Interpretation of Linear Variable Differential Transformer (LVDT) voltage output

In summary, the conversation discusses the use of a Linear Variable Differential Transformer (LVDT) for measuring distance and the issue of discrepancies between the calibrated sensitivity values and the actual voltage output of the LVDT. The speaker is unsure whether to use the fitted curve from their measurements or get the LVDT re-calibrated. The responder suggests using the measured values if they meet the needed accuracy.
  • #1
ca2n
10
0
Good day to all Physics Forums members,

I am currently undertaking a project which involves the use of a Linear Variable Differential Transformer (LVDT) to measure the distance an object makes between two points. My setup is as follows:

  1. LVDT Type: Solartron DC50 with sensitivity of 6.158 mV/V/mm at 10 VDC
  2. Power supply to LVDT: 12.12 VDC (const. and cannot be varied)
  3. Voltage output from LVDT fed to dataTaker data acquisition system

In an attempt at verifying the calibrated sensitivity of the LVDT, I performed a number of height measurements using gauge blocks. I took 6 equally-spaced height intervals between the maximums of the LVDT range and plotted the LVDT voltage output vs. height. Here is what I encountered:

  1. The curve plotted was NOT linear as I anticipated it to be. As a matter of fact, the curve fit a polynomial equation of degree five with R2 = 1
  2. When comparing the LVDT output voltage with the LVDT calibrated sensitivity values, discrepancies occured, e.g. a 20 mm difference between two gauge block heights returned a 20.5 mm difference calculated from the voltage output of the LVDT. The discrepancies grew as the ends of the LVDT were approached.

My questions are:

  1. Could the fitted curve be beneficial for my use seeing as I've determined the end-to-end output values of the LVDT, OR,
  2. Should I, instead, just get the LVDT calibrated and use the obtained sensitivity value.

To be frank, I would highly prefer Option 1, if it is in fact a justifiable solution.

Any help is much appreciated. Thanks. :smile:
 
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  • #2
From your quoted numbers, the accuracy is 2.5% of reading. Considering that your supply voltage is over 20% high, that isn't bad at all. If 2.5% is within your needed accuracy, use it as is.

I see no reason to "...get the LVDT calibrated...", you just did when you measured the gauge blocks. Use those numbers if you need the accuracy.

Cheers,
Tom
 

FAQ: Interpretation of Linear Variable Differential Transformer (LVDT) voltage output

1. How does a Linear Variable Differential Transformer (LVDT) measure displacement?

An LVDT measures displacement by converting it into an electrical signal. The LVDT consists of a primary coil, two secondary coils, and a ferromagnetic core. When the core moves, it induces a voltage in the secondary coils, which can be measured as the output voltage. The magnitude and direction of the displacement can be determined by the difference in voltage between the two secondary coils.

2. What is the working principle of an LVDT?

The working principle of an LVDT is based on inductance. The core of the LVDT is placed inside the primary coil, which is connected to an AC power source. The two secondary coils are connected in series but in opposite directions, so their output voltages cancel out when the core is in the center position. As the core moves, the inductance of the secondary coils changes, resulting in a difference in voltage between the two coils.

3. What are the advantages of using an LVDT for displacement measurement?

LVDTs offer several advantages for displacement measurement, including high accuracy, linearity, and resolution. They also have a wide measurement range and can operate in harsh environments with high temperatures, vibrations, and electromagnetic interference. Additionally, they have a long lifespan and require little to no maintenance.

4. How is an LVDT calibrated?

An LVDT can be calibrated by applying known displacements and recording the corresponding output voltages. A calibration curve can then be created to convert output voltage to displacement. This can be done using a calibration standard or by comparing the LVDT output to that of a reference sensor. Regular calibration is important to ensure accurate and reliable measurements.

5. What are some common applications of LVDTs?

LVDTs are commonly used in industrial, automotive, and aerospace applications for measuring linear displacements. They are also used in geotechnical engineering for monitoring the movement of structures and in medical devices for measuring bodily movements. Additionally, LVDTs are used in quality control and testing to ensure the accuracy and precision of manufactured products.

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