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Devices for coolant temperature control in thermal stabilization systems of electronic equipment of transmitting devices

https://doi.org/10.38013/2542-0542-2020-3-29-37

Abstract

This article presents devices for controlling coolant temperature in thermal stabilization systems of electronic equipment. These are a thermal converter and a thermal relay realized on a Russian element base of the quality category “Voennaya Pryomka (Military Host)”. Experimental results for mock-up test samples are described along with their comparison with mass-produced analogues.

For citation:


Akhlestin K.V., Albutov A.N., Vasin A.Yu., Tsytsarev A.Yu., Fedorko K.I. Devices for coolant temperature control in thermal stabilization systems of electronic equipment of transmitting devices. Journal of «Almaz – Antey» Air and Space Defence Corporation. 2020;(3):29-37. https://doi.org/10.38013/2542-0542-2020-3-29-37

Introduction

At present, an element base nomenclature for development and construction of state-of-the-art systems for maintaining thermal regimes, in par­ticular, liquid thermal stabilisation systems, in the “Military Acceptance” (MA) quality category is close to non-existent. At the same time, customa­rily applied elements not always meet the con­temporary requirements to measurement accuracy and possibilities of signal transmission for digital processing. Thus, the basic disadvantages in ap­plication of thermal resistors with negative (posi­tive) temperature coefficient of resistance (TCR) is their limited temperature range, non-lineari­ty of the output response, and variation of their characteristics over time [1, 2]. Characteristic dependencies for two thermal resistor types are given in Fig. 1.

Application of digital microcircuits intended for installation on integrated circuit boards is associated with engineering complexity of their integration in a thermal stabilisation system for measuring coolant temperature in the hydraulic line.

The main requirement to a thermal stabili­sation system is keeping the coolant temperature within a specified range. In so doing, the measu­red temperature values are used in the control cell algorithm for switching functional devices on and off (heater and heat exchanger block fans), as well as for generating thermal stabilisation sys­tem readiness signal for switching a transmitting device on [3][4].

Hence, there is a need not only for upgra­ding the existing thermal stabilisation system pro­ducts so as to improve their characteristics, but also for developing new engineering solutions enabling to ensure the desired parameter measu­rement accuracy with account of contemporary requirements to digital control and monitoring in the thermal stabilisation system transmitting de­vice, as well as expanding the element base no­menclature in the “MA” quality category.

This paper presents the results of develop­ment and practical implementation of such de­vices as a thermal converter and a thermal relay, which collectively make it possible to improve overall reliability and efficiency of thermal stabi­lisation systems.

Schematic diagrams

A schematic electrical diagram of thermal con­verter is given in Fig. 2. The basic element is temperature-sensitive microcircuit 1019ChT3S (D1), which converts the temperature value into output current of 203...433 μΑ with temperature coefficient of 1 μA/°С at a measured medium temperature from minus 60 to 150 °С and supply voltage of 4...30 V. Thermal converter input power voltage of 28 V is supplied to reference voltage source (D2) and collector of transistor (VT1). The generated reference voltage of 12 V is supplied to operating amplifier (D3), which sets voltage at the transistor emitter depending on the difference of voltages supplied from the output of tempera­ture-sensitive microcircuit and voltage divider, from resistors R2 and R3. Precision resistor R1 shapes voltage proportionally to the temperature of the measured medium. As a result, the value of thermal converter’s circuit consumption current changes proportionally to the measured medium temperature value. Diode VD1 protects circuit elements against wrong polarity of the supplied power.

 Fig. 2. Electrical schematic diagram of thermal converter

Resistors R4, R5, and R7 control the am­plification factor of the operating amplifier for forming thermal converter’s current loop within a range of 10...24 mA. Trimmer resistor R* pro­vides current loop trimming for obtaining tem­perature measurement absolute error of ±1 °С. A mathematical model of the thermal converter is described by the expression:

where Iout(T) - circuit consumption current value, A; It(T) - temperature-sensitive microcircuit current value, A; R1, R2, R3, R4, R5, R7 - resistance values of resistors in the diagram circuits, Ω; R* - resistance value of trimmer resistor, Ω; UREF - voltage value of reference voltage source, V; Ic - consumption current value of thermal converter circuit elements, A.

