DS18B20传感器技术详解：1-Wire通信与温度监控

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"DS18B20是一款独特的数字温度传感器，以其1-Wire通信接口而闻名，只需一个端口即可实现通信。每个设备都内置了一个唯一的64位序列码，便于识别和管理。该传感器支持多滴模式，适用于分布式温度传感应用，无需额外组件，简化了系统设计。传感器的工作电源范围在3.0V到5.5V之间，能够测量从-55°C到+125°C的温度范围，尤其在-10°C至+85°C时具有0.5°C的精度。用户可以根据需求选择9到12位的温度分辨率。DS18B20能在750毫秒内将温度转换为12位数字值。此外，它还允许用户定义非易失性（NV）报警设置，当温度超出预设范围时，通过报警搜索命令能快速定位并处理异常设备。该传感器有8-pin SO、8-pin SOP和3-pin TO-92三种封装形式，并与DS1822软件兼容，广泛应用于恒温控制、工业系统、消费产品、温度计等各种热敏系统。" DS18B20传感器是 Dallas Semiconductor (现 Maxim Integrated) 生产的一款高性能数字温度传感器。其主要特性包括： 1. **1-Wire接口**：这种接口只需要一根数据线（DQ）就能实现通信，极大地减少了硬件接口的需求，降低了布线复杂性。 2. **唯一序列码**：每个DS18B20传感器都有一个唯一的64位序列码，存储在非易失性ROM中，这使得在多个传感器共存的系统中可以方便地识别和管理各个传感器。 3. **多滴模式**：允许多个DS18B20传感器连接到同一根数据线上，简化了分布式温度监测系统的构建。 4. **电源管理**：传感器可以从数据线上获取电源，工作电压范围宽，从3.0V到5.5V，这为应用提供了更大的灵活性。 5. **温度测量**：DS18B20的温度测量范围广，从-55°C到+125°C，在特定范围内（-10°C到+85°C）精度可达0.5°C，满足大多数环境监控需求。 6. **可选分辨率**：用户可以根据实际需求，设置温度分辨率在9位到12位之间，以平衡精度和转换速度。 7. **快速转换**：传感器能够在750毫秒内完成一次温度转换，转换为12位数字值，提供实时温度信息。 8. **报警功能**：具备用户定义的非易失性报警设置，当温度超出设定的上限或下限时，能够触发报警，帮助用户及时发现并处理温度异常。 9. **封装形式**：DS18B20提供不同封装选择，包括8-pin SO、8-pin SOP和3-pin TO-92，适应不同应用场景的需求。 10. **软件兼容性**：与DS1822软件兼容，意味着已有的DS1822系统可以轻松升级到DS18B20，减少了开发成本。这款传感器广泛应用于各种领域，如暖通空调系统的温度控制、工业过程监控、智能家居设备、户外气象站以及医疗设备等，它的高精度和易于集成的特性使其成为数字温度测量的理想选择。

DS18B20

4 of 20

OPERATION — ALARM SIGNALING

After the DS18B20 performs a temperature conversion, the temperature value is compared to the user-

defined two’s complement alarm trigger values stored in the 1-byte T

and T

registers (see Figure 3).

The sign bit (S)

indicates if the value is positive or negative: for positive numbers S = 0 and for negative

numbers S = 1. The T

and T

registers are nonvolatile (EEPROM) so they will retain data when the

device is powered down. T

and T

can be accessed through bytes 2 and 3 of the scratchpad as explained

in the MEMORY section of this datasheet.

AND T

bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0

Only bits 11 through 4 of the temperature register are used in the T

and T

comparison since T

and T

are 8-bit registers. If the measured temperature is lower than or equal to T

or higher than T

, an alarm

condition exists and an alarm flag is set inside the DS18B20. This flag is updated after every temperature

measurement; therefore, if the alarm condition goes away, the flag will be turned off after the next

temperature conversion.

The master device can check the alarm flag status of all DS18B20s on the bus by issuing an Alarm Search

[ECh] command. Any DS18B20s with a set alarm flag will respond to the command, so the master can

determine exactly which DS18B20s have experienced an alarm condition. If an alarm condition exists

and the T

or T

settings have changed, another temperature conversion should be done to validate the

alarm condition.

POWERING THE DS18B20

The DS18B20 can be powered by an external supply on the V

pin, or it can operate in “parasite power”

mode, which allows the DS18B20 to function without a local external supply. Parasite power is very

useful for applications that require remote temperature sensing or that are very space constrained. Figure

1 shows the DS18B20’s parasite-power control circuitry, which “steals” power from the 1-Wire bus via

the DQ pin when the bus is high. The stolen charge powers the DS18B20 while the bus is high, and some

of the charge is stored on the parasite power capacitor (C

) to provide power when the bus is low. When

the DS18B20 is used in parasite power mode, the V

pin must be connected to ground.

In parasite power mode, the 1-Wire bus and C

can provide sufficient current to the DS18B20 for most

operations as long as the specified timing and voltage requirements are met (refer to the DC

ELECTRICAL CHARACTERISTICS and the AC ELECTRICAL CHARACTERISTICS sections of this data

sheet). However, when the DS18B20 is performing temperature conversions or copying data from the

scratchpad memory to EEPROM, the operating current can be as high as 1.5mA. This current can cause

an unacceptable voltage drop across the weak 1-Wire pullup resistor and is more current than can be

supplied by C

. To assure that the DS18B20 has sufficient supply current, it is necessary to provide a

strong pullup on the 1-Wire bus whenever temperature conversions are taking place or data is being

copied from the scratchpad to EEPROM. This can be accomplished by using a MOSFET to pull the bus

directly to the rail as shown in Figure 4. The 1-Wire bus must be switched to the strong pullup within

10ms (max) after a Convert T [44h] or Copy Scratchpad [48h] command is issued, and the bus must be

held high by the pullup for the duration of the conversion (t

conv

) or data transfer (t

= 10ms). No other

activity can take place on the 1-Wire bus while the pullup is enabled.

The DS18B20 can also be powered by the conventional method of connecting an external power supply

to the V

pin, as shown in Figure 5. The advantage of this method is that the MOSFET pullup is not

required, and the 1-Wire bus is free to carry other traffic during the temperature conversion time.

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