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非性接触型仪器

在非接触型热电仪器中，加热元件和热电偶之间没有直接的电气连接。相反，这两个组件被一层电绝缘材料隔开。虽然这种绝缘提供了电气隔离，但它也对仪器的性能产生了显著影响。与接触型仪器相比，非接触设计使系统对被测量量的变化不太敏感，并且响应时间更慢。这是因为加热元件与热电偶之间的热传递由于绝缘屏障的存在而效率较低。

Vacuum Thermo - Element

In vacuum tube - based thermoelectric instruments, both the heater and the thermocouple are enclosed within an evacuated glass tube. This vacuum environment significantly enhances the efficiency of the instrument. By eliminating the presence of air, heat loss through convection and conduction is minimized. As a result, the heater can retain its heat for an extended period, ensuring a more stable and consistent heat source for the thermocouple. This stability in heat generation leads to more accurate and reliable measurements over time.

Bridge Type

In bridge - type thermoelectric instruments, the electric current flows directly through the thermocouple. As the current passes, it causes the temperature of the thermocouple to rise. The magnitude of this temperature increase is directly proportional to the root - mean - square (RMS) value of the current. This direct relationship between the current, temperature change, and resulting electrical output from the thermocouple forms the basis of how these instruments accurately measure electrical quantities, providing a reliable and efficient method for various measurement applications.

Advantages of Thermoelectric Instruments

Thermoelectric instruments offer several notable benefits, making them valuable tools in electrical measurement and analysis:

• Direct RMS Indication: One of the key advantages is the ability to directly display the root - mean - square (RMS) values of voltage and current on the waveform. This feature simplifies the measurement process, allowing users to quickly and accurately determine these crucial electrical parameters without the need for additional calculations or complex conversion methods.

• Immunity to Stray Magnetic Fields: These instruments are inherently resistant to the influence of stray magnetic fields. This immunity ensures more accurate and reliable measurements, as external magnetic disturbances do not interfere with the instrument's operation or skew the results. In environments where magnetic interference is common, such as near electrical machinery or power lines, this advantage becomes particularly significant.

• Broad Current Measurement Range: The thermoelectric elements employed in these instruments enable a wide range of current measurements. Whether dealing with low - current or high - current applications, thermoelectric instruments can accurately capture and display the relevant values, making them versatile for various electrical systems and experimental setups.

• High Sensitivity: Thermoelectric instruments exhibit a high degree of sensitivity, allowing them to detect even small changes in electrical quantities. This sensitivity is crucial for precise measurements in applications where minute variations in voltage or current can have significant implications, such as in research laboratories or in the calibration of other electrical devices.

• Potentiometer Calibration Utility: They are extremely useful for calibrating potentiometers. By leveraging the accuracy of a standard cell, thermoelectric instruments can help ensure the proper functioning and accuracy of potentiometers, which are essential components in many electrical circuits for voltage regulation and measurement.

• Frequency - Independent Operation: Thermoelectric elements are free from frequency errors, enabling these instruments to be used across an extensive range of frequencies. This characteristic makes them suitable for applications involving alternating current (AC) signals of varying frequencies, from low - frequency power systems to high - frequency electronic circuits.

Disadvantages of Thermoelectric Instruments

Despite their many strengths, thermoelectric instruments do have one notable limitation:

• Limited Overload Capacity: Compared to other types of electrical measurement elements, thermoelectric instruments have a relatively low overload capacity. This means that they are more vulnerable to damage or inaccurate readings when exposed to electrical currents or voltages that exceed their rated limits. As a result, careful consideration and proper protection measures must be taken when using these instruments in applications where overload conditions may occur to avoid potential instrument failure or compromised measurement accuracy.