 

A diagram of thermal converter connection to the control cell is given in Fig. 3. The generated thermal converter current produces voltage of 1.5...3.6 V on resistor RH = 150 Ω, which is measu­red by analogue-to-digital converter (ADC). Since the temperature value is converted into the value of current, measurements at the ADC output are not influenced by induced external interference and losses to the length of cables in case of signal transmission to large distances.

Fig. 3. Thermal relay connection diagram

An electrical schematic diagram of the thermal relay is given in Fig. 4. The diagram is implemented with the use of temperature-sensitive microcircuit 1019ChТ3S (D1). Thermal relay input power voltage of 28 V is supplied to reference voltage source (D2), temperature-sensitive microcircuit, and also to the second contact of connector XI via closed commutator (D3) switch. The reference voltage of 12 V is supplied to voltage comparator (D4) and voltage divider from resistors R2 and R3. The resistance values of these resistors are selected such that to make voltage comparator actuate when the value of temperature-sensitive microcircuit current corresponds to the measured medium temperature exceeding 90 °С. Voltage from the comparator output is supplied to the commutator, which opens the 28 V power supply circuit. The commutator on the base of microcircuit 2M419A1 allows commutation current up to 7 А. Trimmer resistor R* provides current loop trimming for obtaining temperature measurement absolute error of ±1 °С, and diode VD1 protects circuit elements against wrong polarity of the supplied power.

Fig. 4. Electrical schematic diagram of thermal relay

The resistance values of resistors R1, R2, and R3 depend on a required value of thermal relay (Trelay) actuation temperature and are defined by the following expression:

where IT.M.(Trelay) – value of temperature-sensitive microcircuit’s current at which thermal relay actuates, А; R1, R2, R3 – resistance values of resistors in the diagram circuits, Ω; R*– resistance value of trimmer resistor, Ω; UREF – voltage value of reference voltage source, V. In this way, the circuit design solutions described above, based on application of a temperature-sensitive microcircuit, ensure linear dependence of thermal converter’s current source on the measured medium temperature, as well as the specified temperature of thermal relay actuation.

The proposed circuit designs are simple from the construction viewpoint, which makes it possible to implement them on the modern domestic element base of the “MA” quality category.

Design

The thermal converter and thermal relay have a unified sealed-in design. A general view of the structure, with the basic elements and overall dimensions, is given in Fig. 5. The housing, cover, and union connection are made of aluminium alloy for better machining manufacturability of the workpieces. Sealing-in quality of the housing with a printed circuit board inside is provided by means of rubber gaskets for the cover and connector, and also by a sealing ring for the union. The printed circuit board is fixed in the mounting seats of the housing by screws with washers. The temperature-sensitive microcircuit is installed in the inner space of the union, in the point of contact with the measured medium, on heat-sink organosilicon adhesive sealant (Elasil 137-182) and suffused with two-component heat-resistant dielectric elastic sealing compound (Pentelast-711) for reliable fixing. Total thickness of the wall with
heat-sink coating in the temperature-sensitive microcircuit contact surface area does not exceed 1.2 mm. The design value of thermal resistivity in this case will amount to max. 1×10–3 (°С·m2 )/W [5]. Wires of MGTF type from the connector and temperature-sensitive microcircuit are soldered on the printed circuit board into via-holes. Since the printed circuit board with electronic components is inside the housing and has no direct contact with the measured medium, this precludes overheating of those components above the permissible working temperature of 125 °С.

Fig. 5. Unified design

 

The union for thermal converter and thermal relay mounting in the hydraulic line is designed for standard union connection М20*1.5 [6].

Application of connectors (housing socket for 3 or 4 pins) of 2RTT type, with similar over­all and connecting dimensions ensures protec­tion against wrong connection of power sup­ply to those devices in the thermal stabilisation system without a key. The housings also feature laser-etched decimal number and designation.

Experimental results

The experimental results of thermal converter mock-up sample operation, in comparison with an equivalent device TPU 0304/М1, serially pro­duced by NPP Elemer (Zelenograd) and having no “MA” quality category, are given in Fig. 6 in the form of current vs. air temperature dependence characteristics. The research was conducted in a heat and cold climatic chamber, with curing in each measured point until consumption current stabilisation.

