📚 Components of an Electronic Sensing System | 电子传感系统的组成部分
An electronic sensing system detects a physical quantity, converts it into an electrical signal, processes that signal, and then produces a useful output or action. In CIE A-Level Physics, you should be able to identify the main blocks of such a system and explain how each block contributes to the overall function, especially when a sensor is used with a potential divider and an operational amplifier.
电子传感系统检测一个物理量，将其转换为电信号，处理该信号，然后产生有用的输出或动作。在 CIE A-Level 物理中，你应该能够识别这种系统的主要模块，并解释每个模块如何对整体功能作出贡献，特别是当传感器与分压器和运算放大器一起使用时。
1. Block Diagram of a Sensing System | 传感系统框图
A general electronic sensing system can be represented by the sequence: physical input, sensor, signal conditioning, processing, and output device. Some systems also include feedback, which compares the output with a desired value and adjusts the input automatically.
一个通用的电子传感系统可以用以下顺序表示：物理输入、传感器、信号调理、处理以及输出设备。有些系统还包含反馈，即将输出与期望值进行比较，并自动调整输入。
An open-loop system has no feedback, so the output does not affect the input. A closed-loop system uses feedback to reduce error, making the system more accurate and stable.
开环系统没有反馈，因此输出不会影响输入。闭环系统利用反馈来减小误差，使系统更加准确和稳定。
The sensor is always the first active element because it must respond to the environmental change. The processing block may be analogue, digital, or a combination of both.
传感器始终是第一个有源元件，因为它必须对环境变化作出响应。处理模块可以是模拟的、数字的，或者两者的组合。
2. Sensors and Transducers | 传感器与换能器
A sensor is a device that detects a change in a physical quantity. A transducer is a device that converts energy from one form to another; therefore, an input transducer converts a non-electrical quantity into an electrical signal.
传感器是检测物理量变化的装置。换能器是将能量从一种形式转换为另一种形式的装置；因此，输入换能器将非电量转换为电信号。
For example, a thermistor is a temperature sensor and also a transducer because it converts a temperature change into a change in resistance. A microphone converts sound pressure variations into a varying voltage.
例如，热敏电阻是一种温度传感器，也是一种换能器，因为它将温度变化转换为电阻变化。麦克风将声压变化转换为变化的电压。
Passive sensors require an external power supply to produce a measurable output, such as an LDR in a potential divider. Active sensors generate their own voltage, such as a piezoelectric crystal under stress or a thermocouple.
无源传感器需要外部电源才能产生可测量的输出，例如分压器中的光敏电阻。有源传感器能自身产生电压，例如受压的压电晶体或热电偶。
In an electronic sensing system, the sensor is usually connected to a signal conditioning circuit so that its small resistance or voltage change can be converted into a larger and more usable signal.
在电子传感系统中，传感器通常连接到信号调理电路，以便将其微小的电阻或电压变化转换为更大且更可用的信号。
3. Common Input Sensors | 常见输入传感器
The table below summarises four common sensors used in CIE A-Level Physics. Each sensor changes resistance or generates a voltage in response to a physical quantity.
下表总结了 CIE A-Level 物理中常用的四种传感器。每种传感器都会根据物理量改变电阻或产生电压。
| Sensor | Physical quantity | Typical behaviour |
|---|---|---|
| LDR | Light intensity | Resistance decreases as light intensity increases |
| NTC thermistor | Temperature | Resistance decreases as temperature increases |
| Strain gauge | Strain or force | Resistance increases when stretched |
| Piezoelectric sensor | Pressure or vibration | Generates a p.d. when deformed |
These sensors rarely produce a large enough signal on their own. They are usually placed in a potential divider circuit so that the output voltage changes in a predictable way with the physical quantity.
这些传感器很少能单独产生足够大的信号。它们通常被放置在分压电路中，使输出电压以可预测的方式随物理量变化。
When a sensor is used in a potential divider, the output voltage depends on the ratio of the sensor resistance to the fixed resistance. This allows the sensing system to convert a resistance change into a voltage change.
当传感器用于分压器时，输出电压取决于传感器电阻与固定电阻的比值。这使传感系统能够将电阻变化转换为电压变化。
4. Signal Conditioning | 信号调理
Signal conditioning is the stage that modifies the raw sensor signal into a form suitable for further processing or display. It can include amplification, filtering, impedance matching, and linearisation.
