Design of periscope protective glass control system based on temperature sensor AD590M

In order to prevent seawater from entering the interior of the periscope, there is a protective glass that can withstand a certain amount of seawater static pressure at the light entrance of the periscope. When a submarine uses a periscope to observe in cold climates, its head window can quickly be covered with condensed frost, and the only solution in the past was to lower the periscope, rinse it in seawater, and raise it to observe. However, this method is neither convenient nor ideal, because it is covered again shortly after rising. In extremely cold climates, such as when used in the Arctic Ocean, the periscope can be severely affected and rendered useless.The solution to the above problem is to set the head in the periscope

Overview

In order to prevent seawater from entering the interior of the periscope, there is a protective glass that can withstand a certain amount of seawater static pressure at the light entrance of the periscope. When a submarine uses a periscope to observe in cold climates, its head window can quickly be covered with condensed frost, and the only solution in the past was to lower the periscope, rinse it in seawater, and raise it to observe. However, this method is neither convenient nor ideal, because it is covered again shortly after rising. In extremely cold climates, such as when used in the Arctic Ocean, the periscope can be severely affected and rendered useless. The solution to the above problems is to set the head protection glass heating device in the periscope, and its function is to provide deicing, defrosting and defogging for the protective glass of the submarine periscope window, so as to ensure the normal use of the periscope.

temperature control system

The temperature control system consists of a heated conductive film on the protective glass of the periscope window, a temperature sensor and a control circuit. The average temperature of the protective glass of the window is measured by two temperature sensors AD590M on the diagonal of the window glass, and the output current of the sensor is converted into a voltage through the temperature detection circuit, which is compared with the threshold voltage of the double-limit voltage comparator to Display the actual temperature of the protective glass. Scope and control the work of the relay, through the conversion of the working mode of the normally closed and normally open contacts of each relay, the control of the electric heating of the conductive film of the window protection glass is realized.

Conductive film

A transparent conductive film is plated on the protective glass of the periscope window, metal electrodes are plated on the periphery of the conductive film, temperature sensors are bonded to the four corners of the window protective glass, and the heating temperature control device passes through the metal electrodes around the film to conduct electricity. The film applies voltage-controlled AC power to heat the protective glass of the periscope window. Since the conductive film is always exposed to the air, the film layer is susceptible to damage and dust. After electrification, the violent movement of free electrons in the conductive film is accelerated, converting electrical energy into heat energy and heating the protective glass. . If the heating temperature is too high and the time is too long, the speckled film will fall off, short circuit or even breakdown. If the heating temperature is too low and the time is too short, the purpose of rapid deicing, defrosting and defogging cannot be achieved. To solve this contradiction, in addition to properly selecting the power of the heating device, it is very necessary to automatically adjust and monitor the heating temperature to meet the requirements of heating at different external temperatures.

Choice of temperature sensor

There are two main types of semiconductor temperature sensors: digital temperature sensors and analog temperature sensors, and each type includes many kinds of products. With functions such as monitoring local and remote temperature, digital temperature sensors have replaced analog output temperature sensors in many applications. However, the analog temperature sensor can generate a voltage or current signal that is linearly proportional to the temperature, and no additional linearization circuit is required to calibrate the nonlinearity of the sensor, so the analog output temperature sensor also has a wide range of applications without digital output. Such as AD590M current output temperature sensor.

AD590M is a monolithic integrated two-terminal current output temperature sensor produced by American Analog Devices. Its working voltage is 4~30V; the temperature measurement range is -55~150℃; the accuracy is ±0.5℃; it has a standardized output and an inherent linear relationship (When the temperature changes by 1°C, the output current changes by 1mA); the output zero point is the zero point of the thermodynamic temperature scale, that is, the output current of the AD590M is 0mA at -273°C, and the output current is about 273mA at 0°C. Its high-impedance current output makes it insensitive to voltage drops over long lines, making it useful for remote temperature sensing.

Window glass temperature measurement and control circuit

The periscope window glass temperature control circuit is shown in Figure 1.

