I. Advantages and disadvantages of linear displacement sensors
The advantages of linear displacement sensors are:
(1) It can realize any functional relationship between the output and the input;
(2) It has a simple structure, small size, light weight, low price, and stable performance;
(3) The output signal is large, and generally no amplification is required;
(4) It is less affected by environmental factors (such as temperature, humidity, electromagnetic interference, etc.).
Disadvantages: Because of the friction between the brush and the resistive film, a large input energy is required. Wear will affect the service life and reduce reliability, thus reducing measurement accuracy.
II. Determining the Quality of a Linear Displacement Sensor
A linear displacement sensor is a linear device with electrical properties, which converts various physical quantities into electrical quantities when in operation. Therefore, several aspects are crucial when using a linear displacement sensor; otherwise, damage can easily occur. So how do we determine if a linear displacement sensor is damaged? Here's what I've shared:
1. Use a digital multimeter to test the resistance.
If the resistance of a linear displacement sensor is 5KΩ, then when using a digital multimeter to check the resistance at the positive and negative terminals of the power supply, the resistance should be 5KΩ + 5% and the signal should be stable without fluctuations; otherwise, it is considered damaged. To check the resistance at the power supply and output terminals with a digital multimeter, pull out the linear displacement sensor lever. If the resistance changes uniformly from 0 to 5KΩ, the linear displacement sensor is functioning correctly.
2. Zero-point detection
A typical linear displacement sensor with current or voltage output operates at 24VDC. Power it with a linear power supply and use a digital multimeter to test the output. If the zero-point output (without pulling the lever) is within 4mA+5% or 0V+5%, it is considered normal. When the lever is fully extended, an output of 20mA+5% or 10V+5% is considered normal. Otherwise, it is considered damaged. If the data fluctuates irregularly, it is likely due to incorrect wiring causing a short circuit and damaging the linear displacement sensor.
This concludes our sharing on how to determine if a linear displacement sensor is damaged. The signals from a linear displacement sensor, whether voltage or current, are analog signals. Once a zero point and reference are set, analog signals are generally absolute signals. These signals will not be lost during transmission, nor will they err.
III. Common Faults and Troubleshooting of Linear Displacement Sensors
1. If the linear displacement sensor's ruler has been used for a long time, and the seal has aged, containing many impurities, and the mixture of water and oil severely affects the contact resistance of the brushes, causing the displayed numbers to fluctuate continuously, then the linear displacement sensor's ruler is likely damaged and needs to be replaced.
2. If the power supply capacity is too small, many problems will arise. Therefore, the power supply needs to have sufficient capacity. Insufficient capacity will cause the following issues: the movement of the molten plastic will cause fluctuations in the display of the mold closing electronic ruler, or the movement of the mold closing will cause fluctuations in the display of the injection electronic ruler, resulting in large measurement errors. These problems are more likely to occur if the solenoid valve's drive power supply and the linear displacement sensor's power supply are connected simultaneously. In severe cases, voltage fluctuations can even be measured with a multimeter in voltage mode. If the problem is not caused by high-frequency interference, electrostatic interference, or insufficient neutralization, then it is likely due to insufficient power supply capacity.
3. Both frequency modulation interference and electrostatic interference can cause the display numbers on the linear displacement sensor's electronic ruler to fluctuate. The signal line of the electronic ruler must be kept in a separate cable tray from the equipment's power lines. The electronic ruler must be forcibly grounded, and the casing of the electronic ruler must be in good contact with the ground. The signal line needs to be shielded, and one end of the electrical box should be grounded to the shield. With high-frequency interference, a multimeter voltage measurement will usually show normal readings, but the displayed numbers will fluctuate continuously; the same situation occurs with electrostatic interference. To verify if it is electrostatic interference, you can short-circuit the electronic ruler's cover screws with some metal parts on the machine using a power cord. Short-circuiting will immediately eliminate the electrostatic interference. However, eliminating high-frequency interference is difficult using the above method. Frequency converters and robotic arms frequently experience high-frequency interference, so you can try stopping the high-frequency converter or robotic arm to verify if it is high-frequency interference.
4. If the linear displacement sensor's electronic ruler displays data that jumps regularly at a certain point during operation, or if no data is displayed, it is necessary to check whether the insulation of the connecting wire is damaged and whether it is making regular contact with the machine's casing, resulting in a short circuit to ground.
5. The power supply voltage must be stable. Industrial voltages need to meet a stability requirement of ±0.1%. For example, if the reference voltage is 10V, a fluctuation of ±0.01V is permissible. Otherwise, it will cause fluctuations in the display. However, if the amplitude of the display fluctuation does not exceed the amplitude of the voltage fluctuation, then the electronic ruler is normal.
6. During the connection process, extra care must be taken. The three wires of the electronic ruler must not be connected incorrectly, and the power wire and output wire cannot be interchanged. If the above wires are connected incorrectly, a large linear error will occur, which will be difficult to control, the control accuracy will become very poor, and the display will easily exhibit fluctuations, etc.
