DE1616049A1 - Bridge circuit - Google Patents

Description

1516043

THE SIPPICAH COEPOHATIOF, Barnabas Road, Marlon, ■ "'' Massaehusettg, U« S · A * - ""

Bridge c h a X t u η g

· SS SS SS SSSS- «Η SS ^ SaUv S

The present invention relates to an electric see bridging position consisting of several branches, which can be compared with one in one of the branches arranged resistance, variable value and readjustment means to maintain the Adjustment state · It relates in particular to a bridge circuit whose output is opposite ii is the change in resistance of an electrical component, for example a thermistor, the resistance of which is non-linear Puncture represents the temperature.

90908771002

The bridge circuit according to the invention can be a servo device aur creation of position data. indicate which is a function of the relationship between represent a reference voltage and a measured current, these Posifcionsdaten k3ß.briert can be used to specify a variable to be measured, ζ-. B. the variable resistance of a Thermistor when subjected to variable temperature conditions.

According to the invention, the circuit is reversed in order to achieve a change in the resistance (E) proportional output variable, in one of the bridge branches a voltage source (S ») of known potential arranged. A bridge circuit is therefore in accordance with the invention provided, y / elche a plurality of interconnected and forming a zero bridge Has bridge branches, as well as a resistor which has a variable resistance value and in one of the bridge branches is connected, as well as a readjustment device to maintain the zero state (Balance state) in the bridge, whereby the bridge

circuit is characterized in that to create a current flow that has a linear! puncture to the Represents the reciprocal of the variable resistance, a reference voltage source is created, which in one of the bridge arms is connected.

909887/1002

16160ASt

"TI

Further features of the invention and its advantages emerge from the following description in conjunction with the accompanying drawings.

Here shows - ^;

Pig * 1 to 4 circuit diagrams τοη according to the known State of the art used / ended bridge circuits,

Fig. 5 is a Sehalt diagram of a bridge turret, of the basic principles of the present Invention represents

a modification of the bridge peeling after Pig. 5, including a branch to maintain alignment and

Fig. 7 is a content diagram of an embodiment a bridging circle according to the invention s ", ^ including a servo device. \

It is well known that a bridge adjustment is maintained or the Eull state is often a technical regulation element used. The tile control element can be used in the Pig. 2 to 4. Porm shown and described in more detail below be trained. . ·

In Pig. 1 form the resistors E-, E ₂ , E ₅ and E, each a bridge branch ^. In series with the resistors E, and E. is z. B. switched a powder device, for example with an iDhermistor, the corresponding resistance E is.

909887/1002

1-616 Q 4

_ 4 -

Let the line resistance of the thermistor be R, - j if the resistance of the thermistor lead is high in relation to the resistance of the thermistor to be measured, a third resistor will be IL. provided to obtain equal currents in the two halves of the bridge when the latter is balanced. The current flowing between the terminals 10 and 11 in FIG. 1 should now, as desired, be opposite to the change in resistance of the thermistor, for example. Furthermore, the starting points E ₁ and Ep for all changes in the Y / resistance of the thermistor should be kept at zero by the readjustment element.

The bridge circuits in FIGS. 2, 3 and 4 are similar to those in FIG. 1 with the exception that in FIG. 2 the resistor R is replaced by a variable resistor P.} in FIG. 3 the resistor R is replaced by the Resistor P- is replaced, and in Fig. 4 the resistor R- is replaced by the variable resistors P ₁ and P ₂ .

In Fig. 2, the high control is by a variable "Resistance P. reached in the measuring branch, its change in resistance is then complementary to the change in resistance of the thermistor.

In FIG. 3, the variable resistor P- is in the opposite position to that shown in FIG Position arranged, whereby then the change in resistance P-z corresponds to the change in resistance of the thermistor. '.

