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SCTB ElPA Ltd. (special engineering and design bureau of electronics, instrument-making and automation) is an assign of Uglich branch of NIIChasprom, established in 1959 on the Uglich watch plant Chaika territory for applied science and production consolidation. On the last 28 years SCTB ElPA specializes in manufacture and R&D of quartz resonant devices.


Compensation algorithms Temperature effect in quartz pressure and temperature transmitters.

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Manometric feature of quartz resonators is the reproducibility of temperature-frequency characteristic (PMx), which must be compensated with high accuracy over a wide temperature range and in the range of operating pressures. You must take into account the change in the temperature sensitivity of the cavity of the pressure acting on it. The following describes two methods of temperature compensation.


Algorithm № 1


The best way - is the calculation of pressure on the regression function of two factors: the temperature and pressure. Below are two functions of degree and communication factors are sufficient for the calculation of pressure with the required accuracy.
Recommended for inverters with a permissible additional error over the full operating temperature range from 0.03% to 0.15%.
Regression function is represented by a polynomial of the form 



Р= A0+A1(F(t)-F(t0))+A2(F(t)-F(t0))2+A3(F(p)-F(p0))+A4(F(p)-F(p0))2+A5(F(t)-F(t0)) x (F(p)-F(p0))+ A6(F(t)-F(t0))2 x (F(p)-F(p0))+A7(F(t)-F(t0)) x (F(p)-F(p0))2+ A8(F(t)-F(t0))2 x (F(p)-F(p0))2


F (t)-frequency channel with temperature;
F (t0)-constant component temperature channel;
F (p)-frequency channel with pressure;
F (p0)-constant component of the channel pressure;
A0 ... A8 are the coefficients of the regression function


Example calibration protocol converter.

Пример протокола калибровки преобразователя

Коэффициенты полинома


Algorithm number 2
Since quartz resonators manometric changes in the frequency dependence of the temperature is much lower than that of sensitive semiconductor elements for applications where a narrow operating temperature range (up to + 30 ° C), operating pressure range of not more than 60% of the full pressure and is admissible additional temperature error of 0.1% (in the operating temperature range). Can be neglected factor tilting, BCH, depending on temperature and assume that the BCH is shifted in parallel. Algorithm for calculating the pressure-compensated additional temperature error below.
In particular, the temperature error compensation method is proposed for converters PDTK ,1-0-2-R is not in plastic sealed boxes, so that they have a lower cost compared to the converters in a sealed metal case.


Algorithm and formulas for calculating the pressure


1. For the temperature:


T=T0+B1(F(t)-F0(t))+B2(F(t)- F0(t))2+B3(F(t)- F0(t))3                                                                                    [1],

-T 0 is the temperature at which the sensor outputs frequency F (t) 0;
-B 1, B 2, B 3 - approximation coefficients of T (f) 0.

2. Pressure sensor:


Р=Р0+A1(Fтк-F0(p))+A2(Fтк- F0(p))2+A3(Fтк- F0(p))3                                                                                                         [2],


- P 0 is the pressure at which the pressure sensor outputs frequency F0 (p) at a temperature T 0
- A 1, A 2, A 3 - coefficients of the approximation of the function F (f);
Ftk = F (p) - Δf [3]
where F mk - the frequency with pressure sensor with temperature compensation;
F (p)-frequency measured with a pressure sensor, without temperature compensation;
Δf - correction, compensating for the pressure sensor drift due to temperature, Hz
Δf = k 1 (T-T 0) + k 2 (T-T 0) 2 [4]
T is the temperature at which the pressure is measured F (p), which is calculated by the formula [1];
T0 - the temperature at which there is no temperature correction (F TC = F (p)), which was filmed at BCH (indicated in the passport);
k 1, k 2 - coeff. approximation of Fp (t) BTH defined in the range of operating temperatures.


The general formula for calculating the pressure with temperature compensation:

Р=Р0+A1[F(p) – (k1(Т-Т0)+k2(Т-Т0)2) - F0(p)]+A2[F(p) – ( k1(Т-Т0)+k2(Т-Т0)2) - F0(p)]2+A3[F(p) – ( k1(Т-Т0)+k2(Т-Т0)2) - F0(p)]3

Note. Use 1st algorithm compared with the 2nd is more accurate and allows for compensation in a wide range of pressures and temperatures. But the calibration for the 1st algorithm more time-consuming and costly than the calibration for the 2nd of the algorithm as necessary condition for tightness of the housing drive or volume, plus the actual number of pixels in the calibration for the 1st algorithm more than the calibration for the 2nd algorithm. 


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