SU1758563A1 - Method of tuning tensometer bridge - Google Patents

Description

one

(21) 4826423/21

(22) 03/15/90

(46) 08/30/92. Bul Number 32

(71) Ulnovsky Research and Production Complex Center for Microelectronics and Automation in Mechanical Engineering

(72) A.I. Zhuchkov, V.A. Tikhonenkov and A.V. Ygo (56) USSR author's certificate

ISfc 1174739. Cl. G 01 B 7/18, 1985.

USSR Author's Certificate No. 1448288, cl. G 01 R 17/10, G 01 B 7 / 18,1988.

(54) METHOD FOR ADJUSTMENT OF EXTENSION BRIDGES

(57) Use: measuring equipment, when configuring strain gauge bridges, sensors manufactured by the integral and metal film technology. Summary of the invention: at the same time, the initial output signal and the temperature drift of the sensor are compensated only by external shunt resistors and a thermistor, which is structurally manufactured inside the sensor. When adjusting the sensor, it is not necessary to refine the closed bridge circuit of the sensor manufactured in a single technological cycle. 2 Il.

The invention relates to a measurement technique and can be used in setting up strain gauge bridges, sensors manufactured according to integral and metal film technology.

A known method for setting strain gages consists in inserting a thermosensitive resistor into one of the bridge arms, measuring the temperature drift of the output signal, calculating the resistance of the thermosensitive resistor required for compensation, and adjusting the resistance of the thermosensitive resistor by spraying the technological bridge .

Closest to the present invention is a method for adjusting strain gauge bridges, when temperature drift compensation is made by connecting a shunt resistor calculated from the temperature drift of the bridge output when connecting a known technological shunt, and the initial output signal is reduced to a predetermined value by fitting the resistance value of one of the strain gages (TP ) a bridge without changing its temperature coefficient of resistance (TCR),

The disadvantage of this method is the complexity, the complexity of the technology itself fitting the nominal value of the TR without changing its TKS. This is usually laser fit or mechanical cut fit, and the fit process itself requires continuous measurement of the output signal; a very high accuracy requirement for the TP fit, so for zero balancing with an accuracy of 0.2%, a precision of 0.008 Ohm is required when the shoulder resistance of the bridge circuit is 1 kΩ, as the metal film sensor has a total resistance change of the bridge circuit of 4 Ohms at the nominal value of the measured parameter.

The aim of the invention is to improve the accuracy of the sensor settings.

Xi

SP 00 SL

with

The goal is achieved by the method of adjusting strain gauge bridges to determine the resistance of bridge strain gages for two different temperatures, the shoulder to turn on the shunt resistor and calculate the value of this resistor, but unlike the prototype, the sensor simultaneously compensates for the initial output signal and temperature drift only external shunt resistors Рш, Rg and a thermistor Ra, which is structurally manufactured inside the sensor and when adjusting the sensor, it is not required to conduct processing of the closed bridge circuit of the sensor, manufactured in a single technological cycle.

The use of high-resistance shunts (Ns 20-30 kΩ) as tuning elements reduces the requirements imposed on the accuracy of their fitting to the calculated value for balancing zero, thereby increasing the maximum possible tuning accuracy.

The invention is illustrated in FIG. 1, which depicts a circuit for incorporating the design resistors Nsh and Rg into a strain gauge bridge with a thermistor Ra, 1 in FIG. 2 shows the connection of the sensor to the measuring circuit.

FIG. 1 The following notation is used: 1-4 - strain gauges Ri, R2, B3, R4; 5 - thermistor Ra; 6 and 7 - design RUI and Rg resistors.

