Temperature is one of the most basic physical quantities in science and technology. In industrial production, temperature is often one of the most important parameters for characterizing objects and process states. In the medical field, body temperature is also the medical parameter we are most concerned about. Figure 1 Internal structure of the DS18B20 Figure 2 DS18B20 outline and pinout Based on the above characteristics, the DS18B2 makes the hardware consumption less, the system design is more flexible and convenient, the price is cheaper, and the volume is smaller. A ball check valve is a check valve in which the closing member, the movable part to block the flow, is a spherical ball. In some ball check Valves, the ball is spring-loaded to help keep it shut. For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal. The interior surface of the main seats of ball check valves are more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow. Check Valves, Water Check Valves, Brass Check Valves, Sanitary Check Valves ZHEJIANG KINGSIR VALVE CO., LTD. , https://www.kingsirvalves.com
With the development of modern technology, temperature measurement has become more and more widely used in various fields, and temperature measurement technology has also been paid attention to by people. The multi-function temperature measuring instrument is a typical example. Using the single-chip technology, it is developing in the direction of digitization and intelligence. Here, a multi-function temperature measuring instrument can be introduced, which can measure the ambient temperature and measure the temperature of the human body, achieve fast response, digital display temperature value, and have the purpose of high temperature alarm.
1 hardware circuit design
1. 1 The temperature sensor uses DA LLAS temperature sensor DS18B20 as the temperature acquisition device. The internal structure of DS18B20 is mainly composed of 64-bit ROM, temperature sensitive component, internal memory and configuration register, as shown in Figure 1.
(1) 64-bit ROM. Its content is a 64-bit serial number, which can be regarded as the address sequence code of the DS18B20. Its function is to make each DS18B20 different, so that multiple DS18B20s can be connected to one bus.
(2) Temperature sensitive components. It completes the measurement of the temperature and the measured results are stored in two 8 b temperature registers.
(3) Internal memory. The internal memory includes a scratchpad RAM and a nonvolatile, electrically erasable E2 PROM that holds the high and low temperature triggers TH, TL and configuration registers. 
The DS18B20 has the following features:
(1) The unique single-wire interface mode requires only one port line when connected to the MCU; (2) The temperature measurement range is -55~ + 125°C, and the accuracy is ±0. 5 °C in the range of -10~ + 85°C; (3) 9~12 digits digital reading mode can be realized by programming; (4) User can set non-volatile alarm upper and lower limit values; (5) Peripheral circuit is simple, no external components are needed for use, available data Bus-powered, voltage range is 3. 0 ~ 5. 5 V No backup power supply required; (6) DS18B20 has TO 92, SOIC and CSP packages. The shape and pin arrangement of DS18B20 are selected as shown in Figure 2, where VDD For the external power supply input, GND is the common ground and DQ is the digital signal output. 
Ball check valves are often very small, simple, and cheap. They are commonly used in liquid or gel minipump dispenser spigots, spray devices, some rubber bulbs for pumping air, etc., manual air pumps and some other pumps, and refillable dispensing syringes. Although the balls are most often made of metal, they can be made of other materials, or in some specialized cases out of artificial ruby. High pressure HPLC pumps and similar applications commonly use small inlet and outlet ball check valves with both balls and seats made of artificial ruby, for both hardness and chemical resistance. After prolonged use, such check valves can eventually wear out or the seat can develop a crack, requiring replacement. Therefore, such valves are made to be replaceable, sometimes placed in a small plastic body tightly-fitted inside a metal fitting which can withstand high pressure and which is screwed into the pump head.
There are similar check valves where the disc is not a ball, but some other shape, such as a poppet energized by a spring. Ball check valves should not be confused with Ball Valves, which is a different type of valve in which a ball acts as a controllable rotor to stop or direct flow.
A diaphragm check valve uses a flexing rubber diaphragm positioned to create a normally-closed valve. Pressure on the upstream side must be greater than the pressure on the downstream side by a certain amount, known as the pressure differential, for the check valve to open allowing flow. Once positive pressure stops, the diaphragm automatically flexes back to its original closed position.
A swing check valve or tilting disc check valve is check valve in which the disc, the movable part to block the flow, swings on a hinge or trunnion, either onto the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle. Although swing check valves can come in various sizes, large check valves are often swing check valves. The flapper valve in a flush-toilet mechanism is an example of this type of valve. Tank pressure holding it closed is overcome by manual lift of the flapper. It then remains open until the tank Drains and the flapper falls due to gravity. Another variation of this mechanism is the clapper valve, used in applications such firefighting and fire life safety systems. A hinged gate only remains open in the inflowing direction. The clapper valve often also has a spring that keeps the gate shut when there is no forward pressure. Another example is the backwater valve (for sanitary drainage system) that protects against flooding caused by return flow of sewage waters. Such risk occurs most often in sanitary drainage systems connected to combined sewerage systems and in rainwater drainage systems. It may be caused by intense rainfall, thaw or flood.
A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. In addition to closing in response to backflow or insufficient forward pressure (normal check-valve behavior), it can also be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure.
A lift-check valve is a check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly. When the pressure is no longer higher, gravity or higher downstream pressure will cause the disc to lower onto its seat, shutting the valve to stop reverse flow.
An in-line check valve is a check valve similar to the lift check valve. However, this valve generally has a spring that will 'lift' when there is pressure on the upstream side of the valve. The pressure needed on the upstream side of the valve to overcome the spring tension is called the 'cracking pressure'. When the pressure going through the valve goes below the cracking pressure, the spring will close the valve to prevent back-flow in the process.
A duckbill valve is a check valve in which flow proceeds through a soft tube that protrudes into the downstream side. Back-pressure collapses this tube, cutting off flow.
A pneumatic non-return valve.
Multiple check valves can be connected in series. For example, a double check valve is often used as a backflow prevention device to keep potentially contaminated water from siphoning back into municipal water supply lines. There are also double ball check valves in which there are two ball/seat combinations sequentially in the same body to ensure positive leak-tight shutoff when blocking reverse flow; and piston check valves, wafer check valves, and ball-and-cone check valves.