 Design of periscope protective glass control system based on temperature sensor AD590M

Figure 1 Window glass temperature measurement control circuit

In order to accurately measure the temperature of the protective glass, two of the four sensors AD590M on the diagonal line of the four sensors on the inner side of the window glass are connected in parallel, and the other two are reserved to form a circuit for measuring the average temperature. The design of the temperature measurement circuit first needs to convert the current into voltage. Since the current output element AD590M has a corresponding relationship between the current and the temperature of 1μA/K, the resistor R1=10kΩ/2=5kΩ is selected, and the voltage drop on this resistor is about 10mv, That is, it is converted into 10mv/k, and the capacitor C is used to filter out the noise.

The two ends of the relay coil are respectively connected to the power supply voltage and the c-pole of the output transistor. When the current flowing through the relay coil suddenly decreases, an electromotive force will be induced at both ends, which is superimposed with the original power supply voltage and added to the output. In order to eliminate the harmful effects of the induced electromotive force, a diode is connected in parallel next to the relay to absorb the induced potential and protect the transistor.

The operational amplifier A1 is connected as a voltage follower to increase the input impedance of the signal. A2 and A3 form a window comparator, the non-inverting input terminal of comparator A2 is connected to the upper threshold Vh of the window, the inverting input terminal of comparator A3 is connected to the lower threshold Vl of the window, and the input signal Vi is simultaneously added to the non-inverting threshold of comparator A2 input and the inverting input of comparator A3.

When Vi < Vl, A2 output is high level, transistors VT2, VT3, diode D4 are off, relays KA2, KA3 are de-energized and released; A3 output is low level, VT1, D5 are on, and the relay connected to transistor VT1 KA1 is energized and closed, and the normally open contact KA1-1 is closed. The 220V AC power supply passes through the step-down transformer T through the normally closed contact KA3-1 of the relay KA3 to energize and heat the conductive film on the protective glass, and the indicator LED1 lights up.

When Vl

At the same time, the normally open contact KA2-2 of the relay KA2 is closed, and the relay timer KA4 is energized and closed, and after the delay heating for 5 minutes (the delay heating time can be adjusted within the range of 0.1 seconds to 10 minutes as needed) ), the normally closed contact KA4-1 of KA4 is disconnected, and the heating of the conductive film is stopped.

KA4 is a multi-function relay timer H3RN-1, with on-delay, interval, flashing off-start and flashing on-start 4 working modes; the timing range is 0.1 seconds to 10 minutes; the control output is SPDT form; rated power supply voltage is DC 12V, 24V, AC 24V; rated current 3A resistive load.

When Vi > Vh, A3 output is high level, VT1, D5 are off, A2 output is low level, VT2 is off, VT3, D4 are on, and the relay KA3 connected to VT3 is energized and closed, KA3 is normally closed The contact KA3-1 is disconnected, the conductive film on the protective glass is not energized and heated, and the indicator LED3 is on.

debugging

In order to reduce the influence of self-heating of the current output type temperature sensor AD590M, a lower excitation voltage should be used. Therefore, the output voltage of the three-terminal voltage regulator LM7805C is used as the excitation voltage of the AD590M, and this voltage is used as the upper and lower threshold levels of the comparator at the same time. The reference voltages of Vh and Hl can overcome the influence of power supply fluctuations on the upper and lower threshold levels Vh and Hl, thereby improving the temperature measurement accuracy. When adjusting, use an infrared thermometer to measure the temperature of the surface of the protective glass, and use a digital multimeter to measure the corresponding output voltage. When the temperature is 10°C, the measured output voltage is used as the lower threshold level Hl. When the temperature is 30°C , the measured output voltage is used as the upper threshold level Vh, repeated several times, and the average value of the upper and lower threshold levels Vh and Hl is taken to determine Vh and Hl.

Epilogue

The protective glass temperature control system uses the analog temperature sensor AD590M. The circuit designed by AD590M is simple in structure, reliable in operation and convenient in debugging. Flat Vh, Hl) wide, in the case that the temperature around the periscope window is high and only needs to be defogged, it has outstanding practical advantages, so it has practical application value for the temperature detection system that requires long line transmission for the periscope protective glass.

The Links:   LM150X05-C2 LTM150X0-L01