Common Terminology in Process Instruments

In modern industrial production processes, process instruments play a critical role. Through precise measurement and control, they ensure the stability and efficiency of production processes. Whether it's temperature, pressure, flow, or liquid level, process instruments provide real-time data monitoring and feedback, offering a scientific basis for optimizing production processes. As AUTO Instrument, we understand the importance of accurate and reliable process control in enhancing industrial automation. Therefore, in this article, we will introduce some common professional terms used in process instruments to help you better understand the working principles and applications of these complex devices, ensuring that you can operate them skillfully and improve production efficiency and safety.

The types of pressure transmitters typically include the following categories: differential pressure transmitters, absolute pressure transmitters, flange liquid level transmitters, radar level meters, ultrasonic flow meters, vortex flow meters, turbine flow meters, electromagnetic flow meters, etc.

1. Range The algebraic difference between the upper and lower limit values of a given range. Example: A temperature sensor with a measurement range of 50°C to 150°C has a range of 100°C.

2. Output Signal The form in which the instrument converts measured values into usable signals, such as current (e.g., 4-20mA), voltage (e.g., 0-10V), or digital signals (e.g., Modbus). Example: A pressure transmitter’s output is 4-20mA to reflect the measured pressure.

3. Response Time The time required for the instrument to reach a new steady output after receiving a signal change. Example: A temperature sensor takes 1 second to update its output after detecting a temperature change.

4. Step Response Time The time needed for the instrument to reach a stable output when the input signal suddenly changes from one value to another. Example: When the pressure suddenly increases from 10 bar to 20 bar, the transmitter needs 0.5 seconds to stabilize the output.

5. Time Constant The system's speed of response to input changes, typically referring to the time it takes to reach 63.2% of the final value. The smaller the time constant, the faster the system responds. Example: A temperature sensor with a time constant of 2 seconds means that it will reach 63.2°C when the temperature rises from 0°C to 100°C in 2 seconds.

6. Reverse Polarity Protection A function that prevents damage to the instrument when the power supply connections are reversed. Example: If the transmitter's positive and negative terminals are connected incorrectly, it will not be damaged.

7. Turndown Ratio The ratio of the maximum measurement range to the minimum measurement range. Example: A sensor with a measurement range of 0-100 bar has a turndown ratio of 10:1, allowing it to be used in a 0-10 bar range.

8. Long-term Stability The ability of the instrument to maintain accuracy over extended use. Example: A pressure transmitter maintains an output error of ±0.1% after 5 years of use.

9. Process Temperature The temperature range of the medium (liquid or gas) directly in contact with the instrument. Example: A flowmeter measuring hot water may have a process temperature of up to 90°C.

10. Ambient Conditions The surrounding environment of the instrument, including factors such as temperature, humidity, and vibration. Example: The ambient conditions require a temperature range of -20°C to 50°C and humidity of 80%.

11. Storage Temperature The temperature range in which the instrument can be safely stored when not in use. Example: The device can be stored in a cold warehouse with a minimum temperature of -40°C.

12. Climatic Class The ability of the device to function under specific climatic conditions, usually defined by standards. Example: An instrument marked with an "industrial-grade" climatic class is suitable for use in humid environments.

13. IP Rating (Ingress Protection Rating) The degree to which the instrument's casing protects against dust and water. Represented by "IPxx," where "xx" is a number. Example: An IP68 sensor is completely dustproof and can be submerged in water for extended periods.

14. EMC (Electromagnetic Compatibility) The instrument’s ability to function without interference in an electromagnetic environment and not produce interference itself. Example: A transmitter installed in a factory will not have its signal disrupted by motor noise.

15. Process Connection The type of interface between the instrument and the process equipment, such as threads or flanges. Example: A level meter is connected to a tank via a flange.

16. Electrical Connection Refers to how the instrument is wired to the power supply or control system, such as using a junction box or connector. Example: A common M12 electrical connector.

17. Ripple Small fluctuations or noise in the output signal. Example: A 4-20mA signal has a fluctuation of ±0.1mA.

18. Noise Unwanted interference or fluctuations in a signal. Example: Electromagnetic interference can cause fluctuations in the sensor output.

19. NAMUR An international standard organization that defines the interface and usage specifications for process instruments. Example: A NAMUR-compliant sensor can be directly connected to a PLC.

20. Low Flow Cut-off A function used to filter out meaningless signals below a certain threshold. Example: A flowmeter ignores flow signals below 1 L/h.

21. Start-up Time The time required for the instrument to reach normal operating condition after being powered on. Example: A sensor requires 3 seconds to start outputting data after being powered on.

22. Excitation Frequency The frequency of the electrical signal that drives the sensor. Example: The excitation frequency for an electromagnetic flowmeter is 50 Hz.

23. Mechanical Load The maximum external force that the device can withstand, such as pressure or vibration. Example: An instrument mounted on a vibrating platform can withstand a force of 20N.

24. Power Consumption The amount of power the instrument consumes during operation. Example: A pressure transmitter consumes 1.5W.

25. Explosion-proof Certification Certification indicating that the instrument is safe to use in explosive gas environments. Example: A transmitter with ATEX certification can be used on an oil platform.

26. Pollution Degree Indicates the suitability of the device for use in environments with varying degrees of contamination. Example: A device with pollution degree 3 is suitable for industrial environments.

27. Repeatability The consistency of the instrument's measurements under the same conditions. Example: A temperature sensor consistently outputs 99°C with each measurement.

28. Non-repeatability Refers to the inconsistency error in measurements taken multiple times. Example: Measuring the same temperature results in fluctuations of ±0.5°C.

29. Write Protection A feature that prevents settings from being accidentally changed. Example: Once write protection is enabled on a pressure transmitter, its set values cannot be modified.

30. Signal-to-Noise Ratio The ratio of signal strength to noise strength, used to assess signal quality. Example: A high signal-to-noise ratio means more accurate measurements.

31. Signal Dynamic Range The ratio of the smallest to the largest signal that the device can effectively handle. Example: A sensor with a wide dynamic range can detect both weak and strong signals.

32. Load Stability The ability of the instrument to maintain stable output under varying load conditions. Example: A pressure transmitter maintains consistent output even as the load changes.

33. Unipolar and Bipolar

· Unipolar: The signal has only positive or negative values. Example: A 0-10V voltage signal.

· Bipolar: The signal has both positive and negative values. Example: A -10V to 10V signal.