909887/1002

BADORLGiNAL

^w 1018049

-5 - - ■■ - ■ .- ■ - '■' - "■■: .- ■■ ■ '■ ■ - - ■'

In. Jig >> 4- two variable resistors F, and Pp _{running in the same direction are used, where P 1} keeps the current in both bridge halves the same, and the variable resistor P ₂ serves to balance the bridge, and the outputs E ^ and Eg to zero to hold * Vfenn _r as with a! EhennistOr, the measured one. Resistance is a non-linear puncture of a variable Sröfle (the resistance in a thermistor is a non-linear function of the "! Temperature) - / then the readjustment must also be non-linear, so that a linear output results.

Now is the ihermistor used to maintain a temperature over a range of 50 ⁰ J? (= 1Q ° 0) or more, the following difficulties arise in the circuits according to Mg. 1 to A.

The change in resistance of a rheostat like him used in Mg. 2 and 3, results in a fentaktgeräusoh {Contact noise) directly into the feedback b ^ Wv liach control a. Changes in the slope of the resistance-temperature curve will continue to be used directly as a gain change in the downstream output of the bridge Amplifier introduced. It is also a non-linear one Variable resistor or a parallel connected variable resistor required.

in Fig. 4, the potentiometers running in the same direction can be turned on generate direct contact noise which is applied to the current ^ regulation of the bridge circuit can have a detrimental effect.

909887/1002,

The gain control is also more synchronized Potentiometer limited. In addition, from the wanking From a standpoint, the use of a pair of concurrent, nonlinear, Potentiometer undesirable.

According to the present invention, the aforementioned difficulties become avoided in that a fixed tension in one of the branches of a conventional bridge of the type shown, such as in Fig. 1 is introduced. Through the introduction With such a plague voltage it is possible to determine the resistance of the thermistor by that the current flowing in the bridge is determined, without the described readjustment elements having to fall back. The reason for this goes clearly from the following analysis.

The current state of solid state operational amplifiers makes it economically desirable to have the measured variable equal to Puncture X = K. ^, or at least almost the same as this Puncture to macTien, where K is a constant and R is the Resistance is the value of which is to be determined. If a thermistor is used, a buffer resistor (not shown) can be used R can be connected in parallel to the thermistor so that a nonlinear! Did (in the form of a 3-curve) with some-i percent span is generated.

It has now been found that by introducing a fixed voltage in a branch of a conventional bridge it is possible to obtain a measuring circuit which is a reversal of the Resistance. This can be achieved by that the current flowing through the bridge changes we d until a balance is achieved, with the two halves

909887/1002

the bridge have the same current, line such Change in the current can be achieved by the. in Mg. 6 shown, later described arrangement achieved will. First, however, "with reference to Pig. the following carried out,

Assume, E * - Eo- O, i.e. h, the bridge is leveled. If E ₁ = R ₂ , then the bridge current I in R ₁ and R ₂ must be the same for IL - I ₂ to be zero. "Λ One can then set up the following equations;

^E 1:, T? 2 .. ■■■ "-: ■■ - ■; ■ ■;". ■ - ".

and 1 _T f) _ 1 TT,. 1 _T p -p

Ί ^IR L - 7 ^m L ⁺ ^ ^IR x - ^E ref

and

The current I is therefore inversely proportional to R or the resistance of the transistor in the described Embodiment. By using a fixed reference voltage therefore becomes a balanced bridge with line compensation achieved, the variable current being used as the new adjustment variable. To use this bridge, ^

'- "" -. ":" * "- 1. the comparison is retained,

2. The current can be determined.

909887 / 10Ö2

To maintain the adjustment, the size E ^ - E ₂ can be fed to an operational amplifier with a grounding input (Fig. 6). The output of the amplifier gives the supply current for the bridge. The input to your amplifier is connected in such a way that there is a negative feedback (ITa Ehreg e ment). If the gain of the amplifier is large enough, S ₁ - Ep is vanishingly small and the bridge balance is thus maintained.

It is urgent.