The calculation of resistors Kr and Rg is made on the basis of tuning measurements using the formulas:

 BlC A D-C 6-D A44 b C + A D-C1a-DrA-4 (C1A-A Cl (D B-B1D), l "" ggt: -yy- :; ()

2 (С А-А С)

„Rg A H-B

 w Rg C + D

Rm -

(2

rfleA UR4Ri: A U RiR1:

B UR4RlRa; R Ral (R4 + Ri); -U1 (R4 +

() -U (R4 (Rl + Ra) + RlRa);

 (R + Rl) -U (R4 (R + Rl) + F $ Ra);

U

R4

u °. R5i

U

+ Ri Upit R4 + R

where the value of R is determined by the formula:

„I (, 7 + 4Rj, (Rt4) J (() M t uiRi / of-Rj-Ri.

Where

al (and {w1 U / Unnr: a4 (Up / Unnr:

and the value of R is found from the solution of equation (4) numerically on a computer

 f i № № frwlK l wl№ (R; lcii-K. (t}

2 (Rt / Qi-R C)

, Rl- (Ry "/ o41t2gSR -4 ((

Q The value of Ra is given by the formula

 prii-ioX: W (1 - y) of R

Rl 1 + t at i1o-i0 0; 15Ri + Ri-RVy

(five)

thirty

 Ua up r4

(-.

UnHTR + Rj,

2Q where the measured values Ri, R4 are the resistance values of the strain gauges;

Ra is the resistance value of the thermistor;

Uo is the initial unbalance of the strain gauge bridge circuit;

U about the same, at the second temperature t;

UUH is the magnitude of the unbalance of the strain-gauge bridge circuit at the second temperature t when the technological shunt RUJ is connected in parallel with the strain gauge RI;

Uui4 - the magnitude of the unbalance of the strain gauge bridge circuit at the second temperature t when the technological 35 RUJ shunt is connected in parallel with the strain gage R4;

Ua is the magnitude of the unbalance of the strain gauge circuit at the second temperature t when the thermistor Ra is connected in parallel to the selected strain gauge. 40 Selection is made as follows.

With Uo-Uo 0 Ra we connect to RI, and with Uo-Uo 0 Ra we connect to R4; ipit - voltage of food.

Example. We use the proposed method to configure a semiconductor pressure sensor DDP 001, which has

50 closed tensometric bridge circuit with a thermistor (Fig. 2). At a temperature, we measure the resistance values, 9 kΩ; , 0 kΩ; ohm; supply voltage, 0 V; the initial output signal, 845 mV, put the sensor in the furnace and heat it to At 100 ° C, measure, 687 mV, connect a comhm to RI, measure uLi 570.20 mV, connect Ksh to R / J, measure

L) U -407.43 mV. since o 0, then we connect Ra to RI and measure 51 mV.

To determine R, we solve equation (4) using the COMPENSI program (Appendix 1). The program is written in PASCAL and implements a numerical method for solving an equation of one variable using the half-division method. The lower limit of the root search interval for equation (4) is determined by the requirement of positive positivity

Rchmin -

4NS

(1 + 1 / a4) | a4G and the upper choose from the maximum

possible TKS TR: H5 | max 5.5 kOhm (TKS 0; 00375 1 / ° C); for a given accuracy of finding the root, 00001 counting time 1 s. As a result of the calculation we get

,, 4 kOhm By the formula (3) we find:

, 271 kOhm, according to the formula (5) kOhm; and using formulas (1, 2), we calculate 14 kΩ and, 371 kΩ.

After connecting the calculated values, the initial output at

, 0002 mV, and at t 120 ° C, 0014 mV; and additional temperature error caused by a change in the initial output signal:

C and 1.2 10-7 1 / ° С

otherwise At

where mV is the value of the sensor output when the nominal pressure is applied;

Thus, the calculated values gave a good compensation for the temperature error of the sensor.

