Introduction: Usually, we only focus on whether the range of a sensor meets the testing requirements. In fact, there are many other aspects to consider when selecting a sensor. This article will take the most commonly used current sensor as an example and teach you how to select the right sensor step by step.
In testing, engineers frequently use sensors. Therefore, choosing the right sensor is paramount. Often, we only focus on whether the sensor's range meets the testing requirements. However, there are many other factors to consider when selecting a sensor. This article will use the most commonly used current sensor as an example to guide you step-by-step in choosing the appropriate sensor.
1. Measuring range
Measuring range is the most important indicator, and also the area most prone to problems. Generally, when selecting a sensor, we focus on its compatibility with the instrument's range. Taking the LEMITN1000-S sensor paired with a PA5000H 50A power board as an example, the PA5000H's minimum range is 1A, and the smallest value the instrument can display is 1.5% of the current range. This means the instrument cannot display values below 15mA. The LEMITN1000-S sensor has a transformation ratio of 1:1500. When the measured current is 22.5A, the sensor's corresponding output is exactly 15mA. Therefore, the LEMITN1000-S sensor paired with the PA5000H 50A power board cannot measure currents below 22.5A.
Using the PA5000H with a 5A board at this time is more suitable, because the minimum range of the 5A board is 10mA, and the output current value of the sensor above 0.15mA can be displayed (at this time, the instrument and sensor can measure a minimum of 225mA).
Figure 1 ITN1000-S sensor
If users need to use both a 50A board and an ITN sensor simultaneously, it is recommended to equip the PATV-33 adapter. It is actually a high-precision resistor that can convert the sensor's current signal into a voltage signal and input it to the BNC port of the power analyzer for testing. This can solve the problem that large-range power boards cannot test small currents.
2. Bandwidth
Similar to instruments, sensors also have bandwidth parameters, especially in industries that measure high-frequency signals, such as motors. Efficiency often exceeds 1 or is too low, and in many cases, this is due to insufficient sensor bandwidth. According to the barrel effect, the bandwidth of the entire test system is determined by the lowest bandwidth component. For example, a PA5000H with a 5M bandwidth paired with a 100K bandwidth sensor will result in a system bandwidth of only 100K. This may not make a significant difference when testing low-frequency signals, but it could lead to inaccurate measurements when testing high-frequency signals due to insufficient bandwidth.
3. Sensor type
For example, current sensors generally include voltage-type current sensors and current-type current sensors. These operate on different principles, resulting in different output signal types. Most Hall effect sensors are closed-type sensors, offering high measurement accuracy and outputting a current signal; examples include the LEMIT and LF series. In this case, simply setting the corresponding ratio in the instrument is sufficient. Voltage-type current sensors typically use a BNC connector, such as current clamps and oscilloscope current probes. They convert current signals into voltage signals, requiring the corresponding external sensor and transformation ratio to be set within the instrument. Furthermore, for special sensors with integrators, such as Rogowski coils, not all instruments currently support them; confirmation with the instrument manufacturer is necessary.
Figure 2. Schematic diagram of current sensor input.
Figure 3. Schematic diagram of voltage-type current sensor input.
4. Precision and Aperture
Accuracy is a very important indicator when selecting a sensor. The choice can be made according to the needs. Different levels of accuracy will have different prices. At the same time, it should be noted that if the test wire is thick, the aperture size needs to be considered. Generally, the sensor specification table will have the corresponding instructions. It is recommended to choose an aperture size that is as close as possible to the thickness of the wire to ensure high-precision testing.
5. AC/DC testing
When selecting a sensor, it is important to consider whether the sensor's test signal is AC, DC, or a combination of both. For example, many clamp sensors can only test AC signals, as can Rogowski coils.
6. Temperature and Delay
When testing in high-temperature environments, it is important to pay attention to the sensor's test temperature range. Generally, the sensor's nominal accuracy is within 25 degrees Celsius at room temperature. Temperature fluctuations can affect the sensor's accuracy. For different sensor models, it is necessary to consult the manufacturer for specific details.
In addition, when performing high-frequency signal testing, the delay has a significant impact on accuracy. Different types of sensors have different delays. The delay of a Hall sensor is much greater than that of a Rogowski coil. If there is a need for high-frequency testing, the delay of the Hall sensor can be calibrated separately. The PAH series power analyzer supports inputting the delay into the instrument for internal calibration, effectively ensuring the accuracy of high-frequency signal testing.
With the booming development of the new energy industry, the use of sensors in power analyzers is becoming increasingly common. Even the smallest error can lead to significant discrepancies. The choice of sensor has a crucial impact on overall test accuracy. Mastering the key points in this article will greatly improve the accuracy of your daily tests. ZLG Zhiyuan Electronics, leveraging its years of experience in test and measurement, will provide reliable testing solutions to the industry, contributing to its development!
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