RU2027142C1 - Method of temperature compensation of resistor strain gauges - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: initial input signals of the gauge are measured at two values of temperature operation range Thermo-sensitive resistor is connected to one arm of bridge circuit. Then the gauge is pressurized at normal climatic conditions. EFFECT: improved precision of measurement. 1 dwg

Description

 The invention relates to measuring equipment and can be used in the design and manufacture of strain gauge sensors.

 There is a method of compensating the effect of temperature on strain gages, in which the working and compensation strain gages are installed at the measurement site and connected to adjacent shoulders of the measuring bridge circuit, and the compensation strain gage is mounted on an elastic microbarrel and deformed so that the deformation of the compensation strain gage is adequate to deformation of the working strain gage (a .s. USSR N 305347, 1971).

 The disadvantage of this method is the complexity of the technical implementation, especially in modern sensors having small dimensions and weight, as well as low accuracy of compensation due to the impossibility of obtaining the same deformation of the compensation and working mesoresistor.

 There is also known a method of thermal compensation of resistance strain gauges, in which compensation strain gages are glued to the compensation plate and included in the adjacent shoulders of the bridge symmetrically with working strain gauges glued to the part, and the same temperature-dependent resistance is additionally glued to the part and compensation plate, depending on the signs of the temperature resistance coefficients working and compensation strain gages in the corresponding shoulders of the measuring bridge (A.S. USSR N 311133, 1971).

 The disadvantage of this method is the low accuracy of compensation due to the spread in the characteristics of strain gauges and thermally dependent resistances and the influence of adhesive layers. In addition, the processability of the process of thermal compensation is small due to the presence of a large number of such difficult to control operations as a sticker, the manufacture of a compensation plate with the required thermal and elastic characteristics. The closest technical solution to this invention is a method of temperature compensation of strain gauge sensors, which consists in the fact that the sensor is heated, the magnitude and sign of the temperature error are determined, which calculate the magnitude and location of the thermosensitive resistor and include it in the bridge circuit, while the thermosensitive resistor is placed in a sealed vessel, which before turning on the thermosensitive resistor in the bridge circuit and determining its location is evacuated, and then yshayut pressure in the vessel until the temperature in a compensation (AS USSR N 805061, 1981).

 The disadvantages of the method are the difficulty of technical implementation due to the need to use sophisticated calibration and testing equipment, which is required to evacuate the vessel and maintain the necessary pressure in it; low accuracy of thermal compensation, especially at sufficiently high rates of temperature change of the medium being measured due to the significant thermal inertia of the temperature-sensitive resistor-gas-vessel system, since gas has a low thermal conductivity.

 The aim of the invention is to improve the manufacturability of thermal compensation.

(1) где S - чувствительность датчика;
R - сопротивление плеча мостовой схемы датчика;
α_β - температурный коэффициент сопротивления материала термочувствительного резистора, и герметизируют датчик в нормальных климатических условиях.The goal is achieved in that in the method of temperature compensation of strain gauge sensors, including measuring the initial output signals at two values of the operating temperature range, calculating the magnitude and sign of the change in resistance of the heat-sensitive resistor, turning it on depending on the sign of the change in resistance in one of the arms of the bridge circuit, determine the initial sensor output signals for sealing, after which the calculated resistance of the thermosensitive resistor is changed by an amount selected from the ratio shenia (1)
Δr _β = 0.01465S

(1) where S is the sensitivity of the sensor;
R is the shoulder resistance of the sensor bridge circuit;
α _β is the temperature coefficient of resistance of the material of the thermosensitive resistor, and the sensor is sealed under normal climatic conditions.

 The drawing shows the connection of measuring devices to the sensor when implementing the proposed method of thermal compensation.

 The drawing shows the electrical output conductors 1-8 of the sensor, a strain gauge sensor 9 subjected to thermal compensation, a power source 10, a measuring device-voltmeter 11.

(2) (Осадчий Е.П. Проектирование датчиков для измерения механических величин/М.: Машиностроение, 1979, с. 67).PRI me R. The terminals 1-8 of the strain gage sensor in an unsealed state are connected to the power source 10 and the measuring device 11. After a five-minute heating of the sensor by the power current, the initial output signal U _оb1 is measured using the measuring device under normal climatic conditions. Next, the sensor is placed in a thermostat with liquid nitrogen and kept at minus 196 ^o C for at least 40 minutes and this temperature was measured at the initial output signal U _ob2 sensor. After that, calculate the magnitude and sign of the change in resistance of the heat-sensitive resistor in a known manner, for example, by the formula
r _β =

(2) (Osadchiy E.P. Design of sensors for measuring mechanical quantities / M.: Mechanical Engineering, 1979, p. 67).

Here K is a coefficient equal to the ratio of the resistances of the nearby resistors of the bridge circuit, in our case K = 1;
U _pit - sensor supply voltage;
t ₁ - temperature - normal climatic conditions;
t ₂ = 196 ^about C.

(3) где S =

S - чувствительность дат- чика;
U_вых - выходное напряжение датчика;
Р_н - номинальное измеряемое давление;
R - сопротивление одного плеча мостовой схемы;
α_β - температурный коэффициент сопротивления материала терморезистора.Next, it is determined by what value it is necessary to change the calculated resistance of the thermosensitive resistor from relation (3):
Δr _β = 0.1465

(3) where S =

S is the sensitivity of the sensor;
U _o - the output voltage of the sensor;
P _n - nominal measured pressure;
R is the resistance of one shoulder of the bridge circuit;
α _β is the temperature coefficient of resistance of the material of the thermistor.