^e 1 = ^g3 W , ^R 1 + ^R L , ^R 1 ^{+ R} L. ^E ref

if A = gain

A (E ₁ -E ₂ ) _eBref R ₁ f

where E ~ the reference voltage, R the resistance of the thermistor, R ₁ the resistance value of one of the bridge branches and Rt the Y / resistance of the {thermistor line

Of course, you can now measure the output current a conventional, potentiometric servo system is used and the voltage drop across one in the amplifier output circuit switched on fixed resistor can be removed,

BAD GSiGiNAL 909887/1002

However, it is more advantageous :, “ftae YerhHltäis des; Jittssigangsstrom to the condition $ _Γ · _β £ · to 'attainable, which is as follows. bev / irlcii vferden fcan.iii _; ·:

¹ I was;

I _x - fir-. ■: ■ "■■■ (2)

■ - ■ -. ref ■. ■ .- "- ..

the waste in a bridge is compared with E _re £ _f the ratio of the two can be determined *

■ With ·,

2. 2 α rj Where r is a ratio zalxl branch

ref - and.Rn the resistance of a bridge used in (2), results in

You can see that J? _f, which is of interest as a practically linear of I (thermistor resistance), is directly proportional to r ,, and. also independent of

- IC; -

Equation (3) can be implemented very easily in circuit technology, as in Pig. 7, v / o the potentiometer P _{1 has} a ratio r for S _Aus> / E _re £.

P ₁ is actuated by the servo amplifier until the adjustment, at which the mechanical output then shows a display for the pctentiometer ratio r,

The following then applies to the adjustment of the servo amplifier:

IR ₂ = ^r
which corresponds to equation (3).

The circuit in Pig. 7 has the following characteristics

1. The mechanical exit, a direct puncture of r, is a measure of V. ■

2. The servo gain is just as linear as the puncture r.

5. E ^ is not critical and only affects the gain of the system.

4. The voltage at the U ^ e known R is constant _s what there of. It may be of interest where leoMion losses of the lead wires of the size of the voltage or the polarity

depend.

-Patent-aprüelie-

90S88771002

SAD

Claims (6)

- Ή '' - * 161004a Pat fen t a. η β ρ τ ii q he ί ,, Jsiectrische, consist of several sides & ej adjustable Bridge circuit. with one in one the branches arranged Value and general rules to maintain of the balanced state, thereby gelcerinseiöhiiet that in order to achieve a resistance to resistance (R ^ inversely proportional output quantity,. ■ in one of the branches of the bridge a tension cell (E f>) known potential is arranged. 2. "Circuit according to claim ί, 'characterized in that that the honor counts with such predetermined bridges are assigned, -that the bridge current up to Adjustment can be changed. 3. A circuit according to claim 2 _S wherein the bridge has four branches which are connected to one another in a ring and the connection points are set up for electrical connections, characterized in that the variable resistance to be measured (R) with the reference voltage source (Ey ₀ J .) is arranged in a bridge branch, and the Haehregelmittel have an input, which with the opposite connections at the connection points of the reference resistances (Rj V Kg »■) ..- containing branch pair and the measuring resistor Rj Rj) and the reference voltage source (E ">.) Containing branch pair is connected, and an output which is connected to the two other connections. 909807/1002 ν; - ^{:; :} bad 4. Circuit according to claims 2 or 3, characterized in that a potentiometer (P ₁ ) is provided which is connected in parallel with the reference voltage source, and secondary IJachregelmittel are provided which are connected to the bridge for setting the potentiometer. · 5. A circuit according to claim 4, characterized in that the secondary liachregeleinrichtung has a servo amplifier which has a pair of üin _t mngsansehlüsse, «one of which is connected to a junction of the bridge and the other to the potentiometer, and a servomotor for the drive the wiper of the potentiometer is provided, which is connected to the output of the servo amplifier ■ is. 6. Circuit according to one of claims 2 to 5, characterized characterized in that the primary drainage control device has an amplifier which has a large gain, and a negative level control for the bridge creates. July 6, 1967/427 909887/1002 BATH Le e f ei te