Analysis of the research results showed that the values of thermal converter mock-up sample current, with air temperature varying, were pro­portional to the values of current of the equivalent sample, with the temperature coefficient equal to 0.12 mA/°C. The difference between current values of the mock-up sample and the equivalent sample made 6 mA across the entire range of the measured medium temperatures. This difference is explained by the consumption currents of thermal converter circuit elements. The difference can be compensated through correction of measurements in the micro­controller ADC or selection of resistance ratings of the thermal converter circuit resistors.

Hence, the obtained results confirm correct­ness of the proposed circuit design solutions for constructing a thermal converter circuit. A com­parative characteristic of the mock-up and equiv­alent sample is given in Table 1.

Table 1. Comparative characteristic of thermal converter and equivalent

A key requirement to the thermal relay is ac­tuation precision, since these relays are applied for protection of vacuum-tube microwave devices in the transmitter against impermissible overheating. The working temperature of the coolant in ther­mal stabilisation systems is within a range of 55...85 °С. Actuation of the transmitter protection against impermissible overheating is set for coolant temperature exceeding 90 °C [7].

The experimental results of thermal re­lay mock-up sample operation, in comparison with an equivalent device T35P-07 (as per TU 25.02.06.1995-76), are presented in Fig. 7 as a logic action vs. measured medium temperature characteristic.

Fig. 7. Thermal relay characteristics: а) Т35P-07, b) mock-up sample

The basic characteristic of the thermal re­lay is the width of a dead zone, i. e. the difference between the temperatures of relay actuation and release [8]. Temperature sensor relay T35P-07 has the dead zone width of max. 4 °С, with ±2 °C measurement allowance.

The experiment findings showed that the thermal relay mock-up sample had the dead zone width of max. 4 °С, occurring due to the existing thermal resistivity of the structure. A comparative characteristic of the mock-up and equivalent sample is given in Table 2.

Table 2. Comparative characteristic of thermal relay and equivalent

Conclusion

The paper presents the results of circuit design and engineering solutions, as well as the experimental data for two devices: thermal con­verter and thermal relay. The thermal converter has measurement accuracy comparable with that of a serially produced equivalent across the entire range of coolant temperature values. The thermal relay has actuation precision characteristics no worse than those of an equivalent. Notably, the proposed devices are implemented on the modern domestic element base of the “MA” quality cate­gory and tested using test bench equipment of the transmitter thermal stabilisation system.

References

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About the Authors

K. V. Akhlestin
NPO Almaz named after A. A. Raspletin, JSC
Russian Federation

Akhlestin Kirill Vladimirovich - Engineer of the 2nd category. Research interests: radio transmitter and receiving equipment for ground and on-board microwave devices.

Moscow



A. N. Albutov
NPO Almaz named after A. A. Raspletin, JSC
Russian Federation

Albutov Aleksandr Nikolaevich - Departmental Head. Research interests: radio transmitter and receiving equipment for ground and on-board microwave devices.

Moscow



A. Yu. Vasin
NPO Almaz named after A. A. Raspletin, JSC
Russian Federation

Vasin Andrey Yurievich - Engineer of the 2nd category. Research interests: radio transmitter and receiving equipment for ground and on-board microwave devices.

Moscow



A. Yu. Tsytsarev
NPO Almaz named after A. A. Raspletin, JSC
Russian Federation

Tsytsarev Alexey Yurievich - Cand. Sci. (Engineering), Deputy Head of the Special Design Bureau. Research interests: radio transmitter and receiving equipment for ground and on-board microwave devices.

Moscow



K. I. Fedorko
NPO Almaz named after A. A. Raspletin, JSC
Russian Federation

Fedorko Konstantin Igorevich - Engineer of the 2nd category. Research interests: radio transmitter and receiving equipment for ground and on-board microwave devices.

Moscow



Review

For citation:


Akhlestin K.V., Albutov A.N., Vasin A.Yu., Tsytsarev A.Yu., Fedorko K.I. Devices for coolant temperature control in thermal stabilization systems of electronic equipment of transmitting devices. Journal of «Almaz – Antey» Air and Space Defence Corporation. 2020;(3):29-37. https://doi.org/10.38013/2542-0542-2020-3-29-37

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ISSN 2542-0542 (Print)