Measuring Primary Coil Resistance of Turbine LVDT Displacement Sensor TDZ-1E-41

In the steam turbine control system, the LVDT displacement sensor is one of the core components, and its performance directly affects the accuracy and stability of the equipment. As a common model in thermal power plant applications, the TDZ-1E-41 displacement sensor relies on the measurement of coil resistance to determine its working state. Measuring the resistance of the primary coil with a multimeter can not only preliminarily determine whether the sensor is damaged, but also provide an important basis for subsequent troubleshooting. Below we will systematically explain how to complete this detection task scientifically and safely from the aspects of technical principles, operating procedures and precautions.

I. Measurement purpose and technical principles

The core structure of the LVDT position sensor TDZ-1E-41 consists of a primary coil and a secondary coil. When the iron core moves with the measured object, the output voltage of the secondary coil will differ due to the change in magnetic flux, thereby reflecting the displacement. The resistance value of the primary coil is closely related to its coil winding process, material properties and internal connection status. Under normal circumstances, the resistance value of the primary coil should be within the range specified by the manufacturer. If the resistance value rises or falls abnormally, it may indicate problems such as short circuit, open circuit or poor contact between coil turns. Therefore, measuring the resistance of the primary coil is an important means to determine whether the sensor is intact.

II. Preparation before measurement

• Power off and safety measures

Before starting the measurement, make sure that the sensor is completely powered off. The LVDT sensor TDZ-1E-41 is usually connected to the turbine control system or servo loop. Live operation may cause equipment damage or personal injury. After disconnecting the power supply, it is recommended to wait for a few minutes to release any residual charge and use a voltage tester to confirm that there is no residual voltage. In addition, insulating gloves and goggles should be worn to avoid injury caused by accidental electric shock or splashing.

• Tool and equipment inspection

Select a high-precision digital multimeter and ensure that its battery is fully charged. The probes of the multimeter must be clean and unworn to avoid contact resistance interfering with the measurement results. At the same time, prepare the specification sheet or technical parameter table of the sensor to compare the difference between the measured value and the nominal value.

• Environmental condition control

The measurement environment should avoid high temperature, high humidity or strong electromagnetic interference. If operating in a humid environment, a moisture-proof tool kit or temporary sealing of the sensor is required to prevent moisture from affecting the measurement accuracy. In addition, ensure that the installation position of the displacement sensor TDZ-1E-41 is stable to avoid vibration that causes the coil or lead to loosen.

III. Measurement steps and key details

The wiring terminals of the TDZ-1E-41 LVDT sensor are usually divided into three groups: primary coil terminals (P1, P2), secondary coil terminals (S1, S2) and common terminals (GND). When measuring the resistance of the primary coil, it is necessary to confirm that P1 and P2 are the correct terminals to avoid accidentally touching the secondary coil or common terminal. If the sensor housing is not clearly marked, the terminal definition can be checked through technical drawings or historical records.

Set the multimeter to resistance measurement mode and select the appropriate range. Connect the red and black probes to the P1 and P2 terminals respectively, and pay attention to keep the probes in full contact with the terminal surface. If the sensor lead is long or there is a connector, it is necessary to measure the resistance between the internal solder joint of the connector and the terminal to eliminate the influence of the connection fault.

When measuring, it is necessary to read the resistance value multiple times and take the average value to reduce accidental errors. For example, if one measurement shows 120Ω and another shows 122Ω, it can be determined to be 121Ω. Then, compare the measured value with the nominal value in the technical parameter table. If the deviation is within the allowable range, the primary coil state can be considered normal; if it deviates significantly from the nominal value, it is necessary to further check whether the coil is short-circuited, open-circuited, or partially damaged.

Based on the static measurement, a slight manual adjustment test can be performed: by rotating the sensor housing or fine-tuning the core position, observe whether the resistance value fluctuates. If the resistance value fluctuates significantly with the action, it may indicate that the insulation between the coil turns is damaged or the core offset causes a local short circuit. In addition, the overall function of the sensor can be further verified by combining the secondary coil voltage measurement (which needs to be performed in the power-on state).

IV. Common problems and countermeasures

1.Possible reasons for abnormal measurement values ​​are:

• Poor contact: Terminal oxidation, cold soldering, or unclean probe contact surface may cause falsely high resistance values. At this time, the terminal surface needs to be cleaned or the connection point needs to be re-welded.

• Coil inter-turn short circuit: If the resistance value is significantly lower than the nominal value, the inter-turn short circuit may be caused by the damage of the insulation layer of the coil winding. This type of fault requires the sensor to be replaced or returned to the factory for repair.

• Open circuit fault: When the resistance value is infinite or close to infinity, it indicates that the coil is open circuited. In this case, the sensor can no longer work properly and needs to be immediately stopped and replaced.

• Environmental interference: In a high humidity environment, the insulation performance of the coil may decrease due to moisture absorption, and the resistance value fluctuates. The sensor needs to be dried or the installation environment needs to be improved.

2. Avoidance of misjudgment risk:

• Temperature influence: The resistance value of the copper coil is positively correlated with temperature changes (temperature increases, resistance increases). If the ambient temperature deviates from the standard value during measurement, the measured value needs to be corrected according to the temperature coefficient.

• Multi-sensor interference: If multiple sensors share the same control cabinet, it is necessary to confirm that the multimeter probe does not accidentally touch other sensor coils to avoid mismeasurement.

• Probe polarity error: Some multimeters need to distinguish polarity when measuring low resistance values. If the probe polarity is reversed, the measured value may be distorted due to the diode effect.

V. Subsequent processing and maintenance recommendations

After completing the measurement, take appropriate measures based on the results. If the displacement sensor TDZ-1E-41 is in normal condition, the power supply can be restored and its operation can continue to be monitored; if a fault is found, it is necessary to decide whether to replace it immediately based on the on-site working conditions. For steam turbine control systems, it is recommended to replace the sensor during shutdown and maintenance to avoid the risk of operation during operation. If online replacement is required, safety regulations should be strictly followed, such as closing the relevant oil circuit stop valve, locking the control loop, etc., and professional personnel should monitor the entire process.

In addition, regular maintenance is the key to preventing failures. It is recommended to measure the sensor coil resistance once a quarter and record the data trend. If the resistance value is found to gradually deviate from the nominal value, even if the fault threshold has not been reached, maintenance should be arranged in advance.

When looking for high-quality, reliable LVDT displacement sensors, YOYIK is undoubtedly a choice worth considering. The company specializes in providing a variety of power equipment including steam turbine accessories, and has won wide acclaim for its high-quality products and services. For more information or inquiries, please contact the customer service below:
E-mail: sales@yoyik.com
Tel: +86-838-2226655
Whatsapp: +86-13618105229

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