Y.А.Vaskov, Е.G.Savchenko, V.М. Stuchebnikov

LLC MIDAUS, Ulyanovsk, Russia

Since 2019, Industrial Group MIDA has been producing standard transducers for absolute, gage pressure, vacuum, gage pressure-vacuum with 0.05% accuracy. For use in vacuum technology, a standard absolute pressure transducer MIDA-DA-15-S with flange connection KF25 has been developed (Fig. 1, 2).

The high-accuracy pressure transducer for vacuum equipment use piezoresistive sensor based on heteroepitaxial structures "silicon on sapphire", which ensures high accuracy, stability and reliability of devices [1]. These transducers provide a total error of <0.05% in the temperature range from +10 °С to +40 °С [2]. Correction of non-linearity and temperature error is carried out in the electronic unit of the sensor, with the piezoresistive bridge acting as the thermally sensitive element, thus removing the problem of temperature equality of the sensor and the thermosensitive element. Setting and subsequent reading of the measurement results is carried out via RS-485 interface. Modbus protocol is used to interact with transducers.

Fig. 1. Standard absolute pressure transducer MIDA-DA-15-S with KF25 flange.

These transducers have high operation speed, achieved by the use of a high-performance microcontroller and high-speed ADC. So, the minimum measurement time (from the moment the command is received by the sensor till the moment the message with the result is issued) for  MIDA-15 sensors is 25 ms. The maximum response time depends on such settings as the number of averaging points, the use of a hardware filter, and the length of the measurement interval. The resolution of the sensor was improved to 0.3 Pa compared with a resolution of about 2 Pa for earlier devices [2].

Fig. 2. MIDA-SA-15-S pressure transducer with a clamp for connection to a vacuum system.

These transducers are included in the register of measuring instruments of the Russian Federation. At the end of 2019, the accreditation of the metrological service of LLC MIDAUS was expanded, and now the company has the right to independent primary and periodic calibration of pressure instruments of the 0.05% accuracy.

In the research laboratory of IG MIDA, MIDA-SA-15-S transducers with pressure range of 100 kPa were compared to a 1st category standard absolute pressure gauge MPA-15 (Fig. 3). Typical test results are shown in the table. In parentheses is the certified error of MPA-15 measurement.

The results of the comparison of the MIDA-DA-15-S pressure transducer with MPA-15 pressure standard.

As can be seen from the table, the deviations of the transducer’s readings from the MPA-15 data are actually within the measurement error of the standard itself. To identify the real characteristics of the MIDA-SA-15-S transducer, it is necessary to compare it to a pressure standard of a higher class, especially in the low pressure range. The sensitivity threshold of the transducer is at the “noise” level of the ADC and is about 0.3 Pa (2.2×10^-3 mm Hg).

Fig. 3. The calibration system of absolute pressure transducers, based on the MPA-15 pressure standard.

Such results were achieved by optimization of the design and production technology of piezoresistibe sensors for these transducers, as well as by the transition to higher-resolution ADCs (24bit instead of 16bit). The obtained characteristics allow the use of these sensors as a standard of the first category.

MIDA-SA-15-S transducers can also be used as digital pressure gauges when connected to a computer with a Windows operating system or to a smartphone with an Android operating system via a USB adapter. The operation of the sensor and the recording of readings are performed using MIDA software [3]. Sensors can be certified as standards of the 1st or 2nd category.

Fig. 3. MIDA software [3] for setting up and working with sensors.

Nowadays, MIDA-SA-15-S transducers have successfully passed a preliminary test to control the vacuum in a thermal vacuum chamber and are operated by one of our customers (ST&KS LLC).

List of sources

[1]     Stuchebnikov V.M. Silicon-on-Sapphire structures as a material for piezoresistive mechanical transducers – Journal of Communication Technology & Electronics, Vol.50, No 6, 2005, pp. 622-637.

[2]     Vaskov Y.A., Savchenko E.G., Stuchebnikov V.M. MIDA-SA-15-S high-precision absolute pressure sensors based on Sapphire on  Silicon Structures // Vacuum Engineering and Technology - 2019. Proceedings of the 26th All-Russian Scientific and Technical Conference, St. Petersburg. 2019.S. 48-50.(In Russian).

[3]    MIDA Software