信号调理是将原始传感器信号修改为适合进一步处理或显示的形式的阶段。它可以包括放大、滤波、阻抗匹配和线性化。
Amplification increases the amplitude of a small sensor voltage. A non-inverting operational amplifier with a gain of 1 + R_f/R₁ is often used for this purpose, where R_f is the feedback resistor and R₁ is the input resistor.
放大增加了小传感器电压的幅度。为此通常使用同相运算放大器，其增益为 1 + R_f/R₁，其中 R_f 是反馈电阻，R₁ 是输入电阻。
Filtering removes unwanted noise or interference. A low-pass filter removes high-frequency noise, while a high-pass filter removes slow drift or DC offsets in some applications.
滤波可以去除不需要的噪声或干扰。低通滤波器去除高频噪声，而在某些应用中高通滤波器去除缓慢漂移或直流偏移。
Impedance matching ensures that the sensor signal is not significantly reduced when connected to the next stage. A buffer amplifier with high input impedance and low output impedance is often used for this purpose.
阻抗匹配确保传感器信号在连接到下一级时不会被显著衰减。为此通常使用具有高输入阻抗和低输出阻抗的缓冲放大器。
5. Voltage Divider Circuits for Sensors | 传感器分压电路
A potential divider is the most common way to convert a sensor resistance change into a voltage. If a supply voltage V_s is connected across two resistors R₁ and R₂ in series, the output across R₂ is given by:
分压器是将传感器电阻变化转换为电压的最常用方法。如果电源电压 V_s 连接在串联的两个电阻 R₁ 和 R₂ 上，则 R₂ 两端的输出为：
V_out = V_s × R₂ / (R₁ + R₂)
If the sensor is placed as R₁ at the top of the divider and a fixed resistor is R₂ at the bottom, an increase in sensor resistance will decrease V_out. If the sensor is placed as R₂ at the bottom, an increase in sensor resistance will increase V_out.
如果传感器作为 R₁ 放在分压器上端，固定电阻作为 R₂ 放在下端，则传感器电阻增大将使 V_out 减小。如果传感器作为 R₂ 放在下端，则传感器电阻增大将使 V_out 增大。
For an NTC thermistor, resistance decreases as temperature rises. Placing the thermistor at the top and a fixed resistor at the bottom therefore gives a rising output voltage with temperature, which is useful for a temperature alarm.
对于 NTC 热敏电阻，温度升高时电阻减小。因此，将热敏电阻放在上端、固定电阻放在下端，可得到随温度升高而上升的输出电压，这可用于温度报警器。
For an LDR, resistance decreases as light intensity rises. Placing the LDR at the top gives a falling output voltage with increasing light, while placing it at the bottom gives a rising output voltage with increasing light.
对于光敏电阻，光强增大时电阻减小。将光敏电阻放在上端可得到随光强增大而下降的输出电压，而将其放在下端则得到随光强增大而上升的输出电压。
6. The Operational Amplifier Comparator | 运算放大器比较器
A comparator is an operational amplifier used without negative feedback. It compares the voltage at its inverting input V₁ with the voltage at its non-inverting input V₂.
比较器是一种无负反馈的运算放大器。它比较反相输入端电压 V₁ 与同相输入端电压 V₂。
If V₂ is greater than V₁, the output saturates at the positive supply voltage +V_s. If V₂ is less than V₁, the output saturates at the negative supply voltage −V_s or at 0 V for a single-supply comparator.
如果 V₂ 大于 V₁，输出饱和在正电源电压 +V_s。如果 V₂ 小于 V₁，输出饱和在负电源电压 −V_s，或在单电源比较器中为 0 V。
V_out ≈ +V_s if V₂ > V₁
V_out ≈ −V_s if V₂ < V₁
This sharp switching behaviour makes the comparator ideal for turning an output device on or off when a sensor signal crosses a set threshold. One input is usually a reference voltage from a variable resistor, and the other input is the sensor output.