Annex 1

PROFRAM COMPENS 1:

USES Printer; CONST

.five;

utsh1 0.57020;

utsh4-0.40743;

.088687;

uta .42 051;

.031845;

.9:

.0;

tol 1e-5; Var

a, b, x, fa, fb, fx, root: real;

converged: boolean;

a1, a4: real;

0

five

0

r1t, r11t, r12t: real;

rait, arg.brg, erg, ka.kb.kc.kd: real;

kat, kbt, kdt, kct1r4t, yal, nu, nut, rg, rsunt: real; FUNCTION sing (x: real): real;

BEGIN

IAx 0.0 THEN slgn: -1

ELSEslgn: 1;

END;

FUNCTION ZERO (X: REAL); REAL; Var

z.e, r: REAL- BEGIN

();

t: x / a1-x-rsh;

(x (1 + 1 / a4));

zero: (z + sqrt ()) / 2 / e +

+ {r-sqrt ((x + rsh))) / 2 / (x + rsh); END; BEGIN.

a1: (utsh1-uto) / u;

a4: (utsh4-uto) / u;

((1 + 1 / a4) (H-1 / a4) a4J;

(a); (b);

IFsign (fa) .OTHEN

wrlteln (FUNC DOES NOT CHANGE SIGN) ELSE

BEGIN

converged; abs (a-b) tot;

WHILE NOT converged DO

BEGIN

.5 (b-a); (x);

IFslgn (fa) .0 THEN

BEGIN

END

ELSE

BEGIN

END;

converged: abs (b-a) tol;

root: (b + a) / 2

END;

r11t: sqr (root) +2 rsh root;

r12t: (root / a 1-root-rsh);

r1t: (r11t + sqrt (sqr (r11t) (root) r12t)) / 2 / r12t;

r4t: root;

yal: (utal-uto) / u + r4t / (r4t + r1t);

ralt: r1 (1-yal) / (yal (r4t + r1);

{rez. determ}

(r4 + r1) -uo / u; (r4t + r1t) - uto / u;

kc: r4-nu (r4 + r1); kct: r4t-nut (r4t + r1t);

(r1 + ral) -nii (r4 (r1 + ral)

(r1t + ralt) -nut (r4t (r1t + ralt) + r1t ralt);

arg: ka kct-kat kc; brg: kct kb + ka kdt- kbt kc-kat kd;

crg: kat kb-kd kbt;

rgK-brg + sqr-t (sqr (brg))) / 2 / arg; rsunt: (rg ka + kb) / (rg kc + kd); write n (LST Compute Rg (Rsh); writeln (LST,).

writeln (LST, R1, rl: 2: 3, R4, r4: 2 3 Uo, uo: 2: 7);

Uot, uto: 2: 7);

writeln (LST, Utsht, utshl: 2: 7 Utsh4, utsh4: 2: 7.

Utal, utal: 2: 7);

writeln (LST,, ral, result- Rg, rg: 3: 4, Rsh, rsunt: 3: 4, kOm V

End.

Claims (1)

Invention Formula The method of adjusting strain gages, which consists in determining the resistance of the strain gauges located in the adjacent shoulders of the bridge, the temperature drift of the initial output signal of the bridge for two different temperatures, the shoulder for turning on the shunt resistor and calculate the value of this resistor increase the accuracy of the setting, determine the resistance of the thermistor, the connection sleeve of the thermistor, connect the shunt-up thermistor to the detected shoulder of the bridge, measure the temperature Saturn drift of the output signal bridge when a thermistor is connected, calculate the required value of the additional resistor by the formula ffleA UR4Ri; A HJIRij B UR4RiRa, - (R4 + Ri); c -Rfc -U1 (R $ + R)) (Rl + Ra) -U ((Ri + Ra) + RiRa);  (R + (Rjj (Rt, + Rt) + ft Rt).  .  ipit Rl + RI U  Pete where RL R is the resistance of the strain gauges to which the shunts are connected; Ra is the resistance of the thermistor; RI, R5i, Ra are their calculated values at the second temperature t; Uo is the initial unbalance of the strain gauge bridge circuit; U0 is the same. at the second temperature t; iPit - supply voltage, calculate the required values of the shunt by the formula Ra A + B RHI - Rg C + D and connect a thermistor Ra and resistors Rg and RUJ with the calculated values to the extracted shoulders. 1 Fig 2.