DD281464A5 - CIRCUIT ARRANGEMENT FOR COMPENSATING CONDENSATION RESISTANCE IN AIR CONDITIONING - Google Patents

Abstract

The invention relates to a circuit arrangement for the compensation of line resistances in air conditioning by means of bridge circuits with ohmic resistors. This type of line balance is particularly well suited if the temperature dependence plays a minor role and in which the resolution does not fall below the Meszbereich of 100 mV / K. According to the invention, when the line resistance (6) of the bridge arrangement is matched, the ohmic measuring value sensor (7) is bridged and the compensation resistor (9) arranged in the opposite bridge branch of the measuring value sensor (7) is short-circuited to use the setting controller (8) to balance the bridge and compensate for the offset voltage of the Meszverstaerkers (11) durchzufuehren. FIG {circuitry; Line resistance; bridge circuit; Meszwertaufnehmer; Compensating resistor; Meszverstaerker; Brueckenzweig; Offset voltage; Resistance; Air Conditioning}

Description

See 1 drawing

Field of application of the invention

The invention relates to a circuit arrangement for the compensation of line resistance in bridge circuits with ohmic transducers. This type of line adjustment for transducers is particularly well suited for HVAC equipment and systems, where the temperature dependence of the line resistances plays a subordinate role and in which the resolution does not fall below the measurement range of 100 mV / K.

Characteristic of the known technical solution

In air conditioning, the ohmic transducers can be operated in bridge circuits in three-wire or four-wire connection, in which the differential voltage is evaluated, or they are fed by a constant current and signal evaluation via potential measurement. The circuit arrangement of resistance measuring bridges for the control of heating and cooling installations and for the signaling of temperature limiting states are u. a. in the DD-WP 100339 set forth.

With the constant current supply of the ohmic transducers very high resolutions up to the measuring range of 1 mV / K can be realized. A disadvantage of this circuit principle is the relatively high component cost, the use of precision resistors, precision operational amplifiers and temperature-compensated constant-voltage swells for the high-precision constant-current sources. In addition, three or four conductors are needed to connect the passive transducer to the L.I3 constant current source and the high-impedance sense amplifier. This circumstance is ^; n the air conditioning technology particularly disadvantageous, 'as between Meßaufnehmorn and control or regulating device distances can occur to over 100m.

To reduce the circuitry overhead for constant current mode resistive devices, hybrid circuits have been developed by the semiconductor industry, among others.

These include a voltage controlled constant current source, an instrumentation amplifier and a matching amplifier which provides a proportional voltage signal for further measurement processing in accordance with the resistance change of the transducer.

But the disadvantages are still the currently very high cost of these hybrid circuits.

When using the resistance sensors in bridge circuits, the leads for the transducer can be reduced to two.

Since the line resistances are not automatically compensated in this circuit, they must be detected or calculated by measurement.

From WP 140922 a circuit arrangement is known in which the bridge voltage of a resistance measuring bridge is measured via an inverting operational amplifier whose output voltage is at the midpoint of two series-connected LEDs to indicate the bridge balance.

When microcomputer controls are used, the line resistances can be determined by comparison measurement to form a reference resistance and can be evaluated with the aid of an appropriate company product. However, these controls are too expensive and uneconomical in most applications in the air conditioning.

Object of the invention

The object of the invention is to simply match the Meßwortaufnehmer in the bridge assemblies with simultaneous compensation of the different line lengths and the offset voltages of Brückenmeßverstärker without the use of a microcomputer.

Explanation of the essence of the invention

The invention is based on the object, with the help of simple circuitry means to adapt the resistance of the air conditioners to the corresponding Eingangsmeßverstärker the controller to simplify the commissioning of the system and to avoid the use of additional measuring equipment.

According to the invention the object is achieved in that when balancing the Brückenschal'.ung the transducer in the Air conditioning and its corresponding resistance in the other branch of the bridge arrangement, in the Eirtgangsstufe of Regulator is housed, bridged. The compensation of the offset voltage of the measuring amplifier and the Line resistance via an adjustment in the bridge branch without line resistance. The zero point adjustment of the bridge measuring amplifier is evaluated via an additional operational amplifier, wherein

the sensitivity of the subsequent zero point indicator (ζ B. analogue instrument, AD converter with display,

LED mid-point display). When short-circuiting the transducer and the corresponding resistance in the other bridge branch during

the adjustment, the gain of the sense amplifier and thus its output voltage changes. To compensate for this, the matching amplifier for the zero point indicator must be charged with an additional voltage.

embodiment Hereinafter, the circuit arrangement according to the invention for line balance in a bridge circuit nahor

explained. Via the stabilized operating voltage + Ub, a current is fed via the series resistor 1 into the bridge resistors 2, 3, 4, 5.

The change in resistance at the transducer 7 causes a change in the bridge voltage by means of measuring amplifier

is processed and then made available at the output A for the next controller.

The input voltage required for the regulator is at the measuring amplifier 11 by the dimensioning of the resistor 12th

adjustable.

About the switch 13, the output signal of the measuring resistor 11 to the matching amplifier 16, which receives the information for

Direct control of an analog / digital converter with display unit via output B or the activation of the

Ndllpunktindikators consisting of the transistors 24,25, the protective diodes 20,21, the light emitting diodes 22,27 and the Resistors 19,23,26 to limit the current allows. Through the transistor stages, the switching method of Zero indicator improved. When adjusting the line resistance 6 of the Biückenanordnung the transducer 7 in the air conditioner to

to close and the switch 10 to close around the Kcmpensationswideretand 9. The occurring

Potential shift on the measuring amplifier 11 is compensated for by the matching amplifier 16 via the closed Switch 28 and the resistors 18,17 an additional voltage applies. The gain control of the matching amplifier is performed by the resistors 14 and 15. With the help of the adjustment controller 8 is then

the bridge arrangement and the offset voltage of the sense amplifier 11 can be adjusted.

The adjustment is made when both light emitting diodes 22,27 of the zero point indicator are dark. After the adjustment process, the bridge on the transducer 7 is removed and the switches 10,28 are opened.

Claims (2)

1. Circuit arrangement for the compensation of line resistances in the air conditioning, characterized in that bridged when adjusting the Lei'ungswiderstandes (6) of the bridge arrangement of the ohmic transducer (7) and in the opposite bridge branch of the transducer (7) arranged compensation resistor (9) are short-circuited in order to carry out the bridge adjustment and the compensation of the offset voltage of the measuring amplifier (11) with the aid of the adjusting regulator (8). 2. Circuit arrangement according to claim 1, characterized in that the potential shift at the measuring amplifier '(H) in the adjustment process is compensated for by feeding at the matching amplifier (for the zero indicator an additional voltage across the resistors, i8).