这种陡峭的开关行为使比较器非常适合在传感器信号超过设定阈值时打开或关闭输出设备。一个输入端通常是由可变电阻提供的参考电压，另一个输入端是传感器输出。
In a temperature alarm, the reference voltage is set to the value corresponding to the desired alarm temperature. When the sensor voltage rises above the reference, the comparator output goes high and can switch on a buzzer or LED through a transistor.
在温度报警器中，参考电压被设置为与所需报警温度对应的值。当传感器电压超过参考值时，比较器输出为高电平，并可通过晶体管打开蜂鸣器或 LED。
7. Analogue-to-Digital Conversion | 模数转换
Many modern sensing systems use a microcontroller or digital display, so the analogue sensor signal must be converted into a digital number. This is done by an analogue-to-digital converter, or ADC.
许多现代传感系统使用微控制器或数字显示器，因此模拟传感器信号必须转换为数字量。这由模数转换器（ADC）完成。
The ADC samples the analogue voltage at regular intervals and assigns each sample to the nearest quantisation level. If the ADC has n bits, the number of possible digital levels is 2ⁿ.
ADC 以固定的时间间隔对模拟电压进行采样，并将每个样本分配到最接近的量化电平。如果 ADC 有 n 位，则可能的数字电平数为 2ⁿ。
A larger number of bits gives a higher resolution, meaning smaller changes in the analogue input can be detected. However, a higher resolution usually requires a longer conversion time or a more expensive ADC.
位数越多，分辨率越高，意味着可以检测到更小的模拟输入变化。然而，更高的分辨率通常需要更长的转换时间或更昂贵的 ADC。
The sampling rate must be at least twice the highest frequency present in the sensor signal to avoid aliasing. This is known as the Nyquist criterion.
采样频率必须至少是传感器信号中最高频率的两倍，以避免混叠。这称为奈奎斯特准则。
8. Processing and Control | 处理与控制
The processing block makes decisions based on the conditioned or digitised sensor signal. It may be a simple comparator circuit, a logic gate, or a programmable microcontroller.
处理模块根据经过调理或数字化的传感器信号作出决策。它可以是一个简单的比较器电路、一个逻辑门，或一个可编程微控制器。
In a basic system, the processing block might compare the sensor voltage with a preset reference and produce a high or low output. In a more advanced system, a microcontroller can store calibration data, apply corrections, and drive multiple outputs.
在基本系统中，处理模块可以将传感器电压与预设参考值进行比较，并产生高电平或低电平输出。在更高级的系统中，微控制器可以存储校准数据、进行修正并驱动多个输出。
Control logic can also introduce time delays or hysteresis, so that the output does not rapidly switch on and off when the sensor signal is near the threshold. Hysteresis prevents instability in control systems.
控制逻辑还可以引入时间延迟或迟滞，使传感器信号接近阈值时输出不会快速来回切换。迟滞可以防止控制系统不稳定。
If feedback is used, the processing block compares the current sensor value with a desired set point and adjusts an actuator until the difference, or error, is minimised.
如果使用反馈，处理模块会将当前传感器值与期望设定值进行比较，并调整执行器，直到差值（即误差）最小化。
9. Output Transducers and Actuators | 输出换能器与执行器
An output transducer converts an electrical signal back into a non-electrical form. Common output transducers include LEDs, buzzers, loudspeakers, filament lamps, and liquid crystal displays.
输出换能器将电信号转换回非电形式。常见的输出换能器包括 LED、蜂鸣器、扬声器、白炽灯和液晶显示器。
An actuator is an output device that produces movement or a physical action, such as a motor, relay, solenoid, or heater. Actuators allow the sensing system to control the environment rather than simply display a value.
执行器是产生运动或物理动作的输出设备，例如电动机、继电器、螺线管或加热器。执行器使传感系统能够控制环境，而不仅仅是显示数值。
The output device is often driven through a transistor because the processing circuit may not be able to supply enough current. A relay can be used to switch a high-power circuit from a low-power sensor signal.
输出设备通常通过晶体管驱动，因为处理电路可能无法提供足够的电流。继电器可用于通过低功率传感器信号切换高功率电路。
The choice of output transducer depends on the application: a buzzer is suitable for an alarm, an LED for a visual indicator, and a motor for a robotic or automatic control system.
