【2025 Knowledge Accumulation】Questions 1–3 with answers
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This post was last edited by The one on 2025-11-27 11:21. 1. Among the following four situations, which one is most likely to cause abnormalities in the 4-20mA signal transmission? A. The air-conditioning temperature in the control room is set at 24°C. B. Signal cables and power cables are laid parallel to each other in the same tray. C. The supply voltage for the transmitters is 24.5V DC. D. Shielded cables are used to transmit signals. Answer: B. Reason: Power cables generate strong electromagnetic interference; if laid parallel to signal cables, they can severely disrupt the 4-20mA signals, resulting in fluctuations or distortions in the measurement values. Other options: A Normal ambient temperature ； The C supply voltage is within the allowable range ； It is correct to use shielded cables for D.
2. The nominal resistance value of a Pt100 thermistor at 0°C is 100Ω. What is its approximate temperature when the measured resistance is 115Ω? A. 0℃ B. 39℃ C. 115℃ D. 150℃ Answer: B Reasoning: Based on the resistance-temperature relationship of Pt100, the rate of change in resistance is approximately 0.385Ω/℃. The change in resistance is 115Ω – 100Ω = 15Ω. Therefore, the temperature ≈ 15Ω / 0.385 Ω/℃ ≈ 39℃.
3. When measuring the liquid level in a sealed container, the differential pressure transmitter is installed 0.5 m below the lowest liquid level. The density of the medium is 1000 kg/m³. What is required is: A. No migration B. Positive migration with a migration amount of 4.9 kPa C. Negative migration with a migration amount of 4.9 kPa D. Positive migration with a migration amount of 0.5 kPa. Answer: B. Reasoning: Installing the transmitter below the lowest liquid level creates a fixed static pressure: ρgh = 1000 × 9.8 × 0.5 = 4900 Pa = 4.9 kPa. To output 4mA when the liquid level is 0, positive migration is required, with a migration amount of 4.9 kPa.
Below are the links to Siemens selection software for reference. (1) TIA_Selection_Tool_cloud (online cloud version) https://mall.industry.siemens.com/tst/#/Start
(2) TIA_Selection_Tool (offline standalone version) link: https://pan.baidu.com/s/1RnNeuZwyPdHaYUBT8aGrVA Extraction code: 1111
(3) TIA_Selection_Tool tutorial link: https://pan.baidu.com/s/1SJMVlsJUqrNDWdtkssMHHQ Extraction code: 1111
(4) SIZER_V3.23 link: https://pan.baidu.com/s/1AC8dygWdfic8gqyACwbNPg Extraction code: 1111
(5) SIZER_V3.22 link: https://pan.baidu.com/s/1iFh9tnFqNskmLayP2P87qw Extraction code: 1111
(6) SIZER_V3.21 link: https://pan.baidu.com/s/1qlA2R4FMKoZGzHzOxpihPQ Extraction code: 1111
(7) SIZER_V3.20 link: https://pan.baidu.com/s/1rn8W4Zkr2G3t_Io9u3nKXA Extraction code: 1111
(8) SIZER_V3.19 link: https://pan.baidu.com/s/1bOkJLZR5kx_nsgfJ5Ht2Mg Extraction code: 1111