The values of U _o , U _pit , R _n are taken from the technological passport to the sensor, S is calculated, and α _{β is} taken from the certificate for the material of the heat-sensitive resistor in relation to (4):
R _β = r _β + Δr _β (4) and a thermally sensitive resistor with a resistance value equal to R _{β is} manufactured in a known manner. After that, connect the resistor to the sensor between contacts 7 and 8, opening a jumper between them. With a positive sign of Δr _β , R _β include in the shoulder of the strain gauge R ₄ , and with a negative sign of Δr _β , R _β include in the shoulder of the strain gauge R ₃ . Finally seal the sensor in normal climatic conditions.

 The validity of relation (3) can be shown as follows.

· ΔR_н (5) где ΔР_t - изменение давления во внутренней полости датчика от температуры;
Р_н - номинальное давление;
Δ R_н - абсолютное изменение сопротивления датчика, приведенное к одному плечу от воздействия давления. Изменение сопротивления термочувствительного резистора от температуры ΔR_βt компенсирующего изменение давления во внутренней полости датчика от температуры, будет равно
ΔR_βt=Δr_βα_βΔt, (6) где Δr_β - величина сопротивления термочувствительного резистора, на которую необходимо изменить термочувствительный резистор для компенсации изменения давления внутренней полости от температуры;
α_β - температурный коэффициент сопротивления материала термочувствительного резистора;
Δt - диапазон рабочих температур. Приняв выражения (5) и (6), получим: Δr_β·α_βΔt =

(7)
В соответствии с законом Шарля (см. Канкин Н.И., Ширкевич П.Г. Справочник по элементарной физике/M: Наука, 1966, с. 65)
ΔP_t= P_o·

· Δt (8) где Р_o - давление газа во внутренней полости датчика при нормальных климатических условиях. Величину ΔR_н определим из выражения U = U_пит·

· ε_r= U_пит·

·

(9) Отсюда, учитывая, что у реальных датчиков К = 1, найдем выражение для ΔR_н ΔR_н=

(10) Подставляя выражение (8) и (10) в (7), получим соотношение (3).The change in gas pressure in the internal cavity of the pressure sensor when exposed to temperature is similar to the change in pressure of the measured medium, but has the opposite direction. And, accordingly, since a change in the pressure of the external environment changes the resistance of the strain gauges, then a change in the gas pressure in the internal cavity of the sensor from temperature will lead to a similar change in the resistance of the strain gauge, but of the opposite sign. Thus, it is possible to compensate for the change in pressure in the internal cavity of the sensor by introducing an additional compensation resistor, the resistance of which depends on temperature. And since the strain gauge sensors have a thermosensitive resistor to compensate for changes in the initial output signal from the temperature, it is advisable to combine these sensors in one thermosensitive resistor, the value of which is determined as follows: when the pressure in the internal cavity of the sensor changes by ΔР _{t the} change of the strain gauge pressure sensor with a bridge measuring circuit will be
ΔR _t =

· ΔR _n (5) where ΔР _t is the change in pressure in the internal cavity of the sensor from temperature;
P _n - nominal pressure;
Δ R _n - the absolute change in the resistance of the sensor, reduced to one shoulder from the influence of pressure. The change in the resistance of the thermosensitive resistor to temperature ΔR _βt compensating for the change in pressure in the internal cavity of the sensor from temperature will be equal to
ΔR _βt = Δr _β α _β Δt, (6) where Δr _β is the resistance value of the heat-sensitive resistor, by which it is necessary to change the heat-sensitive resistor to compensate for changes in the pressure of the internal cavity from temperature;
α _β is the temperature coefficient of resistance of the material of the thermosensitive resistor;
Δt is the range of operating temperatures. Having accepted expressions (5) and (6), we obtain: Δr _β · α _β Δt =

(7)
In accordance with Charles's law (see Kankin NI, Shirkevich P.G. Handbook of elementary physics / M: Nauka, 1966, p. 65)
ΔP _t = P _o

· Δt (8) where P _o is the gas pressure in the internal cavity of the sensor under normal climatic conditions. The value of ΔR _{n is} determined from the expression U = U _pit

Ε _r = U _pit

·

(9) Hence, given that for real sensors K = 1, we find the expression for ΔR _n ΔR _n =

(10) Substituting expressions (8) and (10) in (7), we obtain relation (3).

 Using this method of temperature compensation of strain gauge sensors with a bridge measuring circuit, in comparison with existing methods, has the following advantages: increases the manufacturability of thermal compensation by providing the ability to measure the initial output signals of the sensor when exposed to test temperatures in an unpressurized state: it does not require complex and bulky sealing test equipment , which is made individually for each sensor; the time of measurement and testing is reduced, as well as the time of contact of the sensor with the medium being measured.

Claims (1)

METHOD FOR TEMPERATURE COMPENSATION OF TENSOR RESISTANCE SENSORS mainly with a bridge circuit, including operations for measuring the output signals of a strain gauge sensor at two temperatures from the operating range, calculating the parameters of a thermosensitive resistor, including it in a circuit of a bridge circuit and sealing the sensor housing, characterized in that, in order to improve manufacturability temperature compensation process, prior to sealing, measure the initial output signals of the strain gauge sensor, according to the results of the change s is corrected calculated value of the resistance temperature sensing resistor by an amount ΔR, defined by the relation

where U ₁ is the output voltage of the strain gauge sensor;
U ₂ - voltage supply of the strain gauge sensor;
R is the shoulder resistance of the bridge circuit;
P is the nominal measured pressure;
α is the temperature coefficient of the material of the thermosensitive resistor,
and then seal the strain gauge housing under normal climatic conditions.

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