输出换能器的选择取决于应用：蜂鸣器适用于报警器，LED 适用于视觉指示器，电动机适用于机器人或自动控制系统。
10. Sensitivity, Resolution and Range | 灵敏度、分辨率与量程
Sensitivity is defined as the change in output divided by the change in input. A sensor with high sensitivity produces a large output change for a small input change.
灵敏度定义为输出的变化量除以输入的变化量。高灵敏度的传感器在输入发生微小变化时会产生较大的输出变化。
Sensitivity = Δoutput / Δinput
Resolution is the smallest change in the physical quantity that the sensing system can detect. For a digital system, resolution is limited by the number of bits in the ADC and by the noise level of the analogue circuit.
分辨率是传感系统能够检测到的物理量的最小变化。对于数字系统，分辨率受 ADC 的位数以及模拟电路噪声水平的限制。
Range is the difference between the maximum and minimum values of the physical quantity that the sensor can measure accurately. A sensor with a wide range may have lower sensitivity, and a sensor with high sensitivity often has a narrow range.
量程是传感器能够准确测量的物理量的最大值与最小值之差。量程宽的传感器灵敏度可能较低，而灵敏度高的传感器量程通常较窄。
When comparing sensors, you should consider sensitivity, resolution, range, response time, and stability, because a single specification does not fully describe the performance of a sensing system.
在比较传感器时，应考虑灵敏度、分辨率、量程、响应时间和稳定性，因为单一指标不能完全描述传感系统的性能。
11. Response Time and Calibration | 响应时间与校准
Response time is the time taken for the sensor output to reach a specified percentage of its final value after a sudden change in input. A small response time means the system reacts quickly to changes.
响应时间是在输入突然变化后，传感器输出达到其最终值指定百分比所需的时间。响应时间短意味着系统能快速对变化作出反应。
Calibration is the process of measuring the sensor output at known input values and constructing a calibration curve or equation. It allows the system to convert an electrical signal into accurate physical units.
校准是在已知输入值下测量传感器输出，并构建校准曲线或方程的过程。它使系统能够将电信号转换为准确的物理单位。
Drift is a slow change in the sensor output over time when the input is constant. Drift can be caused by temperature changes, ageing, or moisture, and it reduces the accuracy of the sensing system.
漂移是输入不变时传感器输出随时间的缓慢变化。漂移可能由温度变化、老化或潮湿引起，它会降低传感系统的准确性。
A zero error occurs when the sensor gives a non-zero output for a zero input. This can be corrected by adding or subtracting a constant during calibration.
零点误差指传感器在输入为零时输出不为零。这可以通过在校准期间加上或减去一个常数来修正。
12. Design Example: Temperature Alarm | 设计实例：温度报警器
A simple temperature sensing system can be built using an NTC thermistor, a fixed resistor, a variable resistor, an operational amplifier comparator, a transistor, and a buzzer.
一个简单的温度传感系统可以使用 NTC 热敏电阻、固定电阻、可变电阻、运算放大器比较器、晶体管和蜂鸣器来构建。
The thermistor and fixed resistor form a potential divider. The variable resistor sets the reference voltage at the inverting input of the comparator, while the divider output is connected to the non-inverting input.
热敏电阻和固定电阻组成分压器。可变电阻在比较器的反相输入端设置参考电压，而分压器输出连接到同相输入端。
At low temperatures, the thermistor resistance is high, so the divider output is below the reference voltage and the comparator output is low. The transistor is off, and the buzzer is silent.
在低温下，热敏电阻阻值较大，分压器输出低于参考电压，比较器输出为低电平。晶体管截止，蜂鸣器不发声。
As the temperature rises, the thermistor resistance falls, causing the divider output to rise. When it exceeds the reference voltage, the comparator output goes high, the transistor turns on, and the buzzer sounds.
随着温度升高，热敏电阻阻值减小，分压器输出上升。当它超过参考电压时，比较器输出为高电平，晶体管导通，蜂鸣器发出声音。
This system is open-loop because the buzzer does not affect the temperature. A closed-loop version could use a heater and a relay, with feedback from the thermistor to maintain a constant temperature.
该系统是开环的，因为蜂鸣器不影响温度。闭环版本可以使用加热器和继电器，并利用热敏电阻的反馈来维持恒定温度。
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