part of at least one of the bridge resistors forms. 8. Circuit arrangement according to one of the preceding claims, characterized it is not noted that the correction signal has at least one additional Resistance (16) in the bridge influenced. 9. Circuit arrangement according to claim 8, characterized in that g e -k e n n z e i c h n e t that the resistor (16) is in series or in parallel with one of the bridge resistors (5,6,7,8) is switched. 10. Circuit arrangement according to one of the preceding claims, characterized it is noted that the correction signal by means of an adapter (20) is superimposed on the output signal of the bridge.